[FFmpeg-devel] [PATCH 2/3] lavfi/ebur128: add metadata injection.

[Nicolas George]

Le quintidi 25 ventôse, an CCXXI, Jan Ehrhardt a écrit :
> Actually it is useful for volume normalization, in those cases where the
> overall sound level is either too low or too high. I have used Clément's
> first patch set for over 2 weeks now on about 200 videofiles with an
> average duration of 1 hour. It worked exactly as what we expected:
> lowering the sound level of a few recordings and increasing the volume
> of most recordings.

It will work if the volume of the whole movie is approximately constant, but
not at all if you have, for example, a very loud opening and then a quieter
program. Try this for example:

ffmpeg -filter_complex "
flite=text='I am speaking very loudly for a few seconds to confuse
the normalization,
one, two, three, four, five, six, seven, ten,
one, two, three, four, five, six, seven, ten,
one, two, three, four, five, six, seven, ten,
one, two, three, four, five, six, seven, ten
'" -f s16le loud.s16

ffmpeg -filter_complex "
flite=text='Now I am speaking very softly to show that using the integrated
volume for normalization is not a good option', volume=-20dB" -f s16le soft.s16

cat loud.s16 soft.s16 | \
ffmpeg -f s16le -ac 1 -ar 8000 -i - -ar 48000 loudsoft.wav

Of course, no normalization system can deal with quick changes of volume,
but with this example, it will take the integrated loudness more than one
minute to digest the 25 seconds of loud beginning. That is too much.

Regards,

-- 
  Nicolas George
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