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

Nicolas George nicolas.george at normalesup.org
Thu Oct 11 23:21:18 CEST 2012

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

* 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.


  Nicolas George
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