The main purpose of discontinuity_indicator flag (which is signaled at ts-packet header) is to make excerpt/segment easliy concatenated or inserted into MPEG-2 Systems stream (TS stream).  Notice that TS stream is commonly comprised from a number of elementary media streams (video and audio). If you wish to concatenate your TS stream to another one you need set discontinuity_indicators flags  at the start (i.e. at the first packet of each elementary stream), otherwise a decoder can derive mistakenly on loss of packets or time async.  

MPEG-2 Systems spec. says:

“A continuity_counter discontinuity is indicated by the use of the discontinuity_indicator in any transport stream packet. When the discontinuity state is true in any transport stream packet of a PID not designated as a PCR_PID, the continuity_counter in that packet may be discontinuous with respect to the previous transport stream packet of the same PID.”

It’s worth mentioning that discontinuity_indicators should be set also in PAT and PMT ts-packet. By the way ATSC A53 allows transmitting of adaptation fields in PAT and PMT only to indicate the continuity counter discontinuity:

“Adaptation headers shall not occur in Transport Stream packets identified by a program_map_PID value for purposes other than for signaling with the discontinuity_indicator
that the version_number (Section 2.4.4.9 of ISO/IEC 13818-1 [3]) may be discontinuous.

Adaptation headers shall not occur in Transport Stream packets identified by PID 0x0000 (the PAT PID) for purposes other than for signaling with the discontinuity_indicator that the
version_number (Section 2.4.4.5 of ISO/IEC 13818-1 [3]) may be discontinuous.”

 

Notes:

  • For safe concatenation or insertion of your excerpt i recommend set discontinuity_indicator at first packets of each elementary stream and at first PAT/PMT

 

  • In addition the discontinuity flag is recommended to be put at the start of each keyframe, even if there is no gap in PCRs. 

 

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