[mythtv-users] Audio or ALSA bug?

[Jean-Yves Avenard]

Hi

On 22 August 2010 11:23, Douglas Choma <doug at polaritylabs.com> wrote:
>  I can't tell if this is a bug or if I'm just lame (maybe both?).
>
> I'm running r25379 from trunk.
>
> For my "Audio output device" I've selected "ALSA:iec958:CARD=NVidia,DEV=0"
> Speaker configuration: "5.1"
> I've also checked Dolby and DTS decoding
>
> And I had (this is the part that drove me crazy) "Use internal volume
> control" checked.  This setting is on the screen after the initial audio
> device settings.
>
> With the "Use internal volume control" active, I would get no audio and tons
> of errors on the frontend...
> ####
> AO: Original codec was AC3, signed 16 bit, 48 kHz, 6 channels
> AO: Opening audio device 'iec958:CARD=NVidia,DEV=0' ch 6(6) sr 48000 sf
> signed 16 bit reenc 1
> ALSA: Setting IEC958 status: audio
> Opening ALSA audio device 'iec958:CARD=NVidia,DEV=0'.
> ALSA: SetParameters(format=2, channels=6, rate=48000, buffer_time=100000,
> period_time=50000)
> ALSA, Error: Channels count 6 not available: Invalid argument
> ALSA, Error: Unable to set ALSA parameters: Invalid argument
> AudioOutput Error: Aborting reconfigure
> ALSA, Error: getBufferedOnSoundcard() called with pcm_handle == NULL!
> ALSA, Error: getBufferedOnSoundcard() called with pcm_handle == NULL!
> ALSA, Error: getBufferedOnSoundcard() called with pcm_handle == NULL!
> ALSA, Error: getBufferedOnSoundcard() called with pcm_handle == NULL!
> ... repeats until crash ...
> ####
>
> As soon as I turned that setting off, audio worked and no more errors.
>
> So my questions...
> 1) Should it be possible to select settings that cause such serious errors
> (crashes)?  I know the wiki mentions turning that off for digital output;
> but it seems like maybe that setting shouldn't be available if it's
> incompatible with settings on the previous page?
> or
> 2) Do I just have something really wrong with my ALSA configuration?
>

It looks like ALSA is reporting 6 channels for the audio device, when
really two is only supported.
Did you press the Scan button and then choose the device in the list?

The other possibility is that you checked the "Multi-PCM" flag, when
you shouldn't as SPDIF doesn't support multi-PCM audio, only stereo
and AC3 / DTS

JY