At Sun, 3 Mar 2013 20:29:22 +0100, Torstein Hegge wrote:
On Sat, Mar 02, 2013 at 02:12:33PM +0100, Daniel Mack wrote:
On 02.03.2013 14:04, Torstein Hegge wrote:
The C-Media CM6631 USB-to-S/PDIF receiver doesn't respond to changes in sampling frequency while the interface is active.
Reset the interface after setting the sampling frequency, to ensure that the sample rate set by snd_usb_init_sample_rate() is used. Otherwise, the device will try to use the sample rate of the previous file, causing distorted sound on sample rate changes.
Signed-off-by: Torstein Hegge hegge@resisty.net
Acked-by: Daniel Mack zonque@gmail.com
While this does fix the sample rate change problem, it introduces a new problem. With at least one media player application (xbmc) this patch causes the usb sound card to not output sound when starting a video file. Skipping forward or backward in the video stream restores audio output.
I haven't yet been able to look into why this happens, or why xbmc behaves different from mplayer and vlc.
If the reset of interface is needed only when *changing* SRC, we can check the current rate against the previous rate and skip the reset?
The difference of xbmc and mplayer/vlc may come from the different initialization procedure. Apps can call hw_params or prepare multiple times, for example, before actually starting the stream.
Takashi
Torstein
sound/usb/pcm.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c index d82e378..01978a6 100644 --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -710,6 +710,16 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream) subs->need_setup_ep = false; }
- /* Some devices doesn't respond to sample rate changes while the
* interface is active. */- switch (subs->stream->chip->usb_id) {
- case USB_ID(0x0d8c, 0x0304): /* C-Media - Schiit USB Interface */
- case USB_ID(0x0d8c, 0x0309): /* C-Media CM6631 */
usb_set_interface(subs->dev, subs->cur_audiofmt->iface,subs->cur_audiofmt->altset_idx);break;- }
- /* some unit conversions in runtime */ subs->data_endpoint->maxframesize = bytes_to_frames(runtime, subs->data_endpoint->maxpacksize);
Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel