Audio/Video Transport WG S. Wenger Internet Draft Y.-K. Wang Intended status: Standards track Nokia Expires: November 2008 T. Schierl Fraunhofer HHI A. Eleftheriadis Vidyo May 15, 2008 RTP Payload Format for SVC Video draft-ietf-avt-rtp-svc-09.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on November 15, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Wenger, et al Expires November 15, 2008 [Page 1] Internet-Draft RTP Payload Format for SVC Video May 2008 Abstract This memo describes an RTP payload format for scalable video coding (SVC) defined in_Annex G of the ITU-T Recommendation H.264 video codec which is technically identical to Amendment 3 of ISO/IEC International Standard 14496-10. The RTP payload format allows for packetization of one or more Network Abstraction Layer (NAL) units, produced by the video encoder, in each RTP packet payload. The payload format has wide applicability, such as low bit-rate conversational, Internet video streaming, or high bit-rate entertainment quality video. Table of Contents 1. Introduction...................................................3 2. Conventions....................................................4 3. The SVC Codec..................................................4 3.1. Overview..................................................4 3.2. Parameter Set Concept.....................................6 3.3. Network Abstraction Layer Unit Header.....................7 4. Scope.........................................................10 5. Definitions and Abbreviations.................................12 5.1. Definitions..............................................12 5.1.1. Definitions Per SVC Specification...................12 5.1.2. Definitions Local to This Memo......................14 5.2. Abbreviations............................................16 6. RTP Payload Format............................................17 6.1. Design Principles........................................17 6.2. RTP Header Usage.........................................17 6.3. Common Structure of the RTP Payload Format...............17 6.4. NAL Unit Header Usage....................................17 6.5. Packetization Modes......................................19 6.5.1. Packetization Modes for Session Multiplexing........19 6.6. Decoding Order Number (DON)..............................22 6.6.1. Cross-Session DON (CS-DON) for Session Multiplexing.22 6.7. Aggregation Packets......................................24 6.8. Fragmentation Units (FUs)................................24 6.9. Payload Content Scalability Information (PACSI) NAL Unit.24 7. Packetization Rules...........................................31 7.1. Packetization Rules for Session Multiplexing.............32 8. De-Packetization Process......................................34 8.1. De-Packetization Process for Session Multiplexing........35 8.1.1. Decoding Order Recovery for the NI-T and NI-TC Modes35 Wenger, et al Expires November 15, 2008 [Page 2] Internet-Draft RTP Payload Format for SVC Video May 2008 8.1.2. Decoding Order Recovery for the NI-C, NI-TC and I-C Modes......................................................38 9. Payload Format Parameters.....................................39 9.1. Media Type Registration..................................40 9.2. SDP Parameters...........................................50 9.2.1. Mapping of Payload Type Parameters to SDP...........51 9.2.2. Usage with the SDP Offer/Answer Model...............51 9.2.3. Usage with Session Multiplexing.....................56 9.2.4. Usage in Declarative Session Descriptions...........56 9.3. Examples.................................................57 9.3.1. Example for Offering A Single SVC Session...........57 9.3.2. Example for Offering Session Multiplexing...........58 9.4. Parameter Set Considerations.............................59 10. Security Considerations......................................59 11. Congestion Control...........................................59 12. IANA Consideration...........................................60 13. Informative Appendix: Application Examples...................60 13.1. Introduction............................................60 13.2. Layered Multicast.......................................61 13.3. Streaming of An SVC Scalable Stream.....................61 13.4. Multicast to MANE, SVC Scalable Stream to Endpoint......62 13.5. Scenarios Currently Not Considered......................64 13.6. SSRC Multiplexing.......................................65 14. References...................................................66 14.1. Normative References....................................66 14.2. Informative References..................................67 15. Authors' Addresses...........................................68 Intellectual Property Statement..................................69 Disclaimer of Validity...........................................69 Acknowledgement..................................................69 16. Open Issues..................................................70 17. Changes Log..................................................70 From draft-ietf-avt-rtp-svc-08 to draft-ietf-avt-rtp-svc-09......70 1. Introduction This memo specifies an RTP [RFC3550] payload format for the Scalable Video Coding (SVC) extension of the H.264/AVC video coding standard. Formally, SVC takes the form of Amendment 3 to ISO/IEC 14496 Part 10 [MPEG4-10], and Annex G of ITU-T Rec. H.264/AVC [H.264]. The specification of SVC is available in [SVC]. SVC covers the whole application ranges of H.264/AVC, starting with low bit-rate Internet streaming applications to HDTV broadcast and Wenger, et al Expires November 15, 2008 [Page 3] Internet-Draft RTP Payload Format for SVC Video May 2008 Digital Cinema with nearly lossless coding and requiring dozens or hundreds of MBit/s. This memo defines a backwards compatible enhancement to the H264/AVC payload format [RFC3984], in which the specific features introduced by SVC are taken into account. [Edt. Note (AE): Review backwards compatibility assertion, and qualify, when memo is completed.] Specifically, it documents the enhancements relevant from an RTP transport viewpoint, and defines signaling support for SVC, including a new media subtype name. 2. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119]. This specification uses the notion of setting and clearing a bit when bit fields are handled. Setting a bit is the same as assigning that bit the value of 1 (On). Clearing a bit is the same as assigning that bit the value of 0 (Off). 3. The SVC Codec 3.1. Overview SVC defines a coded video representation in which a given bitstream offers representations of the source material at different levels of fidelity (hence the term "scalable"). Scalable video coding bitstreams, or scalable bitstreams, are constructed in a pyramidal fashion: the coding process creates bitstream components that improve the fidelity of hierarchically lower components. The fidelity dimensions offered by SVC are spatial (picture size), quality (or Signal-to-Noise Ratio - SNR), as well as temporal (pictures per second). Bitstream components associated with a given level of spatial, quality, and temporal fidelity are identified using corresponding parameters in the bitstream: dependency_id, quality_id, and temporal_id (see also Section 3.3). The fidelity identifiers have integer values, where higher values designate components that are higher in the hierarchy. It is noted that SVC offers significant flexibility in terms of how an encoder may choose to structure the dependencies between the various components. Decoding of a particular component requires the availability of all the components it depends upon, either directly, or indirectly. An operation point of an SVC bitstream consists of the bistream components required to Wenger, et al Expires November 15, 2008 [Page 4] Internet-Draft RTP Payload Format for SVC Video May 2008 be able to decode a particular dependency_id, quality_id, and temporal_id combination. SVC maintains the bitstream organization introduced in H.264/AVC. Specifically, all bitstream components are encapsulated in Network Abstraction Layer (NAL) units which are organized as Access Units (AU). An AU is associated with a single sampling instance in time. A subset of the NAL unit types correspond to the Video Coding Layer (VCL), and contain the coded picture data associated with the source content. Coded picture data at the various fidelity dimensions are organized in slices. Within one AU, a coded picture of an operation point consists of all the coded slices required for decoding up to the particular combination of dependency_id and quality_id values at the time instance corresponding to the AU. The NAL encapsulates each slice generated by the VCL into one or more NAL units. Please consult RFC 3984 for a more in-depth discussion of the NAL unit concept. SVC specifies the decoding order of NAL units. It is noted that the concept of temporal scalability is already present in H.264/AVC as profiles defined in Annex A of [H.264] already support it. Specifically, in [H.264] sub-sequences have been introduced in order to allow optional use of temporal layers. SVC extends this approach by exposing the temporal scalability information using the temporal_id parameter, alongside the dependency_id and quality_id values that are used for spatial and quality scalability. For coded picture data defined in Annex G of [SVC] this is accomplished by using a new type of NAL unit where the fidelity parameters are part of its header. For coded picture data that follow H.264/AVC, and to ensure compatibility with existing H.264/AVC receivers, a new type of "prefix" NAL unit has been defined to carry this header information. This prefix NAL unit type is among those ignored by H.264/AVC receivers as explained in [RFC3984]. Within an AU, the VCL NAL units associated with a given dependency_id and quality_id are referred to as a "layer representation". The layer representation corresponding to the lowest values of dependency_id and quality_id (i.e., zero) is the base layer representation and is compliant by design to H.264/AVC. The set of VCL and associated non-VCL NAL units across all AUs in a bitstream associated with a particular combination of values of dependency_id and quality_id, and regardless of the value of temporal_id, is conceptually a scalable layer. Due to the backwards compatibility with H.264/AVC, it is important to differentiate however whether or not SVC-specific NAL units are present in a given bitstream or not. This is particularly important for the lowest fidelity values in terms of dependency_id and quality_id (zero for both), as the corresponding VCL data are compliant to H.264/AVC, and may or may not Wenger, et al Expires November 15, 2008 [Page 5] Internet-Draft RTP Payload Format for SVC Video May 2008 be accompanied by associated prefix NAL units. This memo therefore uses the term "AVC base layer" to designate the layer that contains only H.264/AVC VCL NAL units, and "SVC base layer" to designate the same layer but with the addition of the associated SVC prefix NAL units. Note that the SVC specification [SVC] uses the term "base layer" for what in this memo will be referred to as "AVC base layer". Similarly, it is also important to be able to differentiate, within a layer, the temporal fidelity components it contains. This memo uses the term "T0" to indicate, within a particular layer, the subset that contains the NAL units associated with temporal_id equal to 0. The term "layer" is used in various contexts in this memo. For example, in the terms "Video Coding Layer" and "Network Abstraction Layer" it refers to conceptual organization levels. When referring to bitstream syntax elements such as block layer or macroblock layer, it refers to hierarchical bitstream structure levels. When used in the context of bitstream scalability, e.g., "AVC base layer", it refers to a level of representation fidelity of the source signal with a specific set of NAL units included. The correct interpretation is supported by providing the appropriate context. SNR scalability in SVC is offered in two different ways. In what is called Coarse-Grained Scalability (CGS), scalability is provided by including or excluding a complete layer when decoding a particular bitstream. In contrast, in Medium-Grained Scalability (MGS), scalability is provided by selectively omitting the decoding of specific NAL units belonging to MGS layers. The selection of the NAL units to omit can be based on fixed length fields in the NAL unit header. 3.2. Parameter Set Concept The parameter set concept is inherited from [H.264]. Please refer to section 1.2 of RFC 3984 for more details. SVC introduced a new type of sequence parameter set, referred to as a subset sequence parameter set. Subset sequence parameter sets have NAL unit type equal to 15, which is different from the NAL unit type value (7) of sequence parameter set. VCL NAL units of NAL unit type 1 to 5 must only (indirectly) refer to sequence parameter sets, while VCL NAL units of NAL unit type 20 must only (indirectly) refer to subset sequence parameter sets. Subset sequence parameter sets use a separate identifier value space than sequence parameter sets. In SVC, coded picture data from different layers may use the same or different sequence and picture parameter sets. At any time instant during the decoding process there may be one active sequence Wenger, et al Expires November 15, 2008 [Page 6] Internet-Draft RTP Payload Format for SVC Video May 2008 parameter set (for the layer representation with the highest value of (dependency_id * 16 + quality_id)) and one or more active layer SVC sequence parameter set(s) (for layer representations with lower values of (dependency_id * 16 + quality_id)). The active sequence parameter set or an active layer SVC sequence parameter set remains unchanged throughout a coded video sequence in the scalable layer in which the active sequence parameter set or active layer SVC sequence parameter set is referred to. This means that the referred sequence parameter set or subset sequence parameter set can only change at IDR access units for any layer. At any time instant during the decoding process there may be one active picture parameter set (for the layer representation with the highest value of (dependency_id * 16 + quality_id)) and one or more active layer picture parameter set(s) (for layer representations with lower values of (dependency_id * 16 + quality_id)). The active picture parameter set or an active layer picture parameter set remains unchanged throughout a layer representation in which the active picture parameter set or active layer picture parameter set is referred to, but may change from one AU to the next. 3.3. Network Abstraction Layer Unit Header SVC NAL units of type 20 encapsulate VCL data as defined in Annex G of [SVC]. A special type of an SVC NAL unit is the prefix NAL unit (type 14) that includes descriptive information of the associated H.264/AVC VCL NAL unit (type 1 or 5) that immediately follows the prefix NAL unit. SVC extends the one-byte H.264/AVC NAL unit header by three additional octets. The header indicates the type of the NAL unit, the (potential) presence of bit errors or syntax violations in the NAL unit payload, information regarding the relative importance of the NAL unit for the decoding process, the layer identification information, and other fields as discussed below. The syntax and semantics of the NAL unit header are formally specified in [SVC], but the essential properties of the NAL unit header are summarized below. The first byte of the NAL unit header has the following format (the bit fields are the same as defined for the one-byte H.264/AVC NAL unit header, while the semantics of some fields have changed slightly, in a backward compatible way): Wenger, et al Expires November 15, 2008 [Page 7] Internet-Draft RTP Payload Format for SVC Video May 2008 +---------------+ |0|1|2|3|4|5|6|7| +-+-+-+-+-+-+-+-+ |F|NRI| Type | +---------------+ The semantics of the components of the NAL unit type octet, as specified in the H.264 specification, are described briefly below. F: 1 bit forbidden_zero_bit. H.264/AVC declares a value of 1 as a syntax violation. NRI: 2 bits nal_ref_idc. A value of '00' (in binary form) indicates that the content of the NAL unit is not used to reconstruct reference pictures for future prediction. Such NAL units can be discarded without risking the integrity of the reference pictures in the same Layer. A value greater than '00' indicates that the decoding of the NAL unit is required to maintain the integrity of reference pictures in the same Layer, or that the NAL unit contains parameter sets. Type: 5 bits nal_unit_type. This component specifies the NAL unit type as defined in table 7-1 of [SVC], and later within this memo. For a reference of all currently defined NAL unit types and their semantics, please refer to section 7.4.1 in [SVC]. In H.264/AVC, NAL unit types 14, 15 and 20 are reserved for future extensions. SVC uses these three NAL unit types. NAL unit type 14 is used for prefix NAL unit, NAL unit type 15 is used for subset sequence parameter set and NAL unit type 20 is used for coded slice in scalable extension (see section 7.4.1 in [SVC]). NAL unit types 14 and 20 indicate the presence of three additional octets in the NAL unit header, as shown below. +---------------+---------------+---------------+ |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R|I| PRID |N| DID | QID | TID |U|D|O| RR| +---------------+---------------+---------------+ R: 1 bit reserved_one_bit. Reserved bit for future extension. R MUST be equal to 1. Receivers SHOULD ignore the value of R. Wenger, et al Expires November 15, 2008 [Page 8] Internet-Draft RTP Payload Format for SVC Video May 2008 I: 1 bit idr_flag. This component specifies whether the layer representation is an instantaneous decoding refresh (IDR) layer representation (when equal to 1) or not (when equal to 0). PRID: 6 bits priority_id. This flag specifies a priority identifier for the NAL unit. A lower value of PRID indicates a higher priority. N: 1 bit no_inter_layer_pred_flag. This flag specifies, when present in a coded slice NAL unit, whether inter-layer prediction may be used for decoding the coded slice (when equal to 1) or not (when equal to 0). DID: 3 bits dependency_id. This component indicates the inter-layer coding dependency level of a layer representation. At any access unit, a layer representation with a given dependency_id may be used for inter-layer prediction for coding of a layer representation with a higher dependency_id, while a layer representation with a given dependency_id shall not be used for inter-layer prediction for coding of a layer representation with a lower dependency_id. QID: 4 bits quality_id. This component indicates the quality level of an MGS layer representation. At any access unit and for identical dependency_id values, a layer representation with quality_id equal to ql uses a layer representation with quality_id equal to ql-1 for inter-layer prediction. TID: 3 bits temporal_id. This component indicates the temporal level of a layer representation. The temporal_id is associated with the frame rate, with lower values of _temporal_id corresponding to lower frame rates. A layer representation at a given temporal_id typically depends on layer representations with lower temporal_id values, but it never depends on layer representations with higher temporal_id values. U: 1 bit use_ref_base_pic_flag. A value of 1 indicates that only reference base pictures are used during the inter prediction process. A value of 0 indicates that the reference base pictures are not used during the inter prediction process. Wenger, et al Expires November 15, 2008 [Page 9] Internet-Draft RTP Payload Format for SVC Video May 2008 D: 1 bit discardable_flag. A value of 1 indicates that the current NAL unit is not used for decoding NAL units with values of dependency_id higher than the one of the current NAL unit, in the current and all subsequent access units. Such NAL units can be discarded without risking the integrity of layers with higher dependency_id values. discardable_flag equal to 0 indicates that the decoding of the NAL unit is required to maintain the integrity of layers with higher dependency_id. O: 1 bit output_flag: Affects the decoded picture output process as defined in Annex C of [SVC]. RR: 2 bits reserved_three_2bits. Reserved bits for future extension. RR MUST be equal to '11' (in binary form). Receivers SHOULD ignore the value of RR. This memo reuses the same additional NAL unit types introduced in RFC 3984, which are presented in section 6.3. In addition, this memo introduces one OPTIONAL NAL unit type, 30, as specified in section 6.9. . These NAL unit types are marked as unspecified in [SVC] and intentionally reserved for use in systems specifications like this memo. Moreover, this specification extends the semantics of F, NRI, I, PRID, DID, QID, TID, U, and D as described in section 6.4. 4. Scope This payload specification can only be used to carry the "naked" NAL unit stream over RTP, and not the byte stream format according to Annex B of [SVC]. The likely applications of this specification will be in the IP based multimedia communications fields including conversational multimedia, video telephony or video conferencing, Internet streaming and TV over IP. This specification allows, in a given RTP stream, to encapsulate NAL units belonging to o the T0 AVC base layer or the T0 SVC base layer only, as detailed in [RFC3984], or o one or more enhancement layers, or o the T0 SVC base layer, and one or more enhancement layers Wenger, et al Expires November 15, 2008 [Page 10] Internet-Draft RTP Payload Format for SVC Video May 2008 Session multiplexing SHOULD be used when different receivers in the multicast session may request different operation points of the scalable bitstream. In session multiplexing, layers are carried in multiple RTP sessions, and each RTP session is associated with one RTP stream. The RTP stream in each RTP session MAY carry one or more layers, which can be any of the above three. When each operation point corresponding to a layer may be required by some receivers, then each Layer SHOULD be carried in its own RTP stream and its own RTP session. When fewer operation points are required by the receivers, then multiple layers MAY be encapsulated within one RTP stream in one RTP session. Informative note: Layered multicast is a term commonly used to describe the application where multicast is used to transmit data that has been encapsulated into more than one RTP session using session multiplexing. This application allows different receivers in the multicast session to receive different operation points of the scalable bitstream. Layered multicast, among other application examples, is discussed in more detail in the informative Section 13.2. . When session multiplexing is not used, the following applies. o When an H.264/AVC compatible subset of the SVC base layer is transmitted, the subset SHOULD be carried in one RTP stream that MUST be encapsulated according to RFC 3984. This way, a legacy RFC 3984 receiver will be able to receive the H.264/AVC compatible bitstream subset. o When a set of layers including one or more SVC enhancement layers is transmitted, the set SHOULD be carried in one RTP stream that SHOULD be encapsulated according to this memo. This RTP payload specification is designed to be unaware of the octet string in the NAL unit payload defined in [SVC]. The NAL unit header defined in [SVC] co-serves as the payload header of this RTP payload format, when single NAL unit packetization is used, i.e. one NAL unit per RTP packet. In this case, the payload of a NAL unit follows immediately. Additionally to [RFC3984], this memo locally defines a NAL unit type in the unspecified NAL unit type space of [SVC]. If other than the single NAL unit packetization mode is used as defined in [RFC3984] or this memo, locally defined NAL unit types may be additionally present in the RTP packets, together with one or more NAL unit types as specified in [SVC]. Wenger, et al Expires November 15, 2008 [Page 11] Internet-Draft RTP Payload Format for SVC Video May 2008 5. Definitions and Abbreviations 5.1. Definitions 5.1.1. Definitions Per SVC Specification This document uses the definitions of [SVC]. The following terms, defined in [SVC], are summed up for convenience: access unit: A set of NAL units always containing exactly one primary coded picture. In addition to the primary coded picture, an access unit may also contain one or more redundant coded pictures, one auxiliary coded picture, or other NAL units not containing slices or slice data partitions of a coded picture. The decoding of an access unit always results in a decoded picture. base layer: A bitstream subset that contains all the NAL units with the nal_unit_type syntax element equal to 1 and 5 of the bitstream and does not contain any NAL unit with the nal_unit_type syntax element equal to 14, 15, or 20 and conforms to one or more of the profiles specified in Annex A of [H.264]. base quality layer representation: The layer representation of the target dependency representation of an access unit that is associated with the quality_id syntax element equal to 0. coded video sequence: A sequence of access units that consists, in decoding order, of an IDR access unit followed by zero or more non-IDR access units including all subsequent access units up to but not including any subsequent IDR access unit. dependency representation: A subset of VCL NAL units within an access unit that are associated with the same value of the dependency_id syntax element, which is provided as part of the NAL unit header or by an associated prefix NAL unit. A dependency representation consist of one or more layer representations. IDR access unit: An access unit in which the primary coded picture is an IDR picture. IDR picture: A coded picture in which all slices of the target dependency representation within the access unit are I or EI slices that causes the decoding process to mark all reference pictures as "unused for reference" immediately after decoding the IDR picture. After the decoding of an IDR picture all following Wenger, et al Expires November 15, 2008 [Page 12] Internet-Draft RTP Payload Format for SVC Video May 2008 coded pictures in decoding order can be decoded without inter prediction from any picture decoded prior to the IDR picture. The first picture of each coded video sequence is an IDR picture. layer representation: A subset of VCL NAL units within an access unit that are associated with the same values of the dependency_id and quality_id syntax elements, which are provided as part of the VCL NAL unit header or by an associated prefix NAL unit. One or more layer representations represent a dependency representation. prefix NAL unit: A NAL unit with nal_unit_type equal to 14 that immediately precedes in decoding order a NAL unit with nal_unit_type equal to 1, 5, or 12. The NAL unit that immediately succeeds in decoding order the prefix NAL unit is referred to as the associated NAL unit. The prefix NAL unit contains data associated with the associated NAL unit, which are considered to be part of the associated NAL unit. reference base picture: A reference picture that is obtained by decoding a base quality layer representation with the nal_ref_idc syntax element not equal to 0 and the store_ref_base_pic_flag syntax element equal to 1 of an access unit and all layer representations of the access unit that are referred to by inter- layer prediction of the base quality layer representation. A reference base picture is not an output of the decoding process, but the samples of a reference base picture may be used for inter prediction in the decoding process of subsequent pictures in decoding order. Reference base picture is a collective term for a reference base field or a reference base frame. scalable bitstream: A bitstream with the property that one or more bitstream subsets that are not identical to the scalable bitstream form another bitstream that conforms to the SVC specification[SVC]. target dependency representation: The dependency representation of an access unit that is associated with the largest value of the dependency_id syntax element for all dependency representations of the access unit. target layer representation: The layer representation of the target dependency representation of an access unit that is associated with the largest value of the quality_id syntax element for all layer representations of the target dependency representation of the access unit. Wenger, et al Expires November 15, 2008 [Page 13] Internet-Draft RTP Payload Format for SVC Video May 2008 5.1.2. Definitions Local to This Memo anchor layer representation: An anchor layer representation is such a layer representation that, if decoding of the operation point corresponding to the layer starts from the access unit containing this layer representation, all the following layer representations of the layer, in output order, can be correctly decoded. An anchor layer representation is a random access point to the layer the anchor layer representation belongs to. However, some layer representations, succeeding an anchor layer representation in decoding order but preceding the anchor layer representation in output order, may refer to earlier layer representations for inter prediction, and hence may not be correctly decoded if random access is performed at the anchor layer representation. AVC base layer: The subset of the SVC base layer in which all prefix NAL units (type 14) are removed. Note that this is equivalent to the term "base layer" as defined in Annex G of [SVC]. base RTP session: The RTP session, among all the RTP sessions using session multiplexing, that carries the RTP stream containing the T0 AVC base layer or the T0 SVC base layer, and zero or more enhancement layers. This RTP session does not depend on any other RTP session as indicated by mechanisms defined in [I-D.ietf-mmusic-decoding-dependency]. The base RTP session may carry NAL units of NAL unit type equal to 14 and 15. enhancement RTP session: An RTP session, among all the RTP sessions using session multiplexing, that is not the base RTP session. An enhancement RTP session typically contains an RTP stream that depends on at least one other RTP session as indicated by mechanisms defined in [I-D.ietf-mmusic-decoding- dependency]. A lower RTP session to an enhancement RTP session is an RTP session which the enhancement RTP session depends on. The lowest RTP session for a receiver is the RTP session that does not depend on any other RTP session received by the receiver. The highest RTP session for a receiver is the RTP session which no other RTP session received by the receiver depends on. cross-session decoding order number (CS-DON): A derived variable indicating NAL unit decoding order number over all NAL units within all the session-multiplexed RTP sessions that carry the same SVC bitstream. Wenger, et al Expires November 15, 2008 [Page 14] Internet-Draft RTP Payload Format for SVC Video May 2008 enhancement layer: A layer in which at least one of the values of dependency_id or quality_id is higher than 0, or a layer in which none of the NAL units is associated with the value of temporal_id equal to 0. An operation point constructed using the maximum temporal_id, dependency_id, and quality_id values associated with an enhancement layer may or may not conform to one or more of the profiles specified in Annex A of [H.264]. H.264/AVC compatible: A biststream subset that conforms to one or more of the profiles specified in Annex A of [H.264]. intra layer representation: A layer representation that contains only slices that use intra prediction, and hence do not refer to any earlier layer representation in decoding order in the same layer. Note that in [SVC] intra prediction includes intra-layer intra prediction as well as inter-layer intra prediction. layer: A bistream subset in which all NAL units of type 1, 5, 12, 14, or 20 have the same values of dependency_id and quality_id, either directly through their NAL unit header (for NAL units of type 14 or 20) or through association to a prefix (type 14) NAL unit (for NAL unit types 1, 5, or 12). A layer may contain NAL units associated with more than one values of temporal_id. operation point: An operation point is identified by a set of values of temporal_id, dependency_id, and quality_id. A bistream corresponding to an operation point can be constructed by removing all NAL units associated with a higher value of dependency_id, and all NAL units associated with the same value of dependency_id but higher values of quality_id or temporal_id. Additional NAL units may be removed (with lower dependency_id or same dependency_id but lower quality_id) if they are not required for decoding the bitstream at the particular operation point. An operation point bitstream conforms to at least one of the profiles defined in Annex A or Annex G of [SVC], and offers a representation of the original video signal at a certain fidelity. [Ed.Note(YkW): Need to check whether a bitstream subset with those additional NAL units removed is a conforming bitstream.] operation point representation: The set of all NAL units of an operation point within the same access unit. RTP packet stream: A sequence of RTP packets with increasing sequence numbers (except for wrap-around), identical PT and identical SSRC (Synchronization Source), carried in one RTP Wenger, et al Expires November 15, 2008 [Page 15] Internet-Draft RTP Payload Format for SVC Video May 2008 session. Within the scope of this memo, one RTP packet stream is utilized to transport one or more layers. session multiplexing: The SVC bitstream is distributed onto different RTP sessions, whereby each RTP session carries a single RTP packet stream. Each RTP session requires a separate signaling and has a separate Timestamp, Sequence Number, and SSRC space. Timestamps for the RTP sessions SHALL be derived from the same clock instance. Dependency between sessions MUST be signaled according to [I-D.ietf-mmusic-decoding-dependency] and this memo. SVC base layer: The layer that includes all NAL units associated with dependency_id and quality_id values both equal to 0, including prefix NAL units (NAL unit type 14). SVC enhancement layer: A layer in which at least one of the values of dependency_id or quality_id is higher than 0. An operation point constructed using the maximum dependency_id and quality_id values and any temporal_id value associated with an SVC enhancement layer does not conform to any of the profiles specified in Annex A of [H.264]. SVC NAL unit: A NAL unit of NAL unit type 14, 15, or 20 as specified in Annex G of [SVC]. SVC NAL unit header: A four-byte header resulting from the addition of a three-byte SVC-specific header extension added in NAL unit types 14, 15 and 20. SVC RTP session: Either the base RTP session or an enhancement RTP session. T0 AVC base layer: A subset of the AVC base layer constructed by removing all VCL NAL units associated with temporal_id values higher than 0. T0 SVC base layer: A subset of the SVC base layer constructed by removing all VCL NAL units associated with temporal_id values higher than 0 as well as their associated prefix NAL units. 5.2. Abbreviations In addition to the abbreviations defined in [RFC3984], the following ones are defined. Wenger, et al Expires November 15, 2008 [Page 16] Internet-Draft RTP Payload Format for SVC Video May 2008 CGS: Coarse-Grain Scalability CS-DON: Cross-Session Decoding Order Number MGS: Medium-Grain Scalability PACSI: Payload Content Scalability Information SVC: Scalable Video Coding 6. RTP Payload Format 6.1. Design Principles The following design principles have been observed: o Backward compatibility with [RFC3984] wherever possible. o The SVC base layer or any H.264/AVC compatible subset of the SVC base layer, when transmitted in its own RTP stream, MUST be encapsulated using [RFC3984]. This ensures that such an RTP stream can be understood by RFC 3984 legacy receivers. o MANEs are signaling aware and rely on signaling information. MANEs have state. o MANEs can aggregate multiple RTP streams, possibly from multiple RTP sessions. o MANEs can perform media-aware stream thinning. By using the payload header information identifying Layers within an RTP session, MANEs are able to remove packets from the incoming RTP packet stream. This implies rewriting the RTP headers of the outgoing packet stream and rewriting of RTCP Receiver Reports. 6.2. RTP Header Usage Please see section 5.1 of [RFC3984]. 6.3. Common Structure of the RTP Payload Format Please see section 5.2 of [RFC3984]. 6.4. NAL Unit Header Usage The structure and semantics of the NAL unit header were introduced in section 3.3. . This section specifies the semantics of F, NRI, I, PRID, DID, QID, TID, U, and D according to this specification. The semantics of F specified in section 5.3 of [RFC3984] also applies herein. Wenger, et al Expires November 15, 2008 [Page 17] Internet-Draft RTP Payload Format for SVC Video May 2008 For NRI, for the bitstream conforming to one of the profiles defined in Annex A of [H.264] and transported using [RFC3984], the semantics specified in section 5.3 of [RFC3984] are applicable, i.e., NRI also indicates the relative importance of NAL units. In an SVC context, in addition to the semantics specified in Annex G of [SVC], NRI also indicates the relative importance of NAL units within a layer. [Edt. Note (YkW): "SVC context" to be clearly specified.] For I, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to protect NAL units with I equal to 1 better than NAL units with I equal to 0. MANEs MAY also utilize information of NAL units with I equal to 1 to decide when to forward more packets for an RTP packet stream. For example, when it is sensed that spatial layer switching has happened such that the operation point has changed to a higher value of DID, MANEs MAY start to forward NAL units with the higher value of DID only after forwarding a NAL unit with I equal to 1 with the higher value of DID. Note that, in the context of this section, "protecting a NAL unit" means any RTP or network transport mechanism that could improve the probability of success delivery of the packet conveying the NAL unit, including applying a QoS-enabled network, Forward Error Correction (FEC), retransmissions, and advanced scheduling behavior, whenever possible. For PRID, the semantics specified in Annex G of [SVC] applies. Note, that MANEs implementing unequal error protection MAY use this information to protect NAL units with smaller PRID values better than those with larger PRID values, for example by including only the more important NAL units in an FEC protection mechanism. The importance for the decoding process decreases as the PRID value increases. For DID, QID, TID, in addition to the semantics specified in Annex G of [SVC], according to this memo, values of DID, QID, or TID indicate the relative importance in their respective dimension. A lower value of DID, QID, or TID indicates a higher importance if the other two components are identical. MANEs MAY use this information to protect more important NAL units better than less important NAL units. For U, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to protect NAL units with U equal to 1 better than NAL units with U equal to 0. For D, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to determine whether a given NAL unit is required for successfully decoding a Wenger, et al Expires November 15, 2008 [Page 18] Internet-Draft RTP Payload Format for SVC Video May 2008 certain Operation Point of the SVC bitstream, hence to decide whether to forward the NAL unit. 6.5. Packetization Modes Section 5.4 of RFC 3984 applies when session multiplexing is not in use. The packetization modes specified in Section 5.4 of RFC 3984 are also referred to as session-specific packetization modes. When session multiplexing is in use, the following applies in addition. 6.5.1. Packetization Modes for Session Multiplexing This memo specifies four cases of session-multiplexing packetization modes when session multiplexing is in use: o Non-interleaved timestamp based (NI-T) mode o Non-interleaved CS-DON based (NI-C) mode o Non-interleaved combined timestamp and CS-DON (NI-TC) mode o Interleaved CS-DON (I-C) mode The NI-T, NI-C, and NI-TC modes are targeted for systems that require relatively low end-to-end latency, e.g. conversational systems. In the NI-T, NI-C, and NI-TC modes, NAL units in each RTP session are transmitted in NAL unit decoding order. [Ed.Note(YkW): Add more introductions for each of the NI-T, NI-C and NI-TC modes.] The I-C mode is targeted for systems that do not require very low end-to-end latency. The I-C mode allows transmission of NAL units out of NAL unit decoding order in each RTP session. The session-multiplexing packetization mode in use MAY be signaled by the value of the OPTIONAL session-multiplexing-packetization-mode media type parameter or by external means. When the value of session-multiplexing-packetization-mode is equal to 0, the NI-T mode MUST be used. When the value of session-multiplexing-packetization- mode is equal to 1, the NI-C mode MUST be used. When the value of session-multiplexing-packetization-mode is equal to 2 or session- multiplexing-packetization-mode is not present, the NI-TC mode MUST be used. When the value of session-multiplexing-packetization-mode is equal to 3, the I-C mode MUST be used. [Ed.Note(YkW): There MAY be at most one global session-multiplexing-packetization-mode present in the SDP common for all the multiplexed RTP sessions. It is also possible to have session-multiplexing-packetization-mode session- Wenger, et al Expires November 15, 2008 [Page 19] Internet-Draft RTP Payload Format for SVC Video May 2008 specific in the SDP, but then all the multiplexed sessions MUST have the same value of this parameter. When session-multiplexing- packetization-mode is not present, the NI-TC mode is implied.] The used session-multiplexing packetization mode governs which session-specific packetization modes are allowed in the multiplexed RTP sessions, which in turn govern which NAL unit types are allowed as RTP payloads. Table 3.1 summarizes the allowed session-specific packetization modes for the NI-T, NI-C and NI-TC session-multiplexing packetization modes. Table 3.2 summarizes the allowed session-specific packetization modes for the I-C session-multiplexing packetization mode. Table 3.1 Summary of allowed session-specific packetization modes for the NI-T, NI-C and NI-TC session-multiplexing packetization modes (yes = allowed, no = disallowed) Session-Specific Mode Base Session Enhancement Session ---------------------------------------------------------- Single NAL Unit Mode yes no Non-Interleaved Mode yes yes Interleaved Mode no no Table 3.2 Summary of allowed session-specific packetization modes for the I-C session-multiplexing packetization mode (yes = allowed, no = disallowed) Session-Specific Mode Base Session Enhancement Session ---------------------------------------------------------- Single NAL Unit Mode no no Non-Interleaved Mode no no Interleaved Mode yes yes Table 3.3 summarizes the allowed NAL unit types for each allowed session-specific packetization mode of the NI-T session-multiplexing packetization mode. Table 3.4 summarizes the allowed NAL unit types for each allowed session-specific packetization mode of the NI-C and NI-TC session-multiplexing packetization modes. Table 3.5 summarizes the allowed NAL unit types for the only allowed session-specific packetization mode (i.e. the interleaved mode) of the I-C session- multiplexing packetization mode. Wenger, et al Expires November 15, 2008 [Page 20] Internet-Draft RTP Payload Format for SVC Video May 2008 Table 3.3 Summary of allowed NAL unit types for each session- specific packetization mode of the NI-T session-multiplexing packetization mode (yes = allowed, no = disallowed, ig = ignore) Type Packet Single NAL Non-Interleaved Unit Mode Mode ------------------------------------------------ 0 undefined ig ig 1-23 NAL unit yes yes 24 STAP-A no yes 25 STAP-B no no 26 MTAP16 no no 27 MTAP24 no no 28 FU-A no yes 29 FU-B no no 30 PACSI no no 31 undefined ig ig Table 3.4 Summary of allowed NAL unit types for each session- specific packetization mode of the NI-C and NI-TC session- multiplexing packetization modes (yes = allowed, no = disallowed, ig = ignore) Type Packet Single NAL Non-Interleaved Unit Mode Mode ------------------------------------------------ 0 undefined ig ig 1-23 NAL unit yes yes 24 STAP-A no yes 25 STAP-B no no 26 MTAP16 no no 27 MTAP24 no no 28 FU-A no yes 29 FU-B no no 30 PACSI yes yes 31 undefined ig ig Wenger, et al Expires November 15, 2008 [Page 21] Internet-Draft RTP Payload Format for SVC Video May 2008 Table 3.5 Summary of allowed NAL unit types for the session-specific packetization mode of the I-C session-multiplexing packetization mode (yes = allowed, no = disallowed, ig = ignore) Type Packet Interleaved Mode ------------------------------ 0 undefined ig 1-23 NAL unit no 24 STAP-A no 25 STAP-B yes 26 MTAP16 yes 27 MTAP24 yes 28 FU-A yes 29 FU-B yes 30 PACSI no 31 undefined ig The NAL unit type values indicated as undefined in Tables 3.3, 3.4 and 3.5 are reserved for future extensions. NAL units of those types SHOULD NOT be sent by a sender and MUST be ignored by a receiver. Note that NAL unit type 30 is indicated as undefined in RFC 3984, therefore RFC 3984 receivers MUST ignore NAL units of this type, if present. 6.6. Decoding Order Number (DON) Section 5.5 of [RFC3984] applies when session multiplexing is not in use. When session multiplexing is in use, the following applies in addition. 6.6.1. Cross-Session DON (CS-DON) for Session Multiplexing When the NI-C or NI-TC session-multiplexing packetization mode is in use, the packetization of each session MUST be as specified in Section 7.1. , and the following applies for the derivation of the CS-DON value for each non-PACSI NAL unit. Wenger, et al Expires November 15, 2008 [Page 22] Internet-Draft RTP Payload Format for SVC Video May 2008 o For each non-PACSI NAL unit carried in a session using the single NAL unit session-specific packetization mode, the CS-DON value of the NAL unit is equal to (DONC_prev_PACSI + SN_diff - 1) % 65536, wherein '%' stands for modulo operation, DONC_prev_PACSI is the DONC value of the previous PACSI NAL unit with the same NALU time as the current NAL unit, and SN_diff is calculated as follows (assuming that the SN values of the current NAL unit and the previous PACSI NAL unit with the same NALU time as the current NAL unit are SN1 and SN2, respectively). If SN1 > SN2, SN_diff = SN1 - SN2 Else SN_diff = SN2 + 65536 - SN1 o For non-PACSI NAL units carried in a session using the non- interleaved session-specific packetization mode, the CS-DON value of each non-PACSI NAL unit is derived as follows. For a non-PACSI NAL unit in a single NAL unit packet, the following applies. If the previous PACSI NAL unit is contained in a single NAL unit packet, the CS-DON value of the NAL unit is calculated as above when the single NAL unit session- specific packetization mode is in use; Otherwise (the previous PACSI NAL unit is contained in an STAP-A packet), the CS-DON value of the NAL unit is equal to (the CS-DON value of the previous non-PACSI NAL unit in decoding order + 1) % 65536, wherein '%' stands for modulo operation. For a non-PACSI NAL unit in an STAP-A packet, the following applies. If the non-PACSI NAL unit is the first non-PACSI NAL unit in the STAP-A packet, the CS-DON value of the NAL unit is equal to DONC of the PACSI NAL unit in the STAP-A packet; Otherwise (the non-PACSI NAL unit is not the first non- PACSI NAL unit in the STAP-A packet), the CS-DON value of the NAL unit is equal to (the CS-DON value of the previous non-PACSI NAL unit in decoding order + 1) % 65536, wherein '%' stands for modulo operation. Wenger, et al Expires November 15, 2008 [Page 23] Internet-Draft RTP Payload Format for SVC Video May 2008 For a non-PACSI NAL unit in a number of FU-A packets, the CS- DON value of the NAL unit is calculated as above when the single NAL unit session-specific packetization mode is in use, with SN1 being the SN value of the start FU-A packet. When the I-C session-multiplexing packetization mode is in use, the DON values derived according to RFC 3984 of all the NAL units in each of the multiplexed RTP sessions MUST indicate CS-DON values. 6.7. Aggregation Packets Please see section 5.7 of [RFC3984]. 6.8. Fragmentation Units (FUs) Please see section 5.8 of [RFC3984]. 6.9. Payload Content Scalability Information (PACSI) NAL Unit A new NAL unit type is specified in this memo, and referred to as payload content scalability information (PACSI) NAL unit. The OPTIONAL PACSI NAL unit, if present, MUST be the first NAL unit in an aggregation packet or the NAL unit in a single NAL unit packet, and it MUST NOT be present in other types of packets. The PACSI NAL unit, when included in an aggregation packet, indicates scalability information and other characteristics that are common for all the remaining NAL units in the payload of the aggregation packet. Furthermore, a PACSI NAL unit MAY contain zero or more SEI NAL units. PACSI NAL unit makes it easier for MANEs to decide whether to forward/process/discard the aggregation packet containing the PACSI NAL unit. Other reasons to use PACSI NAL units are explained later when specifying the semantics of the fields. Senders MAY create PACSI NAL units and receivers MAY ignore them, or use them as hints to enable efficient aggregation packet processing or decoding order recovery in session multiplexing. Note that the NAL unit type for the PACSI NAL unit is selected among those values that are unspecified in [SVC] and [RFC3984]. When the first aggregation unit of an aggregation packet contains a PACSI NAL unit, there MUST be at least one additional aggregation unit present in the same packet. The RTP header and payload header fields of the aggregation packet are set according to the remaining NAL units in the aggregation packet. When a PACSI NAL unit is included in a multi-time aggregation packet (MTAP), the decoding order number (DON) for the PACSI NAL unit MUST be set to indicate that the PACSI NAL unit has an identical DON to Wenger, et al Expires November 15, 2008 [Page 24] Internet-Draft RTP Payload Format for SVC Video May 2008 the first NAL unit in decoding order among the remaining NAL units in the aggregation packet. When a PACSI NAL unit is included in a single NAL unit packet, the RTP header and payload header fields of the packet are set according to the next non-PACSI NAL unit in transmission order. The structure of a PACSI NAL unit is as follows. The first four octets are exactly the same as the four-byte SVC NAL unit header as discussed in section 3.3. . They are followed by one always present octet, five optional octets, and zero or more SEI NAL units, each SEI NAL unit preceded by a 16-bit unsigned size field (in network byte order) that indicates the size of the following NAL unit in bytes (excluding these two octets, but including the NAL unit type octet of the SEI NAL unit). Figure 1 illustrates the PACSI NAL unit structure and an example of a PACSI NAL unit containing two SEI NAL units. The bits A, P, C, S, and E are specified only if the bit X is equal to 1. The fields TL0PICIDX and IDRPICID are present only if the bit Y is equal to 1. The fields TL0PICIDX and IDRPICID MUST NOT be present if the bit Y is equal to 0. The field DONC is present only if the bit T is equal to 1. The field T MUST be equal to 0 if the aggregation packet containing the PACSI NAL unit is not an STAP-A packet. Wenger, et al Expires November 15, 2008 [Page 25] Internet-Draft RTP Payload Format for SVC Video May 2008 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F|NRI| Type |R|I| PRID |N| DID | QID | TID |U|D|O| RR| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|Y|T|A|P|C|S|E| TL0PICIDX (o.)| IDRPICID (o.) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DONC (o.) | NAL unit size 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SEI NAL unit 1 | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | NAL unit size 2 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | SEI NAL unit 2 | | +-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 PACSI NAL unit structure. Fields suffixed by "(o.)" are OPTIONAL. The values of the fields in PACSI NAL unit MUST be set as follows. The term "target NAL unit" is used in the semantics of some fields. When the PACSI NAL unit is included in an aggregation packet, a "target NAL unit" refers to one or more NAL units that are contained in the aggregation packet, but not included in the PACSI NAL unit itself, that are in the same access unit as the first NAL unit following the PACSI NAL unit in the aggregation packet. When the PACSI NAL unit is included in a single NAL unit packet, a "target NAL unit" refers to the next non-PACSI NAL unit in transmission order. o The F bit MUST be set to 1 if the F bit in at least one of the remaining NAL units in the payload of the aggregation packet is equal to 1 (when the PACSI NAL unit is included in an aggregation packet) or if the next non-PACSI NAL unit in transmission order has the F bit equal to 1 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the F bit MUST be set to 0. o The NRI field MUST be set to the highest value of NRI field among all the remaining NAL units in the payload of the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or the value of the NRI field of the next non-PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). Wenger, et al Expires November 15, 2008 [Page 26] Internet-Draft RTP Payload Format for SVC Video May 2008 o The Type field MUST be set to 30. o The R bit MUST be set to 1. Receivers SHOULD ignore the value of R. o The I bit MUST be set to 1 if the I bit of at least one of the remaining NAL units in the payload of the aggregation packet is equal to 1 (when the PACSI NAL unit is included in an