[mythtv-users] ac3 passthrough problems

Nick knowledgejunkie at gmail.com
Wed Sep 20 03:24:20 UTC 2006

On 19/09/06, Scott <list-mythtv at bluecamel.eml.cc> wrote:
> I'd like to ask for some help, and sanity checking, trying to get AC3
> passthrough to work in 0.20. My video source is OTA ATSC and a Fusion
> HDTV5 RT. Audio is typically Dolby Digital 2 channel (stereo) or 5.1
> channel surround. I also have this card working with mplayer DVB and
> can confirm that my a/v receiver connected to the spdif correctly
> sees and accepts both DD 2.0 and DD 5.1 source from OTA ATSC
> broadcasts using "mplayer -ao alsa -afm hwac3 dvb://" So I'm fairly
> sure my alsa setup is configured correctly
> I found http://mythtv.org/wiki/index.php/Configuring_Digital_Sound
> which looks very helpful. I tried to set ALSA:default for my sound
> device but that doesn't work. Any suggestions on how I can get MythTV
> to send the raw AC3 stream out the spdif and to my A/V receiver?

If you specify ALSA:default as your MythTV passthrough sound device
and your default ALSA device is not your SPDIF, passthrough will not
work. You either need to specify your SPDIF directly in MythTV (like
ALSA:iec958 or ALSA:spdif) or you need to follow through the HOWTO
fully and adjust your asound.conf file to set your default ALSA device
to your SPDIF.

> See attached mplayer.log and mythtv.log. These two logs are of the
> same dvb stream which has DD 2.0 sound.

With mplayer, you are specifying the passthrough option in the run
command and it's working, which is good.

> Here is what aplay -l says about my Intel HDA audio:
> card 0: Intel [HDA Intel], device 0: AD198x Analog [AD198x Analog]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> card 0: Intel [HDA Intel], device 1: AD198x Digital [AD198x Digital]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0

If you do configure your asound.conf (or .asoundrc if using per user
settings) using the HOWTO you need to make sure you specify the
digital device as device 1 on card 0.

Note that aplay -L will give a list of PCM devices - towards the
bottom of the list of these devices will be the definition of the
'default' PCM device which usually the front analog output unless you
have specified otherwise.


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