[alsa-devel] S24_LE is 3 bytes ? in alsa-lib example pcm.c

[Takashi Iwai]

At Thu, 10 Jul 2008 12:41:39 +0200 (CEST),
Jaroslav Kysela wrote:
> 
> On Thu, 10 Jul 2008, Takashi Iwai wrote:
> 
> > At Thu, 10 Jul 2008 12:19:05 +0200 (CEST),
> > Jaroslav Kysela wrote:
> > > 
> > > On Thu, 10 Jul 2008, Clemens Ladisch wrote:
> > > 
> > > > Norbert van Bolhuis wrote:
> > > > > as far as I know:
> > > > > sample format S24_LE is 24bit sample in 4 bytes
> > > > > sample format S24_3LE is 24bit sample in 3 bytes
> > > > > (why else have separate definitions), right ?
> > > > 
> > > > Yes.
> > > > 
> > > > > In the ALSA-LIb example /test/pcm.c however
> > > > > (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html)
> > > > > there is no diff between the 2 sample formats.
> > > > 
> > > > That example program uses snd_pcm_format_width() although it should
> > > > have used snd_pcm_format_physical_width() when calculating memory
> > > > buffer sizes.
> > > 
> > > I think that the problem is in wrong area->step calculation in alsa-lib, 
> > > but I'm still investigating where the real culprit is. The
> > > snd_pcm_format_width() is used only for sample filling (which is OK).
> > 
> > I think Clemens is right.  The program uses snd_pcm_format_width()
> > wrongly.  Also, it won't work properly with strict aliasing...
> 
> Yes, the patch looks good. I overlooked that the area initialization is 
> directly in pcm.c code (I looked only to generate_sine(). I tested it and 
> it produces good samples. I'm getting some underruns on my notebook with 
> 24-bit formats (but it's probably different problem).

OK, committed now.


Takashi