[FFmpeg-devel] [PATCH v3 0/1] avformat/demux: fix accurate probing of durations in mpegts/ps

[Nicolas Gaullier]

>De : Nicolas Gaullier <nicolas.gaullier at cji.paris> 
>Envoyé : mardi 2 avril 2024 23:26
>Objet : [PATCH v3 0/1] avformat/demux: fix accurate probing of durations in mpegts/ps
>
>v3: rebased after ed9363052f4b8b8 applied tonight (add duration_probesize AVOption)
>
>Note: I have no other plan for demux/probing; with these two patches, I can cover my use cases, especially mpegts-concats.
>
>For remembering, previous cover-letters:
>
>v1--------------------
>ff_read_packet() is more lightweight, but it leads to important issues when looking for accurate durations.
>As a side effect, the code looks also simpler with regular av_read_frame() calls.
>1)Updates in the fate tests do exhibit most of the results.
>
>2)See also more directly the case of an audio PES containing many frames:
>>ffprobe tests/data/lavf/lavf.ts -select_streams a -show_entries 
>>stream=duration -of flat
>Before patch:
>  streams.stream.0.duration="0.757556"
>After patch:
>  streams.stream.0.duration="1.018778"
>
>3)Here is an additional (commonplace) sample to demonstrate the benefit for twofields-encoded video:
>>https://0x0.st/HFbm.ts (say h264-50i_mp2.ts)
>
>>ffprobe h264-50i_mp2.ts -show_entries stream=duration -of flat
>Before patch:
>  streams.stream.0.duration="2.060000"
>  streams.stream.1.duration="1.176000"
>After patch:
>  streams.stream.0.duration="2.080000"
>  streams.stream.1.duration="1.200000"
>
>
>v2--------------------
>v1: There was an issue with teletext where resolution is set just once at decoder init (teletext resolution is fixed/hard coded), so it is somewhat fragile: when a demuxer context update occurs, it is lost/overriden by >avcodec_parameters_to_context(sti->avctx, st->codecpar) in read_frame_internal.
>They could have been other scenario besides teletext, I don't know.
>v2: So now at estimate_timings_from_pts, with one or more seeking involved (seeking is detected by the mpegts demuxer and set last_vn=-1, so pmt is forced/updated and results in demuxer context update), it is required to >preserve the info in codecpar at first.
>Thanks to Michael for reporting the issue.
>
>
>Nicolas Gaullier (1):
>  avformat/demux: Fix accurate probing of durations in mpegts/ps
>
> libavformat/demux.c                           |  36 ++--
> tests/ref/fate/concat-demuxer-simple2-lavf-ts | 170 +++++++++---------
> tests/ref/fate/ts-opus-demux                  |   4 +-
> 3 files changed, 100 insertions(+), 110 deletions(-)

Ping for review ?
The patch (https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=11386) still applies on current master.
Thanks.

Nicolas