MPEG-4 Design Team Report

2 Proposals draft-ietf-avt-rtp-mpeg4-02.txt draft-guillemot-genrtp-01.txt draft-jnb-mpeg4av-rtp-00.txt FlexMux packetization

3 Issues Use of MPEG-4 systems vs elementary streams Multiplexing multiple streams Grouping Fragmentation Error protection Timing model Byte alignment

4 Systems vs elementary streams MPEG-4 has a complete system model –some applications need the entire framework –others just desire to use the codecs We accept that we need to generate payload formats for both cases, even though this has the potential for interoperability problems later –compare issues with MPEG-2

5 Systems vs elementary streams MPEG-4 encompasses codecs which may have an existing RTP payload format –This does not preclude the use of MPEG-4 specific packetization in those cases For error resilience, it is desirable to packetize in a media aware manner –This does not imply a choice between systems or elementary streams

6 Multiplexing multiple streams Five multiplexing options were identified –GeRM –FlexMux –“PPP Mux” and CRTP –Don’t multiplex –Don’t multiplex, but compress headers We may need a FlexMux format, but nothing else requires special consideration

7 Grouping within a stream Why group? –to amortize header overhead –to aid error resilience duplicate and group picture headers with each packet group FEC with media data Disagreement over the importance of grouping, and the mechanism to be used

8 Grouping within a stream draft-guillemot-genrtp-01.txt has support for grouping access units (ie: ADUs) and for sub- access units (eg: unequal FEC) –eg: group a repeated picture header with the next frame other proposals perform no additional grouping –assuming anything needed will be done in the encoder need more experimental testing

9 Fragmentation It is necessary to fragment a codec bit-stream in a media aware manner to achieve error resilience We believe that the choice of fragmentation is a matter for the encoder, and that MPEG-4 should be able to fragment accordingly –a payload format should be able to transport oversize fragments, but this need not be efficient

10 Error protection We considered two forms of error protection within the payload across packets

11 Error protection - within payload draft-guillemot-genrtp-01.txt uses unequal FEC within the payload –uses a “typed segment” abstraction for genericity –this abstraction doesn’t exist in MPEG, although the information is available in an ES specific manner other proposals assume the MPEG bitstream is robust enough “as is” need more experimental testing

12 Error protection - across packets May also apply any of the existing error protection mechanisms across packets –parity FEC, for example draft-guillemot-genrtp-01.txt also duplicates these functions as part of its unequal FEC scheme

13 Error Protection Some MPEG-4 elementary streams MUST be reliably delivered –Control streams –Streaming media such as Java class files No conclusion on how we do this - have focused on audio and video to date

14 Timing model MPEG-4 and RTP have different timing models If it is desired to synchronize MPEG-4 data with data using a native RTP packetization we must align the models –capture time vs composition time Believe text in draft-ietf-avt-rtp-mpeg4-02.txt is correct, but needs edits for clarity –see Andrea’s presentation...

15 Byte alignment MPEG-4 systems has the potential to produce not byte aligned bit-streams –audio and video codecs do not –others may? May have to include padding bits to compensate –SL packets include these –mostly affects ES packetization

16 Presentations of drafts...

17 Future directions MPEG-4 codecs can be packetized as any other codec, with standards track payload formats –Adopt draft-jnb-mpeg4av-rtp-00.txt as an AVT work item, for eventual submission on the standards track Multiplexed MPEG-4 media is to be treated in a similar manner to earlier bundled MPEG transport –We will consider a FlexMux payload format, if one is submitted

18 Future directions We do not believe we fully understand the issues involved in the transport of the complete MPEG-4 system over RTP Submit such payload formats for publication as experimental RFCs, whilst we gain implementation experience –draft-ietf-avt-rtp-mpeg4-02.txt –draft-guillemot-genrtp-01.txt