[FFmpeg-devel] [PATCH 0/5] Fix mp3 gapless support (second try)

[Michael Niedermayer]

On Wed, Apr 15, 2015 at 01:16:45PM +0200, wm4 wrote:
> On Wed, 15 Apr 2015 12:42:04 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > On Wed, Apr 15, 2015 at 11:08:02AM +0200, wm4 wrote:
> > > On Tue, 14 Apr 2015 22:44:22 +0200
> > > Michael Niedermayer <michaelni at gmx.at> wrote:
> > > 
> > > > On Tue, Apr 14, 2015 at 09:24:32PM +0200, wm4 wrote:
> > > > > Seeking was slightly broken. The 4th patch seems to fix this (everything
> > > > > else is noise).
> > > > > 
> > > > 
> > > > > Note that ffmpeg can't correctly implement mp3 gapless audio if seeking
> > > > > is used. The xing toc is not precise enough. The only way to fix it is
> > > > > to do a full scan on the mp3 to index each frame (which in turn is not
> > > > > possible with the public API, because byte seeking is not supported and
> > > > > the parser would interfere anyway). But in this case, it even broke when
> > > > > seeking to the beginning. I'm still not sure if this patch is correct.
> > > > 
> > > > do you have a file/sample/testcase for patch 4 ?
> > > 
> > > https://0x0.st/AG.mp3
> > > 
> > > I'm assuming mpg123 is getting it right. One test case is seeking to
> > > the start of the file. (Seeking to anywhere else likely won't work,
> > > because libavformat tries to use the imperfect xing toc, instead of
> > > scanning the frames.)
> > 
> > how can this be tested ?
> > ./ffmpeg -ss 0 -i AG.mp3  -flags +bitexact new.wav
> > ./ffmpeg-ref -ss 0 -i AG.mp3  -flags +bitexact old.wav
> > 
> > 52298dcb38185e665b1b6d184884dd3e  new.wav
> > 52298dcb38185e665b1b6d184884dd3e  old.wav
> > 
> > ./ffmpeg -ss 5 -i AG.mp3  -flags +bitexact new.wav
> > ./ffmpeg-ref -ss 5 -i AG.mp3  -flags +bitexact old.wav
> > 
> > b4b8f2a83924b48f3d25baa6b9b4f4a8  new.wav
> > b4b8f2a83924b48f3d25baa6b9b4f4a8  old.wav
> 
> The result is the same because in both cases the CBR seeking path is
> used, which didn't change. You need to apply patch 5/5. I don't have a
> good "real" VBR sample at hand for testing, unfortunately.

ok, i can confirm that seek to 0 works better with the patches 3&4
with xing TOC
so applied them

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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