aggregation packet) or if the I bit of the next non-PACSI NAL unit in transmission order is equal to 1 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the I bit MUST be set to 0. o The PRID field MUST be set to the lowest value of the PRID values of all the remaining NAL units in the payload of the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or the PRID value of the next non-PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). o The N bit MUST be set to 1 if the N bit of all the remaining NAL units in the payload of the aggregation packet is equal to 1 (when the PACSI NAL unit is included in an aggregation packet) or if the N bit of the next non-PACSI NAL unit in transmission order is equal to 1 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the N bit MUST be set to 0. o The DID field MUST be set to the lowest value of the DID values of all the remaining NAL units in the payload of the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or the DID value of the next non-PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). o o The QID field MUST be set to the lowest value of the QID values of all the remaining NAL units with the lowest value of DID in the payload of the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or the QID value of the next non-PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). o The TID field MUST be set to the lowest value of the TID values of all the remaining NAL units with the lowest value of DID in the payload of the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or the TID value of the next non-PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). Wenger, et al Expires November 15, 2008 [Page 27] Internet-Draft RTP Payload Format for SVC Video May 2008 o The U bit MUST be set to 1 if the U bit of at least one of the remaining NAL units in the payload of the aggregation packet is equal to 1 (when the PACSI NAL unit is included in an aggregation packet) or if the U bit of the next non-PACSI NAL unit in transmission order is equal to 1 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the U bit MUST be set to 0. o The D bit MUST be set to 1 if the D value of all the remaining NAL unit in the payload is equal to 1 (when the PACSI NAL unit is included in an aggregation packet) or if the D bit of the next non-PACSI NAL unit in transmission order is equal to 1 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the D bit MUST be set to 0. o The O bit MUST be set to 1 if the O bit of at least one of the remaining NAL units in the payload of the aggregation packet is equal to 1 (when the PACSI NAL unit is included in an aggregation packet) or if the O bit of the next non-PACSI NAL unit in transmission order is equal to 1 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the O bit MUST be set to 0. o The RR field MUST be set to '11' (in binary form). Receivers SHOULD ignore the value of RR. o If the X bit is equal to 1, the bits A, P, and C are specified as below. Otherwise, the bits A, P, and C are unspecified, and receivers MUST ignore these bits. The X bit SHOULD be identical for all the PACSI NAL units in all the RTP sessions carrying the same SVC bitstream. o If the Y bit is equal to 1, the OPTIONAL fields TL0PICIDX and IDRPICID MUST be present and specified as below, and the bits S and E are also specified as below. Otherwise, the fields TL0PICIDX and IDRPICID MUST NOT be present, whereas the S and E bits are unspecified and receivers MUST ignore these bits. The Y bit SHOULD be identical for all the PACSI NAL units in all the RTP sessions carrying the same SVC bitstream. o If the T bit is equal to 1, the OPTIONAL field DONC MUST be present and specified as below. Otherwise, the field DONC MUST NOT be present. Wenger, et al Expires November 15, 2008 [Page 28] Internet-Draft RTP Payload Format for SVC Video May 2008 o The A bit MUST be set to 1 if all the target NAL units belong to anchor layer representations. Otherwise, the A bit MUST be set to 0. The A bit SHOULD be identical for all the PACSI NAL units for which the target NAL units belong to the same access unit. Informative note: The A bit indicates whether CGS or spatial layer switching at a non-IDR layer representation (a layer representation with nal_unit_type not equal to 5 and idr_flag not equal to 1) can be performed. When the coded pattern like IBBP is in use, non-IDR intra layer representation can be used for random access. Compared to using only IDR layer representations, higher coding efficiency can be achieved. The H.264/AVC or SVC solution to indicate the random accessibility of a non-IDR intra layer representation is using recovery point SEI message. However, with this A bit it is much easier to parse than to parse the recovery point SEI message, which may even be buried deeply in an SEI NAL unit. Furthermore, the SEI message may not be present in the bitstream. o The P bit MUST be set to 1 if all the remaining NAL units in the payload of the aggregation packet are with redundant_pic_cnt greater than 0 (when the PACSI NAL unit is included in an aggregation packet) or the next non-PACSI NAL unit in transmission order is with redundant_pic_cnt greater than 0 (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the P bit MUST be set to 0. Informative note: The P bit indicates whether a packet can be discarded because it contains only redundant slice NAL units. Without this bit, the corresponding information can be concluded from the syntax element redundant_pic_cnt, which is buried in the variable-length coded slice header. o The C bit MUST be set to 1 if all the target NAL units belong to intra layer representations. Otherwise, the C bit MUST be set to 0. The C bit SHOULD be identical for all the PACSI NAL units for which the target NAL units belong to the same access unit. Informative note: The C bit indicates whether a packet contains intra slices which may be the only packets to be forwarded for a fast forward playback, e.g. when the network condition is extremely bad. Wenger, et al Expires November 15, 2008 [Page 29] Internet-Draft RTP Payload Format for SVC Video May 2008 o The S bit MUST be set to 1, if the first VCL NAL unit, in decoding order, of the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet is present in the payload (when the PACSI NAL unit is included in an aggregation packet) or if the next non-PACSI NAL unit in transmission order is the first VCL NAL unit, in decoding order, of a layer representation (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the S bit MUST be set to 0. o The E bit MUST be set to 1, if the last VCL NAL unit, in decoding order, of the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet is present in the payload (when the PACSI NAL unit is included in an aggregation packet) or if the next non-PACSI NAL unit in transmission order is the last VCL NAL unit, in decoding order, of a layer representation (when the PACSI NAL unit is included in a single NAL unit packet). Otherwise, the E field MUST be set to 0. Informative note: The S or E bit indicates whether the first or last slice, in transmission order, of a layer representation is in a packet, to enable a MANE to detect slice loss and take proper action such as requesting a retransmission as soon as possible, as well as to allow an efficient playout buffer handling similarly as the M bit in the RTP header. The M bit in the RTP header still indicates the end of an access unit, not the end of a layer representation. o When present, the TL0PICIDX field MUST be set to equal to tl0_dep_rep_idx as specified in Annex G of [SVC] for the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or containing the next non- PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). o When present, the IDRPICID field MUST be set to equal to effective_idr_pic_id as specified in Annex G of [SVC] for the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or containing the next non- PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). Informative note: The TL0PICIDX and IDRPICID fields enable the detection of the loss of layer representations in the most important temporal layer, by receivers as well as MANEs. SVC Wenger, et al Expires November 15, 2008 [Page 30] Internet-Draft RTP Payload Format for SVC Video May 2008 includes a solution by using SEI messages, which are harder to parse and may not be present in the bitstream at all. o When present, the field DONC indicates the cross-session decoding order number (CS-DON) for the first NAL unit of the remaining NAL units in the aggregation packet (when the PACSI NAL unit is included in an aggregation packet) or the CS-DON of the next non- PACSI NAL unit in transmission order (when the PACSI NAL unit is included in a single NAL unit packet). The PACSI NAL unit SHALL include a subset (zero to all) of the SEI NAL units associated with the access unit to which the target NAL units belong, and SHALL NOT contain SEI NAL units associated with any other access unit. Informative note: Senders may repeat such SEI NAL units in the PACSI NAL unit the presence of which in more than one packet is essential for packet loss robustness. Receivers may use the repeated SEI messages in place of missing SEI messages. In H.264/AVC and SVC, within each access unit, SEI NAL units must appear before any VCL NAL unit in decoding order. Therefore, without using PACSI NAL units, SEI messages are typically only conveyed in the first packet of those packets conveying an access unit. When the PACSI NAL unit is included in an aggregation packet, an SEI message SHOULD NOT be included in the PACSI NAL unit and included in one of the remaining NAL units contained in the same aggregation packet. 7. Packetization Rules Section 6 of [RFC3984] applies. The following applies in addition. All receivers MUST support the single NAL unit packetization mode to provide backward compatibility to endpoints supporting only the single NAL unit mode of RFC 3984. However, the use of single NAL unit packetization mode (packetization-mode equal to 0) SHOULD be avoided whenever possible, because encapsulating NAL units of small sizes, e.g. small NAL units containing parameter sets or SEI messages, in their own packets is typically less efficient because of the relatively big overhead. All receivers MUST support the non-interleaved mode of [RFC3984]. Informative note: The non-interleaved mode allows an application to encapsulate a single NAL unit in a single RTP packet. Wenger, et al Expires November 15, 2008 [Page 31] Internet-Draft RTP Payload Format for SVC Video May 2008 Historically, the single NAL unit mode has been included into [RFC3984] only for compatibility with ITU-T Rec. H.241 Annex A [H.241]. There is no point in carrying this historic ballast towards a new application space such as the one provided with SVC. More technically speaking, the implementation complexity increase for providing the additional mechanisms of the non- interleaved mode (namely STAP-A and FU-A) is minor, and the benefits are great, that STAP-A and FU-A implementation is required. A NAL unit of small size SHOULD be encapsulated in an aggregation packet together with one or more other NAL units. For example, non- VCL NAL units such as access unit delimiter, parameter set, or SEI NAL unit are typically small. A prefix NAL unit and the NAL unit with which it is associated, and which follows the prefix NAL unit in decoding order, SHOULD be included in the same aggregation packet whenever an aggregation packet is used for the associated NAL unit. Informative note: When either the prefix NAL unit or the associated NAL unit containing an H.264/AVC coded slice is lost, the remaining one would be hardly useful in SVC context, wherein the prefix NAL unit must be available for decoded picture buffer management operations of the decoding process. When the first aggregation unit of an aggregation packet contains a PACSI NAL unit, there MUST be at least one additional aggregation unit present in the same packet. 