[mythtv-users] SOLVED: Re: Exasperated: DD/DTS SPDIF works with everything *except* MythTV

Kingsley Turner krt at krt.com.au
Sun Dec 7 10:39:47 UTC 2008

Allen Edwards wrote:
>>>>> I have configured Myth to use
>>>>>    "alsa:default" for audio,
>>>>> and "ALSA:iec958:{AES0 0x02}" as the SPDIF output device.
>>>>> Obviously the two checkboxes for sending AC3 and DTS sound out via SPDIF
>>>>> are checked.
>>>>> Mplayer works fine with: -ao alsa:device=iec958 hwac3
>>>>> VLC works fine with: --spdif    (oh, *so* easy!)
>>>> Have you tried just "alsa:iec958" in Myth?
>>> Rename or delete asound.conf and .asoundrc.
>>> Set the passthrough device to ALSA:iec958:{ AES0 0x02 }
>>> Audio output device to ALSA:spdif.
>>> If you are running Fedora, get rid of Pulse Audio (not
>>> trivial apparently).
>>> Turn on iec958 in alsamixer
>> This is basically what I have already, except using ALSA:default instead
>> of ALSA:spdif.
>> I tried "ALSA:spdif", and got the same result.
>> However I did notice that the digital sound (DD5.1 / playing DVD) seemed
>> to be dropping in and out (according to the LED on the amp. anyway) and
>> occasionally we'd get a split-second of sound before it dropped back to
>> silence.  After changing back to ALSA:default I notice this is happening
>> here also.  I'd guess it's not keeping up with the sound output or
>> something, maybe some kind of buffering thing ??!  ("Agressive Sound
>> card buffering" is turned OFF).
> Sorry, my reply was not complete:
> Output ALSA:spdif
> Passthrough device  ALSA:iec958:{ AES0 0x02 }
> max Audio: Stereo (other setting is broken)
> Upmix: Passive
> Aggressive: unchecked
> Internal Volume: I have it unchecked but I think it may work checked as well
> Enable AC3 and DTS both checked.
> Hopefully you didn't have max audio set to stereo and this will fix
> your problem
I already had this set to stereo, but I read somewhere else it doesn't 
effect digital out?

Anyway, I just solved it this second:

A quick little sentence in the MythTV wiki nailed it:


If "Use video as timebase" is checked, you will get stuttering audio 
output or not audio at all. "Use video as timebase" *must* be unchecked 
if you want AC3 audio to work.

Just an offhand sentence, but *so* important!

I don't know how I missed it, maybe because there's so many documents on 
this, after you read a few of them you start to gloss-over them, not 
reading properly.  Guess I was punished for my own lack of thoroughness.

Although, I wish the UI would give you a warning about this or 
something.... ;)

thanks to everyone for their help!


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