[FFmpeg-devel] [RFC] Audio normalization

[Clément Bœsch]

On Fri, Feb 22, 2013 at 04:45:56PM +0100, Jan Ehrhardt wrote:
> Clément Bœsch in gmane.comp.video.ffmpeg.devel (Fri, 22 Feb 2013
> 00:22:38 +0100):
> >How to test it:
> >
> >    ./ffplay -f lavfi -i
> >	'amovie=in.mp3,ebur128=video=1:metadata=1[r128-before][a];
> >	[a]volume=metadata=lavfi.r128.I,ebur128=video=1[r128-after][out1];
> >	[r128-before] pad=iw*2 [padded]; [padded][r128-after] overlay=w'
> 
> This one exits immediately in my cross-compiled ffplay.exe, bit that may
> be a problem with the cross-compiling.
> 

The "exits immediately" is what I observe with the other tools under
certain conditions; it's the issue which seems related to the audio
framing I was mentioning. Though, I don't observe it with this
command/filtergraph.

> >Also, there is bug: it seems ffmpeg and ffprobe don't appreciate very much the
> >segmentation through {min,max}_samples in lavfi, and exit very quickly without
> >giving much info (AFAICT it seems the fifo is empty after a first request
> >frame). How to reproduce: after the patchset,
> >    ffmpeg -f lavfi -i 'amovie=in.mp3,ebur128=metadata=1' -f null -
> 
> I am now experimenting with ffmpeg & things like
> 
> -filter_complex
> 	"[0:v]setpts=PTS-STARTPTS[v0]; \
> 	[0:a]asetpts=PTS-STARTPTS,ebur128=metadata=1[a0]; \
> 	[a0]volume=metadata=lavfi.r128.I,ebur128[a1]" \
> 	-map [v0] -map [a1]
> 
> This produces a correct output in ffmpeg, but alas without volume
> correction. But my intuition says something like this should be
> possible. Would that be an idea?
> 

The following seems to work for me:
  ./ffmpeg -i in.mp3 -af ebur128=metadata=1,volume=metadata=lavfi.r128.I -y out.wav

Verified by comparing:
  ./ffplay -f lavfi -i 'amovie=in.mp3,ebur128[out0][out1]'
  ./ffplay -f lavfi -i 'amovie=out.wav,ebur128[out0][out1]'

-- 
Clément B.
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