7.1. Packetization Rules for Session Multiplexing When session multiplexing is used, decoding order recovery for NAL units carried in all the multiplexed RTP sessions is needed. The following packetization rules ensure that decoding order of NAL units carried in the multiplexed sessions can be correctly recovered for each of the session-multiplexing packetization modes according to the de-packetization process specified in Section 8.1. . When the NI-T or NI-TC session-multiplexing packetization mode is in use, the following applies. Wenger, et al Expires November 15, 2008 [Page 32] Internet-Draft RTP Payload Format for SVC Video May 2008 o If an access unit of sampling time instance X is present in RTP session A, this access unit MUST be also present in any RTP session, which depends on RTP session A. [Ed.Note(YkW): How additional video NAL units are added to ensure this requirement needs to be specified herein. Thomas W. also mentioned earlier an efficient way of addition of NAL units. It would be nice to have that text too - maybe not herein.] Informative note: This restriction may be achieved for pre- encoded content by inserting filler data NAL units (NAL unit type 12) as defined in [SVC]. This insertion can be achieved by encoders, servers, as well as by MANEs. o When a PACSI NAL unit is present, the T bit MUST be equal to 0, i.e. the DONC field MUST NOT be present. When the NI-C or NI-TC session-multiplexing packetization mode is in use, the following applies. o For each single NAL unit packet containing a non-PACSI NAL unit, if present, the previous packet MUST have the same RTP timestamp as the single NAL unit packet, and the following applies. If the NALU time of the non-PACSI NAL unit is not equal to the NALU time of the previous non-PACSI NAL unit in decoding order, the previous packet MUST contain a PACSI NAL unit containing the DONC field; Otherwise (the NALU time of the non-PACSI NAL unit is equal to the NALU time of the previous non-PACSI NAL unit in decoding order), the previous packet MAY contain a PACSI NAL unit containing the DONC field. o For each STAP-A packet, if present, the first NAL unit in the STAP-A packet MUST be a PACSI NAL unit containing the DONC field. o For each FU-A packet, if present, the previous packet MUST have the same RTP timestamp as the FU-A packet, and the following applies. If the FU-A packet is the start of the fragmented NAL unit, the following applies; If the NALU time of the fragmented NAL unit is not equal to the NALU time of the previous non-PACSI NAL unit in decoding order, the previous packet MUST contain a PACSI NAL unit containing the DONC field; Wenger, et al Expires November 15, 2008 [Page 33] Internet-Draft RTP Payload Format for SVC Video May 2008 Otherwise (the NALU time of the fragmented NAL unit is equal to the NALU time of the previous non-PACSI NAL unit in decoding order), the previous packet MAY contain a PACSI NAL unit containing the DONC field. Otherwise if the FU-A packet is the end of the fragmented NAL unit, the following applies. If the next non-PACSI NAL unit in decoding order has NALU time equal to the NALU time of the fragmented NAL unit, and is carried in a number of FU-A packets or a single NAL unit packet, the next packet MUST be a single NAL unit packet containing a PACSI NAL unit containing the DONC field. Otherwise (the FU-A packet is neither the start nor the end of the fragmented NAL unit), the previous packet MUST be a FU-A packet. o For each single NAL unit packet containing a PACSI NAL unit, if present, the PACSI NAL unit MUST contain the DONC field. When the I-C session-multiplexing packetization mode is in use, the following applies. o When a PACSI NAL unit is present, the T bit MUST be equal to 0, i.e. the DONC field MUST NOT be present. The following packetization rules allow flexible transmission of non- VCL NAL units in session multiplexing. [Ed.Note(YkW): Add the non- VCL NAL unit packetization rules here.] 8. De-Packetization Process For a single RTP session, the de-packetization process specified in section 7 of [RFC3984] applies [Edt. Note: with some fixes to section 7 of RFC 3984 and some changes/additions to section 7.3 (Additional De-Packetization Guidelines) of RFC 3984 - TBD]. For receiving more than one of multiple RTP sessions conveying the same scalable bitstream, the de-packetization process is specified in section 8.1. . Wenger, et al Expires November 15, 2008 [Page 34] Internet-Draft RTP Payload Format for SVC Video May 2008 8.1. De-Packetization Process for Session Multiplexing As for a single RTP session, the general concept behind these de- packetization processes is to reorder NAL units from transmission order to the NAL unit decoding order. The sessions to be received SHALL be identified by mechanisms specified in [I-D.ietf-mmusic-decoding-dependency]. Enhancement RTP sessions typically contain an RTP stream that depends on at least one other RTP session, as indicated by mechanisms defined in [I-D.ietf- mmusic-decoding-dependency]. A lower RTP session to an enhancement RTP session is an RTP session which the enhancement RTP session depends on. The lowest RTP session for a receiver is the base RTP session, which does not depend on any other RTP session received by the receiver. The highest RTP session for a receiver is the RTP session which no other RTP session received by the receiver depends on. For each of the RTP sessions, the RTP reception process as specified in RFC 3550 is applied, such that the received packets are passed in increasing order of timestamp, and, for those RTP packets with identical RTP timestamp, in increasing order of sequence number, into the payload de-packetization to NAL units as defined in this memo. The decoding order of the NAL units carried in all the multiplexed RTP sessions is then recovered by applying one of the following subsections, depending on which of the session-multiplexing packetization mode is in use. 8.1.1. Decoding Order Recovery for the NI-T and NI-TC Modes The following process SHALL be applied when the NI-T session- multiplexing packetization mode is in use. The following process MAY be applied when the NI-TC session-multiplexing packetization mode is in use. The process is based on RTP session dependency signaling, RTP sequence numbers, and timestamps. o Within each RTP stream, the decoding order of NAL units SHALL be recovered according to the following rules: When using the single NAL unit mode (packetization-mode equal to 0) or the non-interleaved mode (packetizaton mode equal to 1), the RTP header sequence number SHALL give the decoding order as specified in [RFC3984]. Wenger, et al Expires November 15, 2008 [Page 35] Internet-Draft RTP Payload Format for SVC Video May 2008 When the interleaved mode (packetization-mode equal to 2) is used, the Decoding Order Number SHALL give the decoding order as specified in [RFC3984]. Informative note: The decoding order recovery process cannot rely on timestamp increase as indicator for decoding order. o The decoding order of NAL units from multiple RTP streams in multiple RTP sessions SHALL be recovered into a single sequence of NAL units, grouped into access units, by performing the following rules: NAL units with the same (RTP or NTP) timestamp are grouped in decoding order to operation point representations in each RTP stream. Operation point representations with the same (NTP) timestamp SHALL be grouped to access units in order of the SVC RTP session dependency, from lowest to highest. Informative note: There may be operation point representations which do not have any corresponding operation point representations in RTP streams of lower SVC RTP sessions. [Edt. Note (TS): When SEI messages are not part of the base RTP session, they are not transported in decoding order. Only in that case this paragraph is required. See open issue section.] SEI messages (NAL unit type equal to 6), when present in any RTP session not equal to the base RTP session, SHALL be re- ordered so that the resulting access unit order conforms to [SVC], i.e. NAL units with nal_unit_type equal to 6 present in any of the RTP streams shall be grouped and precede directly any NAL units of type 1 , 5, 14, 15 and 20 in the access unit. The access units SHALL be passed in order of decoding order appearance of timestamps in the highest SVC RTP session to the decoder. Informative example: The example shown in Figure 2. refers to three SVC RTP sessions A, B and C. In the example, the dependency signaling as described in 9.2.3. , indicates, that Session A does not depend on any other of the sessions; B depends on A; C depends on A and B as restricted in section 7. . Session A has the lowest frame rate and Session B and C have the same, but a higher frame rate. Figure 2. shows an example for buffering with different jitter between sessions, i.e. at Wenger, et al Expires November 15, 2008 [Page 36] Internet-Draft RTP Payload Format for SVC Video May 2008 buffering startup not all packets of the same time instance are available. The process first proceeds to TS [8] and remove/ignore all preceding NAL units in each of the buffers of RTP session A,B, and C. Then starting from session C, the first timestamp available in decoding order (TS [1]) is selected and all operation point representations in lower RTP sessions A and B are moved in order of the RTP session dependency (in the example form session A -> B -> C) into the decoder. Then the next timestamp in the highest RTP session C is selected and the process described above is repeated. Note, that there may be no matching operation point representation at the lowest RTP session A, e.g. for TS[5]. In case of "real" packet loss at TS[4] and TS[2], a similar processing as described above may be applied to get synchronized with the timestamp order as given by the highest RTP session (in the example - session "C"). During an interval where losses are present in the highest RTP session, reordering may be in some cases only possible up to the highest loss- free received RTP session. Such cases may occur, when multiple losses in the highest RTP session are present and the correct order of timestamps over all the sessions cannot be recovered by any lower of the sessions than the highest RTP session. Decoding order and dependency of NAL units per received RTP session with different jitter in sessions at buffering startup time: C: ------------(1,2)-(3,4)--(5)---(6)---(7,8)(9,10)-(11)--(12)---- | | | | | | | | | | B: -(1,2)-(3,4)-(5)---(6)--(7,8)-(9,10)-(11)-(12)--(13,14)(15,15)- | | | | | | A: -------(1)---------------(2)---(3)---------------(4)----(5)---- -------------------------------------------------------------------> TS: [4] [2] [1] [3] [8] [6] [5] [7] [12] [10] Key: A, B, C - RTP sessions Integer values in '()' - NAL unit decoding order per RTP session '( )' - groups the NAL units of an operation point representation in a RTP session '|' - indicates corresponding operation point representations in the RTP sessions Integer values in '[]' - media Timestamp (TS), sampling time Figure 2 Example for session multiplexing with different jitter in session at startup Wenger, et al Expires November 15, 2008 [Page 37] Internet-Draft RTP Payload Format for SVC Video May 2008 [Ed.Note(YkW): Clean the text above and resolve the comments sent by Ye-Kui to the AVT mailing list on 6 April, 2008.] 8.1.2. Decoding Order Recovery for the NI-C, NI-TC and I-C Modes The following process SHALL be used when the NI-C or ANIT session- multiplexing packetization mode is in use. The following process MAY be applied when the NI-TC session-multiplexing packetization mode is in use. The RTP packets output from the RTP-level reception processing for each session are placed into the de-session-multiplexing buffer. [Ed.Note(YkW): Add handling of some cases of packet losses when the NI-C or NI-TC mode is in use, that discards some received NAL units for which the CS-DON value cannot be derived.] It is RECOMMENDED to set the size of the de-session-multiplexing buffer, in terms of number of bytes, equal to or greater than the value of the sprop-desemul-buf-req media type parameter of the highest RTP session the receiver receives. The CS-DON value is calculated and stored for each NAL unit. The receiver operation is described below with the help of the following functions and constants: o Function AbsDON is specified in Section 8.1 of RFC 3984. o Function don_diff is specified in Section 5.5 of RFC 3984. o Constant N is the value of the OPTIONAL sprop-session- multiplexing-depth media type parameter of the highest RTP session incremented by 1. Initial buffering lasts until one of the following conditions is fulfilled: o There are N or more VCL NAL units in the de-session-multiplexing buffer. o If sprop-semul-max-don-diff of the highest SVC RTP session is present, don_diff(m,n) is greater than the value of sprop-semul- max-don-diff of the highest RTP session, in which n corresponds to the NAL unit having the greatest value of AbsDON among the received NAL units and m corresponds to the NAL unit having the smallest value of AbsDON among the received NAL units. Wenger, et al Expires November 15, 2008 [Page 38] Internet-Draft RTP Payload Format for SVC Video May 2008 o Initial buffering has lasted for the duration equal to or greater than the value of the OPTIONAL sprop-desemul-init-buf-time media type parameter of the highest SVC RTP session. The NAL units to be removed from the de-session-multiplexing buffer are determined as follows: o If the de-session-multiplexing buffer contains at least N VCL NAL units, NAL units are removed from the de-session-multiplexing buffer and passed to the decoder in the order specified below until the buffer contains N-1 VCL NAL units. o If sprop-semul-max-don-diff of the highest SVC RTP session is present, all NAL units m for which don_diff(m,n) is greater than sprop-max-don-diff of the highest RTP session are removed from the de-session-multiplexing buffer and passed to the decoder in the order specified below. Herein, n corresponds to the NAL unit having the greatest value of AbsDON among the NAL units in the de- session-multiplexing buffer. The order in which NAL units are passed to the decoder is specified as follows: o Let PDON be a variable that is initialized to 0 at the beginning of the RTP sessions. o For each NAL unit associated with a value of CS-DON, a CS-DON distance is calculated as follows. If the value of CS-DON of the NAL unit is larger than the value of PDON, the CS-DON distance is equal to CS-DON - PDON. Otherwise, the CS-DON distance is equal to 65535 - PDON + CS-DON + 1. o NAL units are delivered to the decoder in ascending order of CS- DON distance. If several NAL units share the same value of CS-DON distance, they can be passed to the decoder in any order. o When a desired number of NAL units have been passed to the decoder, the value of PDON is set to the value of CS-DON for the last NAL unit passed to the decoder. 