On Wed, 16.07.08 16:30, Lennart Poettering (mznyfn@0pointer.de) wrote:
Heya!
With 1.0.17rc3 snd_pcm_rewind() is broken for softvol as it seems:
Sometimes the sound becomes heavily distorted after such a seek:
http://mailman.alsa-project.org/pipermail/alsa-devel/2008-June/008860.html
And snd_pcm_rewind() might return a value that is higher than was passed in, which as far as I understood should never happen:
http://mailman.alsa-project.org/pipermail/alsa-devel/2008-April/007308.html
These two issues might be caused by the same error.
Takashi, Jaroslav, how can I bribe you into fixing this? I'd love to release my new PulseAudio version soon which heavily relies on snd_pcm_rewind(), but unfortunately the most important driver (hda with softvol) makes the most problems with it. :-(
Hmm, if I understand snd_pcm_plugin_rewind() in pcm_plugin.c correctly, then I read it like this:
1. we clamp the input frames to hw_avail 2. we convert this to slave frames 3. we issue the rewind 4. we convert back to client frames 5. we return hw_avail.
Step #1 seems wrong to me. The code will make sure that we rewind as least as much as can be written right now. Does that make any sense? I don't think so. Shouldn't this be a clamp that makes sure that we rewind at most as much as the buffer is filled right now? I.e. something along the lines of:
if (frames > buffer_size - n) frames = buffer_size - n;
Also, step #5 seems wrong to me. Shouldn't we return the result of the second conversion? I.e. shouldn't "return n" be replaced by "return (snd_pcm_sframes_t) frames"?
I am puzzled though, not sure if I understood that function correctly at all.
Lennart