[mythtv-users] Audio upmixing problems

[Miah Gregory]

Hi,

I recently decided to use my soundcards ability to output some form of
5.1 analog audio, with the three 3.5mm stereo sockets on the sound card
being connected to an appropriate analog input amplifier.

I am running 0.21 from the debian feed on www.debian-multimedia.org.

The settings for audio are as follows:

Audio output device: ALSA:surround51:CARD=V8237,DEV=0
Passthrough output device: Default
Max Audio Channels: 5.1
Upmix: Active Linear
AC3 to SPDIF passthrough: disabled
DTS to SPDIF passthrough: disabled
Aggressive Sound card Buffering: disabled
Use internal volume controls: enabled
Mixer Device: ALSA:CARD=V8237
Mixer Controls: Master

These settings work perfectly for mythmusic, but when I try to play back
a recording, there is no audio.

Experimenting with various values on the page, the key one seems to be
upmix; when set to passive, I get audio with recordings, but when set to
either of the active methods, there is no audio.

Follows is a log extract from the front end with -v audio set:

-snip-
XMLParse::LoadTheme using /usr/share/mythtv/themes/Iulius/ui.xml
TV: Attempting to change from None to WatchingPreRecorded
AFD: Opened codec 0x881c4d0, id(MPEG2VIDEO) type(Video)
AFD: codec MP2 has 2 channels
AFD: Opened codec 0x881cbd0, id(MP2) type(Audio)
AFD: Audio Track #1 is A/V stream #2 and has 2 channels in the
Undetermined language(7695972).
AFD: Selected track 1: Undetermined MP2 2ch (A/V Stream #2)
AFD: Initializing audio parms from audio track #1
AFD: Audio format changed 
from id(NONE)    -1Hz -1ch   0bps    ; id(NONE)    -1Hz -1ch   0bps   
to   id( MP2) 48000Hz  2ch  16bps    ; id( MP2) 48000Hz  2ch  16bps   
AO: Needs upmix
AO: Killing AudioOutputDSP
Opening audio device 'jack51'. ch 6(2) sr 48000
Opening ALSA audio device 'jack51'.
in SetParameters(format=2, channels=6, rate=48000, buffer_time=500000,
period_time=125000)
get_buffer_size returned 5461
set_period_time_near returned 2645
get_period_size returned 127
Opening mixer jack51
Setting Master volume to 70
Volume range is 0 to 31, mult=3.22581
channel 0 vol set to 22
ALSA: channel 0 playback switch set to 1
Setting Master volume to 70
Volume range is 0 to 31, mult=3.22581
channel 1 vol set to 22
ALSA: channel 1 playback switch set to 1
Setting PCM volume to 81
Volume range is 0 to 31, mult=3.22581
channel 0 vol set to 25
ALSA: channel 0 playback switch set to 1
Setting PCM volume to 81
Volume range is 0 to 31, mult=3.22581
channel 1 vol set to 25
ALSA: channel 1 playback switch set to 1
Volume range is 0 to 31, mult=3.22581
AO: Audio fragment size: 6144
AO: create upmixer
AO: create upmixer done with surround mode 1
AO: Audio Stretch Factor: 1
Audio Codec Used: not set
AO: kickoffOutputAudioLoop: pid = 28769
AO: OutputAudioLoop: Play Event
AO: Ending reconfigure
AO: Needs upmix
AO: no change exiting
AO: Needs upmix
AO: no change exiting
AO: Pause 1
AO: OutputAudioLoop: audio paused
VideoOutputXv: XVideo Adaptor Name: 'NV04 Video Overlay'
OSD Theme Dimensions W: 640 H: 480
TV: Changing from None to WatchingPreRecorded
AO: Pause 1
AO: OutputAudioLoop: audio paused
Using realtime priority.
OpenGLVideoSync()
WriteAudio: buffer underrun
Video timing method: SGI OpenGL
AO: Pause 0
AO: OutputAudioLoop: Play Event
TV: Attempting to change from WatchingPreRecorded to None
~OpenGLVideoSync() -- begin
~OpenGLVideoSync() -- middle
~OpenGLVideoSync() -- end
AO: Killing AudioOutputDSP
AO: OutputAudioLoop: Stop Event
AO: kickoffOutputAudioLoop exiting
TV: Changing from WatchingPreRecorded to None
-snip-

Having compared the logs, the key line that seems to change is:

AO: create upmixer done with surround mode [012]

The buffer overrun message seen above does not always occur, and I have
only ever seen one, rather than it being repeated as you might expect if
the buffer is being starved.

Any thoughts or suggestions welcome - it would be good to get this
working.

Thanks.

-- 
Miah Gregory