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

Kingsley Turner krt at krt.com.au
Sat Dec 6 17:26:39 UTC 2008


Upgraded my motherboard to a Gigabyte E7AUM-DS2H today; but that's 
beside the point, I think I had this problem before the upgrade, and 
stupidly hoped it would help.

Anything with a DD or DTS digital audio stream (HDTV channels and DVD 
playback) is in a world of FAIL.

I've spent all day (since 6am this morning) trawling though doco, mail 
posts from 2005, etc. etc.  I just can't seem to work out what's wrong.  
I'm pulling my hair out, and the kids wont come near me for fear of 
being snapped at.

Basically the problem is that any sort of dolby digital (or DTS) signal 
goes out over SPDIF incorrectly or goes out without volume (no iec958 
isn't muted).  The display on the amp shows a DD (or DTS) stream is 
happening, but there's no sound.  However VLC can play DVDs with DD5.1 
and DTS perfectly, mplayer can do the same.  It's only myth that's 
exhibiting the problem.

After playing with lots of /etc/asound.conf configurations, now I have 
none (which seems to work best), and is recommended by the alsa wiki, 
and in a few other places. 

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!)

Since the first thing asked for is "aplay -L" here it is:

kingsley at mediabox:~$ aplay -L
    HDA NVidia, ALC885 Analog
    Default Audio Device
    HDA NVidia, ALC885 Analog
    Front speakers
    HDA NVidia, ALC885 Analog
    4.0 Surround output to Front and Rear speakers
    HDA NVidia, ALC885 Analog
    4.1 Surround output to Front, Rear and Subwoofer speakers
    HDA NVidia, ALC885 Analog
    5.0 Surround output to Front, Center and Rear speakers
    HDA NVidia, ALC885 Analog
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
    HDA NVidia, ALC885 Analog
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
    HDA NVidia, ALC885 Digital
    IEC958 (S/PDIF) Digital Audio Output
    HDA NVidia
    HDMI Audio Output

The log isn't showing anything too untoward, it logs where it opens the 
audio device without any hint of errors.

2008-12-06 18:19:41.116 AFD: codec AC3 has 0 channels
2008-12-06 18:19:41.117 AFD: Opened codec 0xa8eb7930, id(AC3) type(Audio)
2008-12-06 18:19:41.119 Opening audio device 'default'. ch 2(2) sr 48000
2008-12-06 18:19:41.119 Opening ALSA audio device 'iec958:{ AES0 0x02 }'.
2008-12-06 18:19:41.134 NVP: Enabling Audio
2008-12-06 18:19:41.136 Opening audio device 'default'. ch 2(2) sr 48000
2008-12-06 18:19:41.136 Opening ALSA audio device 'iec958:{ AES0 0x02 }'.

All audio goes out through SPDIF to an amplifier.  As I've already said, 
Myth plays tv with mpeg audio fine, mplayer/vlc play anything with 
DD/DTS/mpeg audio fine.  But MythTV wont play DD/DTS audio.

*Please*   Any sage advice?


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