Mailing List Archive

ac3 passthrough problems
I'd like to ask for some help, and sanity checking, trying to get AC3
passthrough to work in 0.20. My video source is OTA ATSC and a Fusion
HDTV5 RT. Audio is typically Dolby Digital 2 channel (stereo) or 5.1
channel surround. I also have this card working with mplayer DVB and
can confirm that my a/v receiver connected to the spdif correctly
sees and accepts both DD 2.0 and DD 5.1 source from OTA ATSC
broadcasts using "mplayer -ao alsa -afm hwac3 dvb://" So I'm fairly
sure my alsa setup is configured correctly

I found
which looks very helpful. I tried to set ALSA:default for my sound
device but that doesn't work. Any suggestions on how I can get MythTV
to send the raw AC3 stream out the spdif and to my A/V receiver?

See attached mplayer.log and mythtv.log. These two logs are of the
same dvb stream which has DD 2.0 sound.

Here is what aplay -l says about my Intel HDA audio:

card 0: Intel [HDA Intel], device 0: AD198x Analog [AD198x Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: Intel [HDA Intel], device 1: AD198x Digital [AD198x Digital]
Subdevices: 1/1
Subdevice #0: subdevice #0

ac3 passthrough problems [ In reply to ]
On Sat, 2006-09-30 at 16:57 -0400, Richard Krehbiel wrote:
> I'm building a mythtv system now (about as slowly as anyone possibly
> can), and I'm stumped on the S/PDIF problem.
> I have an MSI K9NGM2-FID - Socket AM2, nVidia GeForce 6150, and I'm
> using on-board sound with Intel HDA drivers (snd-intel-8x0). I
> installed Fedora Core 5, current updates...

I'm in much the same position, right down to the "slowly" part. My system is
an MSI K8NGM2 (the Socket 939 variant) with a GeForce 6150, nForce 430, and a
Realtek ALC880, running Ubuntu 6.06 and alsa 1.0.10. "aplay -l" prints
**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 0: ALC880 Analog [ALC880 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 2: ALC880 Digital [ALC880 Digital]
Subdevices: 1/1
Subdevice #0: subdevice #0
The output of "aplay -L" is identical to his.

A file in my /etc/modprobe.d directory contains
alias snd-card-0 snd_hda_intel
options snd-card-0 index=0
options snd_hda_intel index=0
options snd_hda_intel model=3stack-digout

In alsamixer, "IEC958" is not muted. (I don't see a graph bar above
it.) "PCM" is set to 90, "Surround", "Center", and "LFE" are set at 100, "PC
Speak" is set at 97, and none are muted. "Channel" is set to "6ch".
The "Playback" view also includes "Headphon", "Front
Mi", "Line", "CD", "Mic", and three "Input So" devices, which seems weird to

I used "speaker-test" to test sound with no .asoundrc file.
- "speaker-test -c2" produces hisses from my front left and front right
speakers in turn, as expected.
- "speaker-test -c6" prints messages ending in "0 - Front Left", and pauses
- "speaker-test -Dspdif" prints "Playback open error: -2,No such file or
directory" repeatedly. Note that "aplay -L" output included a line that
said "spdif 'cards.pcm.iec958'". Can anyone suggest what file it wants to
open -- something under /dev/snd, perhaps?
- "aplay /usr/share/sounds/alsa/Front_Left.wav" produces sound on all six
speakers. Is that what should happen?
- "aplay /usr/share/sounds/alsa/Front_Left.wav -Dspdif" produces the error
message "aplay: main:544: audio open error: No such file or directory".

I tried the .asoundrc file from, modified so
that contains "device 2". With that set-up,
- "speaker-test -c6 -Dmixed-analog" produces hisses from the front left and
right speakers. Speaker-test *claims* that it is sending sound to the other
four speakers, but I hear nothing. The display on my receiver shows "PCM 48"
when the left and right front are hissing, and nothing when the other four
speakers should be taking their turns. The display also suggests that the
receiver is only getting left, right, center, and subwoofer channels.
- "speaker-test -c6 -Dmixed-digital" produces a hiss on the front left
speaker, a hideous noise on the front right, and silence on the other four.
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