[mythtv-users] Alsa SPDIF SP13000 (via8237)

Michael T. Dean mtdean at thirdcontact.com
Mon Aug 14 11:29:54 UTC 2006

On 08/14/2006 12:48 AM, Robin Gilks wrote:
>> For the Via8237, it's device 0, subdevice 3.
> As stated, I've tried all combinations - I inferred that it was in fact
> 0,0,3 by using the -v flag on "aplay -D spdif ..." but that doesn't
> explain why
>   aplay -D spdif xxx.wav
> works OK but
>    aplay -D hw:0,0,3 xxx.wav
> doesn't work. Must be missing something (again!)
Because you need a valid ALSA configuration that allows for conversion 
of the sample rate, channels, and format to those required by your 
card.  I.e. you need to use the .asoundrc/asound.conf from the wiki ( 
) configured with:

# Alias for digital (S/PDIF) output on the card
# Do not use this directly--it requires specific rate, channels, and format
pcm.digital-hw {
  type hw
  card 0
  device 0
  subdevice 3

BTW, aplay -D hw:0,0,3 would likely fail even with AC-3/DTS passthrough 
because it doesn't properly configure the device.  Therefore, the ALSA 
devs created a built-in device name iec958 to do the required device 
configuration.  Since normal people don't care (don't remember) that an 
S/PDIF output is an IEC958 device, they also created a built-in alias 
called spdif to make it easy to access.

This lack of configuration is also the reason that the wiki ALSA config 
files will not work with AC-3/DTS (on all systems).  One of these days, 
I'll fix it.  (Maybe in September.)


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