[FFmpeg-devel] On libavfilter: A Summary of Issues

[Clément Bœsch]

On Mon, Feb 18, 2013 at 03:24:58AM +0100, Jan Ehrhardt wrote:
> Clément Bœsch in gmane.comp.video.ffmpeg.devel (Fri, 19 Oct 2012
> 07:49:13 +0200):
> >On Fri, Oct 19, 2012 at 03:06:58AM +0200, Jan Ehrhardt wrote:
> >> Likewise, I am most interested in a port of MEncoder's volnorm filter.
> >> At the moment I'm postprocessing ffmpeg's output with MEncoder, merely
> >> because of the volnorm filter.
> >
> >You'll be able to normalize volume pretty soon©, using the current
> >metadata injection work in progress, ebur128 filter, and the volume
> >filter.
> 
> Quoting this old message...
> 
> Carl Eugen mentioned a discussion you had with kierank on #ffmpeg-devel
> two days ago:
> http://mplayerhq.hu/pipermail/ffmpeg-devel-irc/2013-February/001215.html
> 
> I still like the idea of MEncoder's volnorm filter very much. Even in
> one pass encoding MEncoder adjusts the volume to an acceptable level (in
> my case it mostly gains volume). Would such a thing be possible with
> ebur128 and metadata injection?
> 

AFAICT, yes. We already have metadata injection in lavfi (see
silencedetect or the scene detection in select filter), and so if ebur128
filter was injecting metadata in frames, then a communication would be
possible between ebur128 and volume filter (for example).

The main problem is that you need to adjust ebur128 so it is resizing
frames to windows to something like 100ms (IIRC), which might require some
thinking in the filter. The reason is that a loudness result is associated
for this time frame, so you need to transmit metadata to volume at this
rate.

Another - maybe smarter - solution would be to auto inject a asetnsamples
before a ebur128 filter given various properties of the filtergraph. Or
maybe the ebur128 filter could alter the filtergraph itself (if that's
possible without much hack) to insert the filter before if a "metadata"
mode is requested.

[...]

-- 
Clément B.
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