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avformat/mpegts: add skip_unknown_pmt option 

Some filtered mpegts streams may erroneously include PMTs for
programs that are not advertised in the PAT. This confuses ffmpeg
and most players because multiple audio/video streams are created
and it is unclear which ones actually contain data.

See for example https://tmm1.s3.amazonaws.com/unknown-pmts.ts

In this sample, the PAT advertises exactly one program. But the
pid it points to for the program's PMT contains PMTs for other
programs as well. This is because the broadcaster decided to
re-use the same pid for multiple program PMTs.

The hardware that filtered the original multi-program stream
into a single-program stream did so by rewriting the PAT to
contain only the program that was requested. But since it just
passed through the PMT pid referenced in the PAT, multiple PMTs
are still present for the other programs.

Before:

    Input #0, mpegts, from 'unknown-pmts.ts':
      Duration: 00:00:10.11, start: 80741.189700, bitrate: 9655 kb/s
      Program 4
        Stream #0:2[0x41]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv, bt709, progressive), 1280x720 [SAR 1:1 DAR 16:9], Closed Captions, 11063 kb/s, 59.94 fps, 59.94 tbr, 90k tbn, 119.88 tbc
        Stream #0:3[0x44](eng): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, 5.1(side), fltp, 384 kb/s
        Stream #0:4[0x45](spa): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 128 kb/s
      No Program
        Stream #0:0[0x31]: Video: mpeg2video ([2][0][0][0] / 0x0002), none(tv), 90k tbr, 90k tbn, 90k tbc
        Stream #0:1[0x34](eng): Audio: ac3 (AC-3 / 0x332D4341), 0 channels, fltp
        Stream #0:5[0x51]: Video: mpeg2video ([2][0][0][0] / 0x0002), none, 90k tbr, 90k tbn
        Stream #0:6[0x54](eng): Audio: ac3 (AC-3 / 0x332D4341), 0 channels

With skip_unknown_pmt=1:

    Input #0, mpegts, from 'unknown-pmts.ts':
      Duration: 00:00:10.11, start: 80741.189700, bitrate: 9655 kb/s
      Program 4
        Stream #0:0[0x41]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv, bt709, progressive), 1280x720 [SAR 1:1 DAR 16:9], Closed Captions, 11063 kb/s, 59.94 fps, 59.94 tbr, 90k tbn, 119.88 tbc
        Stream #0:1[0x44](eng): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, 5.1(side), fltp, 384 kb/s
        Stream #0:2[0x45](spa): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 128 kb/s

Signed-off-by: Aman Gupta <aman@tmm1.net>
This commit is contained in:
Aman Gupta 2018-05-08 12:49:43 -07:00
parent 2940af9389
commit e24d768a76
2 changed files with 8 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
doc/demuxers.texi
View File

@ -538,6 +538,9 @@ This demuxer accepts the following options:
Set size limit for looking up a new synchronization. Default value is
65536.
@item skip_unknown_pmt
Skip PMTs for programs not defined in the PAT. Default value is 0.
@item fix_teletext_pts
Override teletext packet PTS and DTS values with the timestamps calculated
from the PCR of the first program which the teletext stream is part of and is

5
libavformat/mpegts.c
View File

@ -143,6 +143,7 @@ struct MpegTSContext {
int skip_changes;
int skip_clear;
int skip_unknown_pmt;
int scan_all_pmts;
@ -172,6 +173,8 @@ static const AVOption options[] = {
{.i64 = 0}, 0, 0, AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_EXPORT | AV_OPT_FLAG_READONLY },
{"scan_all_pmts", "scan and combine all PMTs", offsetof(MpegTSContext, scan_all_pmts), AV_OPT_TYPE_BOOL,
{.i64 = -1}, -1, 1, AV_OPT_FLAG_DECODING_PARAM },
{"skip_unknown_pmt", "skip PMTs for programs not advertised in the PAT", offsetof(MpegTSContext, skip_unknown_pmt), AV_OPT_TYPE_BOOL,
{.i64 = 0}, 0, 1, AV_OPT_FLAG_DECODING_PARAM },
{"skip_changes", "skip changing / adding streams / programs", offsetof(MpegTSContext, skip_changes), AV_OPT_TYPE_BOOL,
{.i64 = 0}, 0, 1, 0 },
{"skip_clear", "skip clearing programs", offsetof(MpegTSContext, skip_clear), AV_OPT_TYPE_BOOL,
@ -2028,6 +2031,8 @@ static void pmt_cb(MpegTSFilter *filter, const uint8_t *section, int section_len
if (!ts->scan_all_pmts && ts->skip_changes)
return;
if (ts->skip_unknown_pmt && !get_program(ts, h->id))
return;
if (!ts->skip_clear)
clear_program(ts, h->id);