MULTIMEDIA SYSTEMS NETWORKING - Tieto- ja …：多媒体系统网络拓子….ppt

* * * * * * * * * * * * * * * * * DMIF defines an interface that provides multimedia applications (and MPEG-4 applications in particular) with the service of an ISO/OSI Session Layer. DMIF uses special (DMIF) URLs for locating services, which can be obtained from local storage, broadcast networks or remote servers. Thus, DMIF allows an application to get content from local storage, broadcast networks or remote servers using a uniform interface. MULTIMEDIA SYSTEMS IREK DEFEE RTP Characteristics RTP can map only one source stream onto RTP session: Multiplexing causes problems; For scale coding, each layer must have its own RTP session and multicast group; Within each RTP session, source can change its data format over time; It allows FEC (Forward Error Correction); Synchronize across different media streams; Provide feedback on the quality of data using packet counts; Identify and keep track of participants; MULTIMEDIA SYSTEMS IREK DEFEE MPEG-4 over RTP/UDP/IP Easiest is to wrap the MPEG-4 SL packet in an RTP packet: High overhead: two full headers; RTCP may not provide enough control for the MPEG-4 stream; Several types of MPEG-4 payloads are being defined by the IETF for different ESs; MULTIMEDIA SYSTEMS IREK DEFEE RTP ES SL payload restrictions RTP packetization is not media aware: No unique scheme can be defined, need a payload definition per payload type (not practical); This may require the definition of new session and scene description mechanisms to deal with all the flows; Common restrictions: RTP timestamp corresponds to composition time stamp (CTS) of MPEG-4 stream; Packets should be sent in decoding order; Streams can be synchronized using RTCP; Map SL stream onto RTP session: SL header is optional; Reduced SL headers does not include: Sequence number (mapped to RTP header); Composition Time Stamp (mapped to RTP header); MULTIMEDIA SYSTEMS IREK DEFEE Streams Media Control in MPEG-4 Multiple S