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

Josh Allmann joshua.allmann at gmail.com
Wed Oct 2 21:10:38 CEST 2013

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.

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