[mythtv-users] Not the usual problem with digital passthrough.

[Robert Jones]

Hi, everyone.

I decided yesterday that I was going to do away with my standalone DVD
player and allow myth to take over that role in my entertainment
center.  However, I ran into some bizarre issues getting audio to
passthrough to my home theater receiver.

I'm currently running Ubuntu Gutsy, tracking the Mythbuntu weekly
builds of the svn trunk.  My system has MCP51 onboard audio, using the
hda-intel drivers manually updated to the latest ALSA beta (although
this also occured with earlier versions).
I'm pulling digital out via S/PDIF.

My audio out and digital passthrough are both currently set to ALSA:iec958.

I can get full dolby digital to my amp using mplayer, by routing sound
to ALSA:iec958 and forcing hwac3.  However, when I try to play the
same DVD through myth, the audio I get is raw digital noise.  It's
almost as though the bitstream is being sent down the wire as plain
PCM audio.

I have tried jiggering the output devices.  using ALSA:plug:iec958
doesn't change anything.  Nor do any of the AESx hex incantations that
I have seen scattered about -- they either break audio entirely, or do
nothing to change the presentation of raw digital noise.  Accessing
hw:0,1 doesn't help, either.

(And, yes, I'm set to AC3 and DTS passthrough, and "use video as
timebase" is off.)

For reference, here's the output of aplay -l:

**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 0: AD198x Analog [AD198x Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 1: AD198x Digital [AD198x Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0





Here's aplay -L:

default:CARD=NVidia
    HDA NVidia, AD198x Analog
    Default Audio Device
front:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Analog
    Front speakers
surround40:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Analog
    4.0 Surround output to Front and Rear speakers
surround41:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Analog
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Analog
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Analog
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Analog
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=NVidia,DEV=0
    HDA NVidia, AD198x Digital
    IEC958 (S/PDIF) Digital Audio Output
null
    Discard all samples (playback) or generate zero samples (capture)




And here's a portion of my frontend log (from a title screen, so it's
only 2-channel AC3, but 6-channel looks similar, and both sound the
same), with -v audio turned on.:



2008-02-28 02:45:40.997 AFD: Opened codec 0xaa6ef030, id(AC3) type(Audio)
2008-02-28 02:45:40.998 AFD: Audio Track #1 is A/V stream #1 and has 0
channels in the Undetermined language(7695972).
2008-02-28 02:45:41.007 AFD: Selected track 1: Undetermined LIBA52 2ch
(A/V Stream #1)
2008-02-28 02:45:41.008 AFD: Initializing audio parms from audio track #1
2008-02-28 02:45:41.008 AFD: Audio format changed digital passthrough
id( AC3) 48000Hz  2ch  16bps pt
                        from id(NONE)    -1Hz -1ch   0bps    ;
id(NONE)    -1Hz -1ch   0bps
                        to   id( AC3) 48000Hz  2ch  16bps pt ; id(
AC3) 48000Hz  2ch  16bps pt
2008-02-28 02:45:41.019 AO: Needs upmix
2008-02-28 02:45:41.019 AO: Killing AudioOutputDSP
2008-02-28 02:45:41.019 Opening audio device 'plug:iec958'. ch 6(2) sr 48000
2008-02-28 02:45:41.020 Opening ALSA audio device 'plug:iec958'.
2008-02-28 02:45:41.032 in SetParameters(format=2, channels=6,
rate=48000, buffer_time=100000, period_time=25000)
2008-02-28 02:45:41.034 get_buffer_size returned 4800
2008-02-28 02:45:41.034 set_period_time_near returned 20000
2008-02-28 02:45:41.034 get_period_size returned 960
2008-02-28 02:45:41.050 AO: Audio fragment size: 19200
2008-02-28 02:45:41.052 AO: create upmixer
2008-02-28 02:45:42.135 AO: create upmixer done with surround mode 2
2008-02-28 02:45:42.136 AO: Audio Stretch Factor: 1
2008-02-28 02:45:42.136 Audio Codec Used: not set
2008-02-28 02:45:42.136 AO: Ending reconfigure
2008-02-28 02:45:42.136 NVP: Enabling Audio
2008-02-28 02:45:42.136 AO: Killing AudioOutputDSP
2008-02-28 02:45:42.136 AO: kickoffOutputAudioLoop: pid = 16227
2008-02-28 02:45:42.136 AO: OutputAudioLoop: Stop Event
2008-02-28 02:45:42.136 AO: kickoffOutputAudioLoop exiting



I can provide more extensive logs if necessary, but I feel as though
I'm missing something glaringly obvious. :(


-- 
You have been eaten by a grue.