[FFmpeg-devel] [PATCH 2/2] lavfi/volume: support volume normalization through metadata.

[Clément Bœsch]

On Mon, Feb 25, 2013 at 02:14:04AM +0100, Jan Ehrhardt wrote:
> Clément Bœsch in gmane.comp.video.ffmpeg.devel (Fri, 22 Feb 2013
> 00:22:40 +0100):
> >+            new_volume = -23 - loudness;
> >+            //av_log(0,0,"loudness=%f => %f => volume=%f\n", loudness, new_volume, pow(10, new_volume / 20));
> >+            if (loudness > -30)
> >+                set_fixed_volume(vol, pow(10, new_volume / 20));
> 
> Aha, I found the reason why it did not work on my (worst case) sample
> file. The condition 'if (loudness > -30)' prohibited to change the
> volume, because the loudness of the input was -41.6 LUFS:
> 
> [Parsed_ebur128_2 @ 0000000004183a40] Summary:
>   Integrated loudness:
>     I:         -41.6 LUFS
>     Threshold: -51.7 LUFS
> 
>   Loudness range:
>     LRA:         6.0 LU
>     Threshold: -61.7 LUFS
>     LRA low:   -45.0 LUFS
>     LRA high:  -39.0 LUFS
> 
> After removing the condition the volume was raised by something like 8.5
> and produced a file that was right on track with the -23 LUFS as
> recommended by EBU r128:
> 
> [Parsed_ebur128_4 @ 0000000004183f20] Summary:
>   Integrated loudness:
>     I:         -23.0 LUFS
>     Threshold: -33.1 LUFS
> 
>   Loudness range:
>     LRA:         6.0 LU
>     Threshold: -43.1 LUFS
>     LRA low:   -26.4 LUFS
>     LRA high:  -20.4 LUFS
> 
> There was some noise in the background, so maybe the volume change was a
> bit overdone (and should be capped). But it looks promising.
> 

Yeah well the idea of that arbitrary check was to prevent raising the
volume too high (and avoid the noise effect you have). Though, -30 was
likely a very bad value.

-- 
Clément B.
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