[FFmpeg-devel] [PATCH] avformat/mpegts: parse large PMTs with multiple tables

[Aman Gupta]

On Tue, Jun 12, 2018 at 3:17 PM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> On Mon, Jun 11, 2018 at 12:43:31AM -0700, Aman Gupta wrote:
> > From: Aman Gupta <aman at tmm1.net>
> >
> > In 9152c1e4955, the mpegts parser was taught how to parse
> > PMT sections which contained multiple tables. That commit
> > fixed parsing of PMT packets from some cable providers,
> > which included a special SCTE table (0xc0) before the
> > standard program map table (0x2).
> >
> > Sometimes, however, the combined 0xc0 and 0x2 tables are
> > larger than a single TS packet (188 bytes). The mpegts parser
> > already attempts to parse sections which span multiple packets,
> > but still assumed that the split section only contained one
> > table.
> >
> > This patch fixes parsing of such a sample[1].
> >
> > Before:
> >
> >     Input #0, mpegts, from 'combined-pmt-tids-split.ts':
> >       Duration: 00:00:01.26, start: 39188.931756, bitrate: 597 kb/s
> >       Program 1
> >       No Program
> >         Stream #0:0[0xeff]: Audio: ac3, 48000 Hz, mono, fltp, 64 kb/s
> >         Stream #0:1[0xefd]: Audio: mp3, 0 channels, fltp
> >         Stream #0:2[0xefe]: Unknown: none
> >
> > After:
> >
> >     Input #0, mpegts, from 'combined-pmt-tids-split.ts':
> >       Duration: 00:00:01.27, start: 39188.931756, bitrate: 589 kb/s
> >       Program 1
> >         Stream #0:0[0xefd]: Video: h264 ([27][0][0][0] / 0x001B), none,
> 59.94 fps, 59.94 tbr, 90k tbn, 180k tbc
> >         Stream #0:1[0xefe](eng): Audio: ac3 ([129][0][0][0] / 0x0081),
> 48000 Hz, stereo, fltp, 384 kb/s
> >         Stream #0:2[0xeff](spa): Audio: ac3 ([129][0][0][0] / 0x0081),
> 48000 Hz, mono, fltp, 64 kb/s
> >         Stream #0:3[0xf00]: Data: scte_35
> >         Stream #0:4[0xf01]: Unknown: none (ETV1 / 0x31565445)
> >         Stream #0:5[0xf02]: Unknown: none (ETV1 / 0x31565445)
> >         Stream #0:6[0xf03]: Unknown: none ([192][0][0][0] / 0x00C0)
> >
> > With the patch, the PMT is parsed correctly so the streams are
> > created in the correct order, are associated with "Program 1",
> > and their codecs are set correctly.
> >
> > [1] https://s3.amazonaws.com/tmm1/combined-pmt-tids-split.ts
> >
> > Signed-off-by: Aman Gupta <aman at tmm1.net>
> > ---
> >  libavformat/mpegts.c | 1 +
> >  1 file changed, 1 insertion(+)
>
> with this change section_h_size becomes almost a local variable
> is that intended ?


Yes that is the intended behavior. Previously the size was cached as an
optimization, but that assumed that there was only one size value per
section (whereas these sections have multiple tables and thus multiple
sizes).

I will follow up with a refactor to turn it into a local variable and
remove the field from the struct.

Aman


>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> The worst form of inequality is to try to make unequal things equal.
> -- Aristotle
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