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MPEG2 TS Preamble. Solutions on the table: Problem statement.

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Mpeg2 ts preamble

MPEG2 TS Preamble

Solutions on the table:

Problem statement
Problem statement

  • Demultiplexing and decoding an MPEG2 Transport Stream (MPEG2-TS) requires the knowledge of specific information about the transport stream, which can be spread over different locations throughout the transport stream.

  • The time it takes to retrieve all this information – the MPEG2 TS preamble- for an (RTP) receiver may be long.

  • Idea is to send the “MPEG2 TS preamble” information to a receiver that will shortly start receiving the transport stream, allowing the receiver to start processing/decoding the MPEG2-TS sooner.

Mpeg2 ts preamble rams environment
MPEG2 TS preamble RAMS environment

  • RAP data is sent as retransmission packets in a burst, when an RTP receiver wants rapid acquisition of a SSM RTP (RAMS draft)

  • There are two proposals on how to efficiently send MPEG2 TS preamble data – which is periodically repeated but in general scattered across the MPEG2 TS RTP SSM - alongside with the burst

RAP + Preamble  Transport Stream RAP (TSRAP)

Begen versus xia solution
Begen versus Xia Solution

  • Begen

    • The MPEG2 TS Preamble is wrapped by the RS in dedicated Type-Order-Length-Value (TOLV) elements, encapsulated in RTP packets; e.g. PAT TOLV, PCR TOLV,..

      • The RTP receiver performs a post-processing in order to present this as TS data to the TS demuxer/decoding logic

  • Xia

    • The MPEG2 TS Preamble is sent by the RS as MPEG2 TS/RTP packets (RFC 2250), with TS packets kept unmodified from original Stream

Discussions from mailing list
Discussions from mailing list

  • Begen et. Al. stress that irrespective of the preamble transport method, there must be post-processing done by any receiver design, as existing TS demuxing/decoding logic in most cases will not respond in a desired way to a burst of condensed MPEG2 TS preamble info

    • This was initially contested by Xia et al, but the Xia draft does not preclude such post processing

    • The customised post-processing is not addressed in Begen draft

  • Both solutions do not result in large differences in terms of processing requirements, both at server side and receiver side

  • Some expressed a single solution is preferred, others are OK with both solutions specified by IETF

  • Little specification is required for Xia proposal, but may have slightly more bandwidth overhead compared to Begen draft

    • Not significant when compared to the RAMS burst packet transmissions

  • Discussions on how easy/difficult it is for a MPEG2 TS preamble post-processing stage at the receiver, where starting point is either the Xia format or the Begen format

  • Should the MPEG2 TS preamble also be addressed in a non-RAMS environment?