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

[Nicolas Gaullier]

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(-)

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2.30.2