On Sun, 24 Nov 2019, Tomas Härdin wrote:
tor 2019-11-21 klockan 23:35 +0100 skrev Marton Balint:
On Thu, 21 Nov 2019, Tomas Härdin wrote:
> tis 2019-11-19 klockan 19:16 +0000 skrev John Kaplan:
> > Hi Guys,
> >
> > We just did some research on gapless playback across multiple client
> > devices, and could not find support for adding gapless metadata
> > headers in ffmpeg. Our interest is specifically in AAC/MP4, and we
> > ended up shifting to the fdk-aac package, which exposes options for
> > adding moov/edts/elst headers (which are the ones we used) as well as
> > iTunSMPB.
> >
> > So, I wanted to open a discussion with the team on ffmpeg support for
> > gapless metadata.
> > I’m not sure if you guys have discussed before, so here are a few
> > opening questions to get me up to speed…
> >
> >
> > 1. Does ffmpeg support addition of gapless metadata in any form
> > currently, and we missed the doc as to how to specify it?
> > 2. If not, have you discussed previously? If so, what were the
> > results? (I.e. rejected as evil, put on roadmap but in future,
> > currently in development, etc.)
>
> Something very similar to this is being discussed in
> https://trac.ffmpeg.org/ticket/8366
>
> > 3. If support is still in the future, would you be open to me
> > contributing a patch that implements it?
>
> Yes please
>
> I think opening a generic ticket for this would be a good move. Having
> the ability to trim essence would be very useful. Then we could also
> remove that godawful hack in mov.c as well, hopefully. There's more
> than a few formats that need some "warm-up" data or that leave a few
> frames of garbage at the end of the file, like all block transform
> audio codecs
For audio we have AV_PKT_DATA_SKIP_SAMPLES packet side data
This is not enough for sample-level cutting as needed for gapless
playback
Why not? The side data contains the number of samples to be skipped from
the start and at the end of the packet.
for video AV_PKT_FLAG_DISCARD packet flag. What else is needed?
Why is this on the packets? It's not the demuxer's job to decide what
should and should not be cut.
The demuxer only signals this, frames are dropped after they are decoded
in generic libavcodec decode.c.
Regards,
Marton
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