[FFmpeg-devel] A few filter questions

Nicolas George george at nsup.org
Thu Jul 17 18:40:00 CEST 2014

Le nonidi 29 messidor, an CCXXII, Clément Bœsch a écrit :
> We add a discussion several time for real time with that filter. If we do
> a 2-pass, that's simply because it's "more efficient". Typically, doing
> some live normalization can be done easily (we had patches for this):
> ebur128 already attaches some metadata to frames, so a following filter
> such as volume could reuse them, something like -filter_complex
> ebur128=metadata=1,volume=metadata.

I believe you are wrong in this paragraph: we do two passes for
normalization because that is the only way of doing it without distortions:
the level of volume adjustment depends on the whole stream.

Normalization can be done in a single pass with distortions, but currently,
no filter is capable of smoothing the measures computed by ebur128 to make
the distortions inaudible. Patch welcome.


  Nicolas George
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