Re: [Audacity-devel] aac exports somewhat broken on Windows

[<ga...@au...>]

| From Gale Andrews <ga...@au...>
| To aud...@li... 
| Subject [Audacity-devel] aac exports somewhat broken on Windows
> | From LRN <lr...@gm...> 
> | Mon, 20 Jul 2009 23:44:28 +0400
> | Subject: [Audacity-devel] aac exports somewhat broken on Windows
> > ga...@au... wrote:
> > > AAC exports are broken on Windows if you export with 
> > > no extension - you just get a small filesize, silent file of 
> > > the correct length. FFmpeg at command line is OK as
> > > per below. 
> 
> > This could be
> > 1) A bug in Audacity (broken libav* integration) - perfectly possible
> > 2) A bug in libav* aac encoder, which replaced libfaac - perfectly possible
> > 3) Both
> > 
> > Since commandline aac encoding with ffmpeg works correctly, i'm assuming
> > that it's mostly (1) (and (2) in the sense that aac encoder behavior
> > doesn't match libfaac). I don't know when i'll be able to fix that.
> > Meanwhile everything will work correctly with libavcodec built with
> > built-in aac encoder disabled (--disable-encoder=aac), which makes it
> > fall back to libfaac. I can pack another libav* win32 binary release, if
> > you want.
> 
> If you could do that LRN, that would be best I think. I'll then rebuild
> the FFmpeg installer with your new contents. 

Thanks for the new win32 package, LRN. Seems fine in testing.
The revised FFmpeg installer for Windows is now up on the 
FFmpeg FAQ page. Leland, will you have a chance to rebuild 
the FFmpeg installer for Mac some time?

And actually, using either Audacity 1.3.8 with libfaac, or your 
previous Win32 binaries from the 12th July at the command line 
(built-in AAC encoder), AAC exports at sample rates below 44100 Hz
are encoded at the correct sample rate, according to QuickTime and
iTunes. I had believed this to be a bug in FFmpeg, but it now seems
dBPowerAmp which I was using was misreporting sample rates.
Checking the exported file size confirms that.   

Upgrading to the built-in AAC encoder will probably get rid of the 
other bug where files exported at 38000 Hz don't play properly. At 
the command line, AAC now just ignores 38000 Hz and exports at 
44100 Hz anyway, and the files play fine. 

However I think there is a bug with our AAC sample rate selection in
Audacity. If you choose 48000 Hz project rate I'd expect Audacity 
to fall back to the nearest supported rate below (44100 Hz), but it 
falls back to 38000 Hz, which is currently always going to export 
files which may not play. It looks if it's falling back to the wrong
rate because 38000 is out of order in the rate list. Could you just 
remove 38000, given you can't fix Audacity to use the AAC encoder
in the near future, and given built in AAC encoder now does not 
seem to support it anyway?


Thanks


Gale