[FFmpeg-devel] [PATCH v2] avformat/ifv: added support for ifv cctv files

[Reimar Döffinger]

On Sun, May 05, 2019 at 10:05:17PM +0200, Carl Eugen Hoyos wrote:
> Am So., 5. Mai 2019 um 21:59 Uhr schrieb Reimar Döffinger
> <Reimar.Doeffinger at gmx.de>:
> > > +    if (aud_magic == MKTAG('G','R','A','W')) {
> > > +        ifv->is_audio_present = 1;
> > > +    } else if (aud_magic == MKTAG('P','C','M','U')) {
> > > +        ifv->is_audio_present = 0;
> > > +    } else {
> > > +        avpriv_request_sample(s, "Unknown audio codec %x\n", aud_magic);
> > > +    }
> >
> > Why does PCMU mean "no audio"?
>
> We have several files with "PCMU" and several files with "GRAW".
> All files with GRAW contain audio data, none of the files with PCMU
> contain audio data.
> I originally thought that the two bytes at 0x40/0x41 (iirc) show number
> of streams but a test with the proprietary player confirmed that this
> is not correct.
> Another test would be to overwrite GRAW with PCMU to find out if
> audio is still played...

Ok, makes sense.
I think it's good (and good enough) to have a comment that this
is just heuristics/guesswork based on existing samples and
might be quite wrong.