Bug#797965: bs1770gain somehow "destroys" gapless playback on (at least) lame encoded MP3s

[Christoph Anton Mitterer]

On Sat, 2015-12-19 at 20:59 +0100, Andreas Cadhalpun wrote:
> I might be missing what the problem is, but this command seems to
> work
> just fine with ffmpeg's test sample [1].
> Can you confirm this, or describe more precisely what the problem is?

You need two WAV files, which contain seamlessly playing sound (e.g.
just take any song and split it in the middle).

For lossless formats, there is typically no problem, that these two
play back again seamless (typically called "gapless").

When encoding them to lossy formats however, things get more tricky.
Different format provides for different means of gapless playback (or
none at all).
MP3 has e.g. two widespread ways, one by mean of LAME adding some
special tags, and itunes has something similar.
Opus/Vorbis/AAC, have similar things.

The problem was now, that when such gaplessly encoded files were
processed with bs1770gain, they were no longer gapless afterwards.

Peter thinks, due to a problem in the copy mode of ffmpeg.

If it's really that, and if you just do ffmpeg copy one one file, you
won't probably hear it... even when two audio files that belong
together, you may need to listen *very* closely to hear a gap.


Cheers,
Chris.
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