[FFmpeg-devel] [RFC] lavfi: metadata injection

Clément Bœsch ubitux at gmail.com
Thu Oct 11 23:36:37 CEST 2012

On Thu, Oct 11, 2012 at 11:21:18PM +0200, Nicolas George wrote:
> Le nonidi 19 vendémiaire, an CCXXI, Clément Bœsch a écrit :
> >   [PATCH 2/4] lavd: make lavfi device export the metadata up to the
> > 
> >   This one is a proposition of raising information from a lavfi input device up
> >   to AVFrame. It abuses the priv field, but it looks like the simpler way to
> >   me. I had a solution making use of side_data, but it was really too much
> >   code. priv seems mostly unused, and we can move to some other system if
> >   necessary in the future.
> I am not really happy about this, and the perspective of changing the system
> later seems like a source of trouble.
> I can imagine situations where a demuxer would need both the priv field for
> its own private usage and metadata injection. Two examples:
> * The lavfi device could implement direct-rendering instead of copying the
>   frame data, but it would require the priv field to point to the actual
>   AVFilterBuffer.
> * The v4l2 device uses the priv field to manage its DMA buffers, it could
>   need to inject metadata if some device were able to report additional
>   information, such as autofocus info or GPS position.
> The side data is exactly the API intended to extend packets without altering
> the structure. It is a problem if it requires too much code, and indeed some
> well-designed helper functions could help a lot.
> Sorry to be the spoil-sport.

You point out two interesting situations; I believe the proposition in the
other thread should fix these issues :)

Clément B.
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