9. Payload Format Parameters This section specifies the parameters that MAY be used to select optional features of the payload format and certain features of the bitstream. The parameters are specified here as part of the media type registration for the SVC codec. A mapping of the parameters into the Session Description Protocol (SDP) [RFC4566] is also Wenger, et al Expires November 15, 2008 [Page 39] Internet-Draft RTP Payload Format for SVC Video May 2008 provided for applications that use SDP. Equivalent parameters could be defined elsewhere for use with control protocols that do not use SDP. Some parameters provide a receiver with the properties of the stream that will be sent. The names of all these parameters start with "sprop" for stream properties. Some of these "sprop" parameters are limited by other payload or codec configuration parameters. For example, the sprop-parameter-sets parameter is constrained by the profile-level-id parameter. The media sender selects all "sprop" parameters rather than the receiver. This uncommon characteristic of the "sprop" parameters may not be compatible with some signaling protocol concepts, in which case the use of these parameters SHOULD be avoided. 9.1. Media Type Registration The media subtype for the SVC codec is allocated from the IETF tree. The receiver MUST ignore any unspecified parameter. Informative note: Requiring that the receiver ignores unspecified parameters allows for backward compatibility of future extensions. For example, if a future specification that is backward compatible to this specification specifies some new parameters, then a receiver according to this specification is capable of receiving data per the new payload but ignoring those parameters newly specified in the new payload specification. This provision is also present in RFC 3984. Media Type name: video Media subtype name: H264-SVC or H264 The media subtype "H264" MUST be used for RTP streams using RFC 3984, i.e. not using any of the new features introduced by this specification compared to RFC 3984. [Edt. Note: The new features are to be listed herein.] For RTP streams using any of the new features introduced by this specification compared to RFC 3984, the media subtype "H264-SVC" SHOULD be used, and the media subtype "H264" MAY be used. Use of the media subtype "H264" for RTP streams using the new features allows for RFC 3984 receivers to negotiate and receive H.264/AVC or SVC streams packetized according to this specification, but to ignore media parameters and NAL unit types it does not recognize. Required parameters: none Wenger, et al Expires November 15, 2008 [Page 40] Internet-Draft RTP Payload Format for SVC Video May 2008 OPTIONAL parameters: profile-level-id: A base16 [RFC3548] (hexadecimal) representation of the following three bytes in the sequence parameter set NAL unit specified in [SVC]: 1) profile_idc, 2) a byte herein referred to as profile-iop, composed of the values of constraint_set0_flag, constraint_set1_flag, constraint_set2_flag, constraint_set3_flag, and reserved_zero_4bits in bit-significance order, starting from the most significant bit, and 3) level_idc. Note that reserved_zero_4bits is required to be equal to 0 in [SVC], but other values for it may be specified in the future by ITU-T or ISO/IEC. If the profile-level-id parameter is used to indicate properties of a NAL unit stream, it indicates the profile and level that a decoder has to support in order to comply with [SVC] when it decodes the NAL unit stream. The profile-iop byte indicates whether the NAL unit stream also obeys all the constraints as specified in subsection G.7.4.2.1.1 of [SVC]. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, and all NAL units conveyed in other RTP sessions, if present, the current RTP session depends on. The current RTP session MAY depend on other RTP sessions when a scalable bitstream is transported with more than one RTP session and the current session is not an independent RTP session. If the profile-level-id parameter is used for capability exchange or session setup procedure, it indicates the profile that the codec supports and the highest level supported for the signaled profile. The profile-iop byte indicates whether the codec has additional limitations whereby only the common subset of the algorithmic features and limitations signaled with the profile-iop byte is supported by the codec. For example, if a codec supports only the common subset of the coding tools of the Baseline profile and the Main profile at level 2.1 and below, the profile-level-id becomes 42E015, in which 42 stands for the Baseline profile, E0 indicates that only the common subset for all profiles is supported, and 15 indicates level 2.1. Informative note: Capability exchange and session setup procedures should provide means to list the capabilities for each supported codec profile separately. For example, Wenger, et al Expires November 15, 2008 [Page 41] Internet-Draft RTP Payload Format for SVC Video May 2008 the one-of-N codec selection procedure of the SDP Offer/Answer model can be used (section 10.2 of [RFC4566]). If no profile-level-id is present, the Baseline Profile without additional constraints at Level 1 MUST be implied. max-mbps, max-fs, max-cpb, max-dpb, and max-br: The common property of these parameters is as specified in RFC 3984. max-mbps: This parameter is as specified in RFC 3984. max-fs: This parameter is as specified in RFC 3984. max-cpb: The value of max-cpb is an integer indicating the maximum coded picture buffer size in units of 1000 bits for the VCL HRD parameters (see A.3.1 item i or G.10.2.2 item g of [SVC]) and in units of 1200 bits for the NAL HRD parameters (see A.3.1 item j or G.10.2.2 item h of [SVC]). The max-cpb parameter signals that the receiver has more memory than the minimum amount of coded picture buffer memory required by the signaled level conveyed in the value of the profile-level-id parameter. When max-cpb is signaled, the receiver MUST be able to decode NAL unit streams that conform to the signaled level, with the exception that the MaxCPB value in Table A-1 of [SVC] for the signaled level is replaced with the value of max-cpb. The value of max-cpb MUST be greater than or equal to the value of MaxCPB for the level given in Table A-1 of [SVC]. Senders MAY use this knowledge to construct coded video streams with greater variation of bit rate than can be achieved with the MaxCPB value in Table A-1 of [SVC]. Informative note: The coded picture buffer is used in the hypothetical reference decoder (Annex C) of [SVC]. The use of the hypothetical reference decoder is recommended in SVC encoders to verify that the produced bitstream conforms to the standard and to control the output bitrate. Thus, the coded picture buffer is conceptually independent of any other potential buffers in the receiver, including de- interleaving and de-jitter buffers. The coded picture buffer need not be implemented in decoders as specified in Annex C of [SVC], but rather standard-compliant decoders can have any buffering arrangements provided that they can decode standard-compliant bitstreams. Thus, in practice, the input buffer for video decoder can be integrated with de-interleaving and de-jitter buffers of the receiver. Wenger, et al Expires November 15, 2008 [Page 42] Internet-Draft RTP Payload Format for SVC Video May 2008 max-dpb: This parameter is as specified in RFC 3984. max-br: The value of max-br is an integer indicating the maximum video bit rate in units of 1000 bits per second for the VCL HRD parameters (see A.3.1 item i or G.10.2.2 item g of [SVC]) and in units of 1200 bits per second for the NAL HRD parameters (see A.3.1 item j or G.10.2.2 item h of [SVC]). The max-br parameter signals that the video decoder of the receiver is capable of decoding video at a higher bit rate than is required by the signaled level conveyed in the value of the profile-level-id parameter. When max-br is signaled, the video codec of the receiver MUST be able to decode NAL unit streams that conform to the signaled level, conveyed in the profile-level-id parameter, with the following exceptions in the limits specified by the level: o The value of max-br replaces the MaxBR value of the signaled level (in Table A-1 of [SVC]). o When the max-cpb parameter is not present, the result of the following formula replaces the value of MaxCPB in Table A-1 of [SVC]: (MaxCPB of the signaled level) * max-br / (MaxBR of the signaled level). For example, if a receiver signals capability for Level 1.2 with max-br equal to 1550, this indicates a maximum video bitrate of 1550 kbits/sec for VCL HRD parameters, a maximum video bitrate of 1860 kbits/sec for NAL HRD parameters, and a CPB size of 4036458 bits (1550000 / 384000 * 1000 * 1000). The value of max-br MUST be greater than or equal to the value MaxBR for the signaled level given in Table A-1 of [SVC]. Senders MAY use this knowledge to send higher bitrate video as allowed in the level definition of SVC, to achieve improved video quality. Informative note: This parameter was added primarily to complement a similar codepoint in the ITU-T Recommendation H.245, so as to facilitate signaling gateway designs. No assumption can be made from the value of this parameter that the network is capable of handling such bit rates at any given time. In particular, no conclusion can be drawn Wenger, et al Expires November 15, 2008 [Page 43] Internet-Draft RTP Payload Format for SVC Video May 2008 that the signaled bit rate is possible under congestion control constraints. redundant-pic-cap: This parameter is as specified in RFC 3984. sprop-parameter-sets: This parameter MAY be used to convey any sequence parameter set, subset sequence parameter set and picture parameter set NAL units (herein referred to as the initial parameter set NAL units) that MUST be placed in the NAL unit stream to precede any other NAL units in decoding order by the receiver. The parameter MUST NOT be used to indicate codec capability in any capability exchange procedure. The value of the parameter is the base64 [RFC3548] representation of the initial parameter set NAL units as specified in sections 7.3.2.1, 7.3.2.2 and G.7.3.2.1 of [SVC]. The parameter sets are conveyed in decoding order, and no framing of the parameter set NAL units takes place. A comma is used to separate any pair of parameter sets in the list. Note that the number of bytes in a parameter set NAL unit is typically less than 10, but a picture parameter set NAL unit can contain several hundreds of bytes. Informative note: When several payload types are offered in the SDP Offer/Answer model, each with its own sprop- parameter-sets parameter, then the receiver cannot assume that those parameter sets do not use conflicting storage locations (i.e., identical values of parameter set identifiers). Therefore, a receiver should double-buffer all sprop-parameter-sets and make them available to the decoder instance that decodes a certain payload type. parameter-add: This parameter is as specified in RFC 3984. packetization-mode: This parameter is as specified in RFC 3984. sprop-interleaving-depth: This parameter is as specified in RFC 3984. sprop-deint-buf-req: This parameter is as specified in RFC 3984. deint-buf-cap: This parameter is as specified in RFC 3984. Wenger, et al Expires November 15, 2008 [Page 44] Internet-Draft RTP Payload Format for SVC Video May 2008 sprop-init-buf-time: This parameter is as specified in RFC 3984. sprop-max-don-diff: This parameter is as specified in RFC 3984. max-rcmd-nalu-size: This parameter is as specified in RFC 3984. session-multiplexing-packetization-mode: This parameter signals the properties of a NAL unit stream carried in more than one RTP session using session multiplexing or the capabilities of a receiver implementation. When the value of session-multiplexing-packetization-mode is equal to 0, the NI-T mode MUST be used. When the value of session-multiplexing-packetization-mode is equal to 1, the NI- C mode MUST be used. When the value of session-multiplexing- packetization-mode is equal to 2 or session-multiplexing- packetization-mode is not present, the NI-TC mode MUST be used. When the value of session-multiplexing-packetization- mode is equal to 3, the I-C mode MUST be used. The value of session-multiplexing-packetization-mode MUST be an integer in the range of 0 to 3, inclusive. sprop-session-multiplexing-depth: This parameter MUST NOT be present when the value of session- multiplexing-packetization-mode is equal to 0. This parameter MUST be present when the value of session-multiplexing- packetization-mode is larger than 0 or session-multiplexing- packetization-mode is not present. This parameter signals the properties of a NAL unit stream carried in the current RTP session and the RTP sessions the current RTP session depends on. It is guaranteed that receivers can reconstruct NAL unit decoding order as specified in Subsection 8.1.2. of this memo when the de-session- multiplexing buffer size is at least the value of sprop- session-multiplexing-depth + 1 in terms of VCL NAL units. The value of sprop-session-multiplexing-depth MUST be an integer in the range of 0 to 32767, inclusive. sprop-desemul-buf-req: This parameter MUST NOT be present when the value of session- multiplexing-packetization-mode is equal to 0. It MUST be present when session-multiplexing-packetization-mode is not Wenger, et al Expires November 15, 2008 [Page 45] Internet-Draft RTP Payload Format for SVC Video May 2008 present or the value of session-multiplexing-packetization- mode is larger than 0. sprop-desemul-buf-req signals the required size of the de- session-multiplexing buffer for the NAL unit stream carried in the current RTP session and the RTP sessions the current RTP session depends on. It is guaranteed