[mythtv-users] ALSA:surround51 with MythTV 0.24

Achim Hofmann news at achim-hofmann.com
Sun Mar 6 20:00:13 UTC 2011


Today I updated my MythBox from 23.1 to 0.24.20101129-1 using the gentoo
ebuilds provided on MythTV github:

https://github.com/MythTV/packaging/tree/master/Gentoo

As described in the release notes for 0.24, the audio subsystem has been
rewitten. Resulting from this, the ALSA surround51 pcm device doen't
work for me anymore within MythTV (no matter which speakers
configuration, 2.0/stereo or 5.1). However, the ALSA default pcm device
(which only provides 2.0/stereo) still works fine.

In my MythBox there's a VIA Technologies, Inc. VT8233/A/8235/8237 AC97
Audio Controller (rev 60). This is the output of `aplay -L`:

null
    Discard all samples (playback) or generate zero samples (capture)
default:CARD=V8237
    VIA 8237, VIA 8237
    Default Audio Device
front:CARD=V8237,DEV=0
    VIA 8237, VIA 8237
    Front speakers
surround40:CARD=V8237,DEV=0
    VIA 8237, VIA 8237
    4.0 Surround output to Front and Rear speakers
surround41:CARD=V8237,DEV=0
    VIA 8237, VIA 8237
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=V8237,DEV=0
    VIA 8237, VIA 8237
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=V8237,DEV=0
    VIA 8237, VIA 8237
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
iec958:CARD=V8237,DEV=0
    VIA 8237, VIA 8237
    IEC958 (S/PDIF) Digital Audio Output

When set to ALSA:surround51:CARD=V8237,DEV=0 and playing a movie, the
following error appears in mythfrondend.log:

2011-03-06 12:31:18.479 AFD Warning: ScanATSCCaptionStreams() called
with no PMT
2011-03-06 12:31:18.480 AFD: Opened codec 0xb3c04a0, id(MPEG2VIDEO)
type(Video)
2011-03-06 12:31:18.480 AFD: codec AC3 has 6 channels
2011-03-06 12:31:18.481 AFD: Opened codec 0xb387cb0, id(AC3) type(Audio)
2011-03-06 12:31:18.607 AO: Opening audio device
'surround51:CARD=V8237,DEV=0' ch 6(6) sr 48000 sf signed 16 bit reenc 0
2011-03-06 12:31:18.617 ALSA, Error: Error opening
/proc/asound/card0/pcm1p/sub0/prealloc. Fix reading permissions.
2011-03-06 12:31:18.617 ALSA, Error: Unable to sufficiently increase
ALSA hardware buffer size - underruns are likely
2011-03-06 12:31:18.635 AudioPlayer: Enabling Audio

The audio sounds heavy scratched.

When set to ALSA:default:CARD=V8237 there are no errors and the audio is
fine. Of course, it's downmixed to 2.0/stereo now.

Here's the complete content of folder /proc/asound/card0:

dr-xr-xr-x 2 root root 0  6. Mär 20:43 codec97#0
-r--r--r-- 1 root root 0  6. Mär 20:43 id
-rw-r--r-- 1 root root 0  6. Mär 20:43 oss_mixer
-r--r--r-- 1 root root 0  6. Mär 20:43 via82xx

So there's no folder called "pcm1p". I've no idea why MythTV tries to
handle with it?

By the way: Using mplayer with the ALSA surround51 pcm device still
works fine. Only using the MythTV internal player makes trouble.

Any suggestions?

Regards,
Achim Hofmann


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