TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

Sync Layer. The SL-packetized streams provide timing and synchronization information, as well as
fragmentation and random access information. The SL-packetized streams are multiplexed into a
FlexMux stream at the Delivery Layer, which is then passed to the transport protocol stacks such as
RTP/UDP/IP. The resulting IP packets are then transported over the network.
At the receiver side, the video stream is processed in the reversed manner before its
presentation. The received AVOs are decoded and buffered before being composed by the player.
To transmit MPEG-4 stream over the network, it is necessary to adapt this stream to the
network. This is performed by the Application Level Framing (ALF) protocols. ALF protocol
allows the application to get its own control over mechanisms that traditionally fall within the
transport layer e.g., loss detection and recovery. ALF differ from one stream to another. It is
specific to a particular stream format and application. A common ALF used for multimedia
application is the RTP protocol.
There are a number of RTP packetization schemes for MPEG-4 data. Some works presented
in [156], [157], [158], [159] and [160] specify how the MPEG-4 streams should be fragmented and
packetized to be conveyed over IP network. We summery these works as follows:
• MPEG-4 System over RTP (Section 4.2.1.1)
• MPEG-4 System over RTP with Error Protection (Section 4.2.1.2)
• RTP Payload Format for MPEG-4 Audio/Visual Streams (Section 4.2.1.3)
• RTP Payload Format with Reduced SL Header (Section 4.2.1.4)
• RTP Payload Format for MPEG-4 FlexMultiplexed Streams(Section 4.2.1.5)
It is clear that many packetization schemes can be implemented together in one terminal. Each
packetization scheme is basically adapted to a particular media stream. This technique is called
media-aware packetization. For example, a video object plane is fragmented at recoverable subframe
boundaries to avoid any error propagation.
It is likely that several RTP packetization schemes will be needed to suit the different kinds of
media types and encoding. Also, it is clear that the video packetization scheme is not the same as
the audio packetization scheme. Thus, we proposed and new RTP payload scheme for MPEG-4
Video transport over IP and for MPEG-4 audio.
4.2.1 Related Work
4.2.1.1 MPEG-4 System over RTP
This is the generic approach for encapsulating audiovisual data over RTP [161]. MPEG-4 SL-
PDU packets are directly encapsulated into RTP packet without optimization. This approach is
implemented by using the transmission time or the MPEG-4 composition time to initialize the RTP
timestamp field. However, due to the duplication of header information, like sequence numbering
and time stamps, this approach increases the overhead and it is not considered as efficient.
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