that receivers can recover the decoding order of the received NAL units from the current RTP session and the RTP sessions the current RTP session depends on as specified in section 8.1.2. , when the de-session-multiplexing buffer size is at least the value of sprop-desemul-buf-req in terms of bytes. The value of sprop-desemul-buf-req MUST be an integer in the range of 0 to 4294967295, inclusive. desemul-buf-cap: This parameter signals the capabilities of a receiver implementation and indicates the amount of de-session- multiplexing buffer space in units of bytes that the receiver has available for recovering the NAL unit decoding order as specified in section 8.1.2. . A receiver is able to handle any NAL unit stream for which the value of the sprop-desemul- buf-req parameter is smaller than or equal to this parameter. If the parameter is not present, then a value of 0 MUST be used for desemul-buf-cap. The value of desemul-buf-cap MUST be an integer in the range of 0 to 4294967295, inclusive. sprop-desemul-init-buf-time: This parameter MAY be used to signal the properties of a NAL unit stream carried in the current RTP session and the RTP sessions the current RTP session depends on. The parameter MUST NOT be present if session-multiplexing-packetization-mode is not present or the value of session-multiplexing- packetization-mode is larger than 0. The parameter signals the initial buffering time that a receiver MUST wait before starting to recover the NAL unit decoding order as specified in Subsection 8.1.2. of this memo. The parameter is coded as a non-negative base10 integer representation in clock ticks of a 90-kHz clock. If the parameter is not present, then no initial buffering time value is defined. Otherwise the value of sprop-desemul-init-buf- Wenger, et al Expires November 15, 2008 [Page 46] Internet-Draft RTP Payload Format for SVC Video May 2008 time MUST be an integer in the range of 0 to 4294967295, inclusive. sprop-semul-max-don-diff: This parameter MAY be used to signal the properties of a NAL unit stream carried in the current RTP session and the RTP sessions the current RTP session depends on. It MUST NOT be used to signal transmitter or receiver or codec capabilities. The parameter MUST NOT be present if the value of session- multiplexing-packetization-mode is equal to 0. sprop-semul- max-don-diff is an integer in the range of 0 to 32767, inclusive. If sprop-semul-max-don-diff is not present, the value of the parameter is unspecified. sprop-semul-max-don- diff is calculated same as sprop-max-don-diff as specified in RFC 3984, with decoding order number being replaced by cross- session decoding order number. sprop-prebuf-size: This parameter MAY be present when the current RTP session depends on any other RTP session. This parameter MUST NOT be present when session-multiplexing-packetization-mode is not present or the value of session-multiplexing-packetization- mode is larger than 0. sprop-prebuf-size MAY signal the required size of the receiver buffer for the NAL unit stream per RTP session. This parameter may be useful to compensate the impact of inter-RTP session jitter, when the receiver buffer size is at least the value of sprop-prebuf-size in terms of bytes. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session. The value of sprop-prebuf-size MUST be an integer in the range of 0 to 4294967295, inclusive. Informative note: sprop-prebuf-size indicates the required size of the prebuffering receiver buffer only. When network jitter can occur, an appropriately sized jitter buffer has to be provisioned for as well. When a scalable bitstream is conveyed in more than one RTP session, and the sessions initiates at different time, the session initiation variation has also to be compensated by an appropriately sized buffer. sprop-prebuf-time: This parameter MAY be used to signal the properties of a NAL unit stream within a session multiplexing. Herein the NAL unit stream refers to the one consisting of all NAL units Wenger, et al Expires November 15, 2008 [Page 47] Internet-Draft RTP Payload Format for SVC Video May 2008 conveyed in the current RTP session. This parameter MUST NOT be present when session-multiplexing-packetization-mode is not present or the value of session-multiplexing-packetization- mode is larger than 0. The parameter signals the initial buffering time used for a receiver before starting to recover the NAL unit decoding order for more than one RTP session. The parameter is the maximum value of (transmission time of a NAL unit - decoding time of the NAL unit), assuming reliable and instantaneous transmission, the same timeline for transmission and decoding, and that decoding starts when the first packet arrives. The parameter is coded as a non-negative base10 integer representation in clock ticks of a 90-kHz clock. If the parameter is not present, then no initial buffering time value is defined. Otherwise the value of sprop-prebuf-time MUST be an integer in the range of 0 to 4294967295, inclusive. In addition to the signaled sprop-prebuf-time, receivers SHOULD take into account the transmission delay jitter buffering, including buffering for the delay jitter caused by mixers, translators, gateways, proxies, traffic-shapers, and other network elements. Yet another aspect receivers SHOULD take into account is the session initiation variation when a scalable bitstream is conveyed in more than one session, including buffering the variation. [Ed.Note(YkW): Need to discuss how inter-RTP session jitter should be handled in general, and how it works by using sprop- prebuf-size and sprop-prebuf-time.] sprop-scalability-info: This parameter MAY be used to convey the NAL unit containing the scalability information SEI message as specified in Annex G of [SVC]. This parameter MAY be used to signal the contained Layers of an SVC bitstream. The parameter MUST NOT be used to indicate codec capability in any capability exchange procedure. The value of the parameter is the base64 representation of the NAL unit containing the scalability information SEI message. If present, the NAL unit MUST contain only a scalability information SEI message. This parameter MAY be used in an offering or declarative SDP message to indicate what Layers can be provided. A receiver MAY indicate its choice of one Layer using the optional media type parameter scalable-layer-id. Wenger, et al Expires November 15, 2008 [Page 48] Internet-Draft RTP Payload Format for SVC Video May 2008 sprop-layer-range: This parameter MAY be used to signal two sets of the layer identification values of the lowest and highest operation points conveyed in the RTP session. Each set is a base16 representation of a three-character value, with the first character representing DID, the second character representing QID, and the third character representing TID. The two sets are comma separated. Let DIDl and DIDh be the least DID value and the greatest DID value, respectively, among all the NAL units conveyed in the RTP session. Let QIDl and TIDl be the least QID value and the least TID value, respectively, among all the NAL units that are conveyed in the RTP session and that have DID equal to DIDl. Let QIDh and TIDh be the greatest QID value and the great TID value, respectively, among all the NAL units that are conveyed in the RTP session and that have DID equal to DIDh. The first set indicates the DID, QID and TID values of the lowest operation point, for which the DID, QID and TID values are equal to DIDl, QIDl, and TIDl, respectively. The second set indicates the DID, QID and TID values of the highest operation point, for which the DID, QID and TID values are equal to DIDh, QIDh, and TIDh, respectively. scalable-layer-id: This parameter MAY be used to signal a receiver's choice of the offers or declared operation points or layers using sprop- scalability-info. The value of scalable-layer-id is a base16 representation of the layer_id[ i ] syntax element in the scalability information SEI message as specified in [SVC]. [Edt. Note (TS): That is, a SDP capable receiver/middle-box must decode the sprop-scalabiltiy-info syntax, which is not specified in this memo, to select a scalable-layer-id. This is currently not addressed in the offer answer section!] sprop-spatial-resolution: [Edt. Note: I know that framerate and bitrate SDP parameters are already available, but failed to find a spatial resolution SDP parameter. It would be good if this is already defined. Otherwise, it would be better to be defined somewhere else because it is a generic parameter.] This parameter MAY be used to indicate the property of a stream or the capability of a receiver or sender implementation. The value is a base16 of the width and height of the spatial resolution, in pixels, separated by a comma. Wenger, et al Expires November 15, 2008 [Page 49] Internet-Draft RTP Payload Format for SVC Video May 2008 [Edt. Note (TS): Shouldn't this be a generic SDP parameter?] Encoding considerations: This type is only defined for transfer via RTP (RFC 3550). Security considerations: See section 10. of RFC XXXX. Public specification: Please refer to RFC XXXX and its section 14. . Additional information: None File extensions: none Macintosh file type code: none Object identifier or OID: none Person & email address to contact for further information: Intended usage: COMMON Author: Change controller: IETF Audio/Video Transport working group delegated from the IESG. 9.2. SDP Parameters [Edt. Note: For agreeing on a Layer or OP in unicast, an SDP can contain multiple m lines with bitrate, framerate and spatial resolution parameters available, in addition to sprop-scalability- info. The receive can select one of the m lines, or, for operation points that are not included in the m lines, one of the "scalable layers" specified by sprop-scalabiltiy-info using scalable-layer-id. For layered multicast, then the grouping signaling in I-D.ietf- mmusic-decoding-dependency is needed. The above would conveniently support also the normal ROI use cases (with a few ROIs each indicated as a "scalable layer") but not the interactive ROI use cases. The quality layer using priority_id use cases are not supported either. That would need one more optional media type parameter, to identify a quality layer. The lightweight Wenger, et al Expires November 15, 2008 [Page 50] Internet-Draft RTP Payload Format for SVC Video May 2008 transcoding use cases should be supported well by using (multiple) normal AVC SDP offering messages.] 9.2.1. Mapping of Payload Type Parameters to SDP The media type video/H264-SVC string is mapped to fields in the Session Description Protocol (SDP) as follows: o The media name in the "m=" line of SDP MUST be video. o The encoding name in the "a=rtpmap" line of SDP MUST be H264-SVC (the media subtype). o The clock rate in the "a=rtpmap" line MUST be 90000. o The OPTIONAL parameters "profile-level-id", "max-mbps", "max-fs", "max-cpb", "max-dpb", "max-br", "redundant-pic-cap", "sprop- parameter-sets", "parameter-add", "packetization-mode", "sprop- interleaving-depth", "deint-buf-cap", "sprop-deint-buf-req", "sprop-init-buf-time", "sprop-max-don-diff", "max-rcmd-nalu-size", "session-multiplexing-packetization-mode", "sprop-session- multiplexing-depth", "sprop-desemul-buf-req", "desemul-buf-cap", "sprop-desemul-init-buf-time", "sprop-semul-max-don-diff", "sprop- prebuf-size", "sprop-prebuf-time", "sprop-layer-range", "sprop- scalability-info", "scalable-layer-id", and "sprop-spatial- resolution", when present, MUST be included in the "a=fmtp" line of SDP. These parameters are expressed as a media type string, in the form of a semicolon separated list of parameter=value pairs. 9.2.2. Usage with the SDP Offer/Answer Model When H.264 or SVC is offered over RTP using SDP in an Offer/Answer model [RFC3264] for negotiation for unicast usage, the following limitations and rules apply: o The parameters identifying a media format configuration for H.264 or SVC are "profile-level-id", "packetization-mode", and, if required by "packetization-mode", "sprop-deint-buf-req". These three parameters MUST be used symmetrically; i.e., the answerer MUST either maintain all configuration parameters or remove the media format (payload type) completely, if one or more of the parameter values are not supported. Informative note: The requirement for symmetric use applies only for the above three parameters and not for the other stream properties and capability parameters. Wenger, et al Expires November 15, 2008 [Page 51] Internet-Draft RTP Payload Format for SVC Video May 2008 To simplify handling and matching of these configurations, the same RTP payload type number used in the offer SHOULD also be used in the answer, as specified in [RFC3264]. An answer MUST NOT contain a payload type number used in the offer unless the configuration ("profile-level-id", "packetization-mode", and, if present, "sprop-deint-buf-req") is the same as in the offer. Informative note: An offerer, when receiving the answer, has to compare payload types not declared in the offer based on media type (i.e., video/H264-SVC) and the above three parameters with any payload types it has already declared, in order to determine whether the configuration in question is new or equivalent to a configuration already offered. An answerer MAY select from the layers offered in the "sprop- scalability-information" parameter by including "scalable-layer- id" or "sprop-layer-range" in the answer.[Edt. Note: do we need to additionally define behavior with snd/rcvonly parameter?] o The parameters "sprop-parameter-sets"