Quoting John Stebbins (2015-11-05 01:34:41)
> On Wed, 2015-11-04 at 20:12 +0200, Martin Storsjö wrote:
> > On Wed, 4 Nov 2015, Luca Barbato wrote:
> >
> > > On 04/11/15 00:29, John Stebbins wrote:
> > > > This feature allows making associations between audio tracks
> > > > that apple players recognize. E.g. when an ac3 track has a
> > > > tref that points to an aac track, devices that don't support
> > > > ac3 will automatically fall back to the aac track.
> > > >
> > > > Apple used to *guess* these associations, but new products
> > > > (AppleTV 4) no longer guess and this association can only
> > > > be made explicitly now using the "fall" tref.
> > > > ---
> > > > libavformat/movenc.c | 18 ++++++++++++++----
> > > > 1 file changed, 14 insertions(+), 4 deletions(-)
> > > >
> > > > Uncrustify
> > > >
> > > > diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> > > > index 572e781..a6a9d09 100644
> > > > --- a/libavformat/movenc.c
> > > > +++ b/libavformat/movenc.c
> > > > @@ -2285,10 +2285,20 @@ static int mov_write_moov_tag(AVIOContext
> > > > *pb, MOVMuxContext *mov,
> > > > mov->tracks[i].tref_id = mov->tracks[mov
> > > > ->chapter_track].track_id;
> > > > }
> > > > for (i = 0; i < mov->nb_streams; i++) {
> > > > - if (mov->tracks[i].tag == MKTAG('r','t','p',' ')) {
> > > > - mov->tracks[i].tref_tag = MKTAG('h','i','n','t');
> > > > - mov->tracks[i].tref_id =
> > > > - mov->tracks[mov->tracks[i].src_track].track_id;
> > > > + MOVTrack *track = &mov->tracks[i];
> > > > + if (track->tag == MKTAG('r','t','p',' ')) {
> > > > + track->tref_tag = MKTAG('h','i','n','t');
> > > > + track->tref_id = mov->tracks[track
> > > > ->src_track].track_id;
> > > > + } else if (track->enc->codec_type == AVMEDIA_TYPE_AUDIO)
> > > > {
> > > > + AVDictionaryEntry *fallback;
> > > > + fallback = av_dict_get(track->st->metadata,
> > > > "fallback", NULL, 0);
> > > > + if (fallback != NULL) {
> > > > + int index = strtol(fallback->value, NULL, 0);
> > > > + if (index >= 0 && index < mov->nb_streams) {
> > > > + track->tref_tag = MKTAG('f','a','l','l');
> > > > + track->tref_id = mov->tracks[index].track_id;
> > > > + }
> > > > + }
> > > > }
> > > > }
> > > >
> > > >
> > >
> > > Martin, if it is ok for you I'd get this in tonight.
> >
> > Hmm, well, metadata is a bit uncomfortable for this, but I don't have
> > a
> > better suggestion either. Anton?
>
> The other option I considered was AVStream side_data. It's a bit more
> work to do it that way, but if you would like that better *shrug*.
I think side data is the proper way to do this. Metadata is intended to
store only information about the content itself, not the technical
details about how it is encoded.
--
Anton Khirnov
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