[FFmpeg-devel] [RFC] Yet another subtitles open question

[Josh Allmann]

On 2 October 2013 13:03, Michael Niedermayer <michaelni at gmx.at> wrote:
> Hi Josh
>
> On Wed, Oct 02, 2013 at 12:10:38PM -0700, Josh Allmann wrote:
>> On 1 October 2013 11:14, Clément Bœsch <u at pkh.me> wrote:
>> > Hi folks,
>> >
>> > I have definitely better to do, and I still hate subtitles, but we need to
>> > make some changes, and I'm willing to help.
>> >
>> > Shell
>> > -----
>> >
>> > So here it is, I'd like to move on with the API. Currently we use
>> > AVSubtitle (and its AVSubtitleRects) which is defined in lavc. We wanted
>> > at some point to move it to libavutil, eventually with slight changes.
>> > OTOH, the idea of using the AVFrame was disregarded quickly for various
>> > reasons. The thing is, it might have various benefits:
>> >
>> >  - since it doesn't introduce a new struct and its own semantic, it will
>> >    ease a lot its integration with for instance libavfilter, and probably
>> >    allow various code refactoring
>> >
>> >  - AVFrames have a ref counting system: if audio and video are ref
>> >    counted, we expect the subtitles to be as well, otherwise it can become
>> >    a source of pain for users
>> >
>> >  - using AVFrame also suggest the idea that we could embed subtitles data
>> >    within existing AVFrame: think closed captioning. "Freelance" subtitles
>> >    OTOH would just use a empty/zero frame shell. Note that this conflicts
>> >    with the ref counting idea since it can't share the data buffers.
>> >
>> > Opinion on this?
>> >
>>
>> In Libav we're thinking of introducing an opaque field into AVFrame
>> for other purposes, and I'm thinking of leveraging it for
>> subtitle-related things there.
>
> I would suggest that you base your subtitle work on ffmpeg, ubitux,
> nicolas and others have put quite some time into it and if all
> developers interrested in subtitles work together both projects would
> move farther and faster forward in respect to subtitles.
> randonmly rebasing commits from ffmpeg or redoing (and then having to
> retest, redebug, refix, ...) is a really silly thing ...
>

I am inclined to agree. While I can't make the decision alone on how
the subtitle system will look, we have a good opportunity now to
design a system that is satisfactory for both projects.

Josh