[FFmpeg-devel] [PATCH] avformat/mpegts: unset DTS/PTS for subtitle PES packets if PCR not available

[Michael Niedermayer]

On Sat, Dec 15, 2018 at 08:50:41PM +0200, Jan Ekström wrote:
> Fixes issues when a subtitle packet is received before PCR for the
> program has been received, leading to wildly jumping timestamps
> on the lavf client side as well as in the re-ordering logic.
> 
> This usually happens in case of multiplexes where the PCR of a
> program is not taken into account with subtitle tracks' DTS/PTS.
> ---
>  libavformat/mpegts.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
> index edf6b5701d..8f6ee81cda 100644
> --- a/libavformat/mpegts.c
> +++ b/libavformat/mpegts.c
> @@ -1219,6 +1219,7 @@ skip:
>                          || pes->st->codecpar->codec_id == AV_CODEC_ID_DVB_SUBTITLE)
>                      ) {
>                      AVProgram *p = NULL;
> +                    int pcr_found = 0;
>                      while ((p = av_find_program_from_stream(pes->stream, p, pes->st->index))) {
>                          if (p->pcr_pid != -1 && p->discard != AVDISCARD_ALL) {
>                              MpegTSFilter *f = pes->ts->pids[p->pcr_pid];
> @@ -1242,6 +1243,7 @@ skip:
>                                      // and the pcr error to this packet should be no more than 100 ms.
>                                      // TODO: we should interpolate the PCR, not just use the last one
>                                      int64_t pcr = f->last_pcr / 300;
> +                                    pcr_found = 1;
>                                      pes->st->pts_wrap_reference = st->pts_wrap_reference;
>                                      pes->st->pts_wrap_behavior = st->pts_wrap_behavior;
>                                      if (pes->dts == AV_NOPTS_VALUE || pes->dts < pcr) {
> @@ -1258,6 +1260,15 @@ skip:
>                              }
>                          }
>                      }
> +
> +                    if (!pcr_found) {
> +                        av_log(pes->stream, AV_LOG_VERBOSE,
> +                               "Forcing DTS/PTS to be unset for a "
> +                               "non-trustworthy PES packet for PID %d as "
> +                               "PCR hasn't been received yet.\n",
> +                               pes->pid);
> +                        pes->dts = pes->pts = AV_NOPTS_VALUE;
> +                    }
>                  }
>              }
>              break;

Assuming i understand the intend correctly ...
could the packet be put in a buffer and once a PCR has been encountered be
returned based on that?
This seems better as no timestamp would be lost

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

"I am not trying to be anyone's saviour, I'm trying to think about the
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