TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

• Some MPEG-4 elementary streams must be reliably delivered. An example of
theses streams, we can find a control streams BIFS and OD, or streaming media such
as Java class (MPEG-J) files. It is necessary to transport this media in reliable manner.
There is no works that define clearly how to transport this kind of media.
• Addressing the issue of DMIF session management.
• Timing model. MPEG-4 and RTP have different timing models. 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).
Figure 4-9 illustrates the approaches of encapsulating MPEG-4 stream over IP compared to
the ISO MPEG-4 standard approach. To deal with some of the open issues cited later, we have
developed an RTP payload formats for transporting MPEG-4 Audio Visual Object over RTP
protocol called RTP4Mux.
Video
Fragmentation
Compression Layer
Elementary Streams
Sync Layer
Reduced
Sync Layer
Sync Layer
FlexMux
Delivery
Layer
RTP
UDP
IP
RTP
UDP
IP
RTP
UDP
IP
MPEG-4 Standard
Alternative approach
Figure 4-9: Concurrent approaches for encapsulating MPEG-4 stream over the IP networks
4.2.2 An RTP Payload for MPEG-4 Audio / Visual Object
Classical payload format supports a fragmentation mechanism where the full AUs or the
partial AUs passed by the compression layer are fragmented at arbitrary boundaries. This may
result in fragments that are not independently decodable. This kind of fragmentation may be used
in situations when the RTP packets are not allowed to exceed the path-MTU size.
However, this fragmentation is not recommended for error resilience. It is preferable that the
compression layer provides partial AUs, in the form of typed segments, of a size small enough so
that the resulting RTP packet can fit the MTU size.
Consecutive segments (e.g. video frames) of the same type can be packed consecutively in the
same RTP payload. The compression layer should provide partial AUs, of a size small enough so
that the resulting RTP packet can fit the MTU size. Note that passing partial AUs of small size will
also facilitate congestion and rate control based on the real output buffer management. RTP
packets that transport fragments belonging to the same AU will have their RTP timestamp set to
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