[FFmpeg-devel] headers for gapless playback

[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, for video 
AV_PKT_FLAG_DISCARD packet flag. What else is needed?

Regards,
Marton