[FFmpeg-devel] [PATCH 1/7] avcodec: do not use AVFrame accessor

[Hendrik Leppkes]

On Sat, Apr 22, 2017 at 8:57 PM, Nicolas George <george at nsup.org> wrote:
> Le tridi 3 floréal, an CCXXV, Aaron Levinson a écrit :
>> Then why have the accessors at all if the fields are public?
>
> To ensure ABI compatibility with the fork, which has been dropped.
>

To elaborate on that, the accessors existed primarily for fields which
only exist in FFmpeg, and not in Libav, so that when Libav added a
field, we could add it in the same position as them, and preserve ABI
compatibility to Libav (ie. having all fields in the struct in the
same place).
Due to this practice, any fields Libav didn't have had to be at the
end of the struct, and they would move everytime a new field was added
on Libavs side (which would end up before the FFmpeg-only fields) -
hence accessors to work around the constant ABI changes to these
fields.

But we have decided a while ago that we do no longer want to pretent
to maintain ABI compat (it was never fully functional and basically
untested), and as such there is no need to have them anymore (it was a
bit clumsy to use either  way, as only a minority of fields had them,
so it was easy to use it wrong).

On top of these changes, the accessors should also be deprecated and
then eventually removed (after the typical deprecation period), and
all public fields in the structs accessed directly again.

- Hendrik