[FFmpeg-devel] [PATCH] Properly store sampling rate for FLAC in mp4

[Ronald S. Bultje]

Hi,

On Wed, Oct 25, 2017 at 5:57 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com>
wrote:

> 2017-10-25 16:52 GMT+02:00 Jean-Yves Avenard <jyavenard at gmail.com>:
> > hi
> >
> > On 26 August 2017 at 12:08, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> >> 2017-08-25 13:25 GMT+02:00 Jean-Yves Avenard <jyavenard at gmail.com>:
> >>
> >>> +            if (track->par->codec_id == AV_CODEC_ID_FLAC) {
> >>
> >> Why does this only apply to flac?
> >>
> >
> > Sorry, I had missed your reply.
> >
> > The specification on how sampling rate is to be stored should it be
> > greater than INT16_MAX is a FLAC in ISOBMFF requirement:
> >
> > https://git.xiph.org/?p=flac.git;a=blob;f=doc/isoflac.txt;h=
> 574df9f54a779fca2e62c726703fc7be199d4c05;hb=refs/heads/master#l165
> >
> > It definitely could be applied to other codecs, but I haven't seen
> > such requirements clearly defined.
> >
> > ISOBMFF only defines that AudioSampleEntryV1 should be used instead,
> > in which case the sampling_rate is a 32 bits integer (ISO 14496-12
> > 12.2.3.2)
>
> Not sure I understand:
> In ticket #6609, I asked if this is a flac-only issue.
> You answered: "The issue can be reproduced with any codec."
>
> So why does your patch only fix the issue for flac?
> Or do I misunderstand?
>

The extension for storing values greater than int16_max is only part of the
isobmff-flac spec, it's not generalized for other audio codecs. Using it
for other audio codecs may have unwanted results, which is why it's
flac-specific.

Do you want a comment in the source code to make this easier to understand
for future developers staring at this code?

Ronald