[FFmpeg-devel] Audio normalization with ebur128 and volume, new round

[Clément Bœsch]

This time, the first patch should fix the format negociation for good. I've
tested with the ffplay -af patch (actually the ffplay testing branch), with
previously broken ffmpeg output from the ticket, and various other
combinations.

The second patch is still the metadata injection from ebur128, nothing much
changed.

The last patch is adding a temporary special path for the volnorm metadata in
volume filter. The way it is done will allow adding expression evaluation in a
later patch (by replacing the volnorm argument with a volnorm variable in the
expression). The evalonce field can later be set to the result of
av_eval_is_const(), or maybe to a user specified option (in which case it will
require -af volume=volume=volnorm:evalonce=0 for the normalization case)

I could have taken the volume eval patch from Stefano, but it would have
require too much work for the feature I'm trying to get in for a long while
now. I hope the way I'm proposing to add this feature is a good temporary
trade-off.

Comments very welcome.

Regards,

Note: I'm updating my ebur128 github branch in a few minutes with those 3
patches on top of the ffplay testing branch if anyone wants to do some tests
easily.