merge_pmt_versions not working properly for transportstream with multiple streams having same stream_identifier

[deeptho]

Summary of the bug:

Some transport streams contain multiple audio streams with the
the same stream_identifier. In this case, when the merge_pmt_versions
option is activated, ffmpeg gets confused.

How to reproduce:

Compare

ffplay -ast 0 00_20201123_230057.ts

  Stream #0:0[0x1b6]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1c1](ita): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 448 kb/s
    Stream #0:2[0x1c2](eng): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, fltp, 128 kb/s
    Stream #0:3[0x24c](ita,ita,eng): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006), 492x250
    Stream #0:4[0x28a](Oth): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, mono, fltp, 64 kb/s
    Stream #0:5[0xbb9]: Unknown: none ([11][0][0][0] / 0x000B)
    Stream #0:6[0xbba]: Unknown: none ([11][0][0][0] / 0x000B)
    Stream #0:7[0x7d1]: Unknown: none ([5][0][0][0] / 0x0005)
    Stream #0:8[0x7d2]: Unknown: none ([5][0][0][0] / 0x0005)
    Stream #0:9[0xc1d]: Unknown: none ([12][0][0][0] / 0x000C)

to

ffplay -merge_pmt_versions 1 -ast 0 00_20201123_230057.ts

   Stream #0:0[0x1b6]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1c1](ita): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 448 kb/s
    Stream #0:2[0x1c2](eng): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, fltp, 96 kb/s
    Stream #0:3[0x24c](ita,ita,eng): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006), 492x250
    Stream #0:4[0xbb9]: Unknown: none ([11][0][0][0] / 0x000B)
    Stream #0:5[0xbba]: Unknown: none ([11][0][0][0] / 0x000B)
    Stream #0:6[0x7d1]: Unknown: none ([5][0][0][0] / 0x0005)
    Stream #0:7[0x7d2]: Unknown: none ([5][0][0][0] / 0x0005)
    Stream #0:8[0xc1d]: Unknown: none ([12][0][0][0] / 0x000C)

The second mp2 stream is missing.

Note that this test stream does not
have pmt changes. The net effect is that in my own viewer
that I am developing the stream fails to play back properly.
I have not been able to create a simple ffplay command that
actually shows a failing playback,

Still an inspection of the source shows the problem:
when the very first pmt is loaded,
"find_matching_stream" is called
with the following audio streams:

pid 450 (eng), stream_identifier=2
pid 650 (Oth), stream_identifier=2
...

The code then decides that 650 replaces 450, which is
of course incorrect.

[deeptho]

parsed version of the pmt (obtained with dvbsnoop)

[Carl Eugen Hoyos]

Please provide the input file.

[Aman]

Yes, please share a small sample file with such a PMT

[Marton Balint]

Also please try alternative patch here:

​http://ffmpeg.org/pipermail/ffmpeg-devel/2020-November/272915.html

[deeptho]

The alternative patch does not appear to work. With the same ffplay command,
I get:

ffplay -merge_pmt_versions 1 -ast 0 00_20201123_230057.ts

Stream #0:0[0x1b6]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
Stream #0:1[0x1c1](ita): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 448 kb/s
Stream #0:2[0x1c2](eng): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, fltp, 96 kb/s
Stream #0:3[0x24c](ita,ita,eng): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006)
Stream #0:4[0xbb9]: Unknown: none ([11][0][0][0] / 0x000B)

So the second mp2 stream is still not found

[deeptho]

Replying to tmm1:

Yes, please share a small sample file with such a PMT

I replied to that mailing list but the email bounced.

I have uploaded a sample on wetransfer.

This is a partial mpeg transport stream. It contain PAT, PMT and all streams related
to the specific program.

​https://we.tl/t-F06CV0xo66

[Marton Balint]

New patch attached here, please comment.

[deeptho]

With the new patch:

ffplay -merge_pmt_versions 1 -ast 0 00_20201123_230057.ts

  Stream #0:0[0x1b6]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1c1](ita): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 448 kb/s
    Stream #0:2[0x1c2](eng): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, fltp, 128 kb/s
    Stream #0:3[0x24c](ita,ita,eng): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006)
    Stream #0:4[0x28a](Oth): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, mono, fltp, 64 kb/s

So this looks good.

[Marton Balint]

In the end this got fixed differently: e57879ec18edab5827268a498577cece82d56811