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

[Andreas Cadhalpun]

Control: tags -1 - moreinfo + confirmed

Hi,

On 19.12.2015 21:09, Christoph Anton Mitterer wrote:
> 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.

OK, so the problem is that after remuxing with ffmpeg, there is
a barely audible ... gap ... between the two files, right?

Now I'm a bit skeptical about "LAME adding some special tags".
You've used lame with '--id3v2-utf16 --add-id3v2 --id3v1-only'.
What is this supposed to do? Add id3v1 tags, or id3v2 or both?

Additionally it seems the created files contain neither.
And leaving out these id3 options doesn't change the output
from lame.

So I'm not sure how this is supposed to work.

Best regards,
Andreas