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#1 2023-02-26 03:36:18

klugja
Member
Registered: 2023-02-20
Posts: 13

[SOLVED] Trying to get IEC958 pass through to work with MythTV and VLC

I have IEC958 working in two channel mode using wireplumber.  Is it incompatible with running MythTV and VLC in pass through?  I get no audio if I select pass through and IEC958.  VLC is a bit strange in that it lists two IEC958 entries, but neither work.

On my old PC running much older software I used pulseaudio for Firefox and other audio applications, and IEC958 pass through for MythTV and VLC to get DTX and Dolby Surround (I have a receiver with S/PDIF).

Unfortunately I can only get IEC958 working through wireplumber:

From wpctl status:

Audio
   Sinks
      *   79. USB Audio S/PDIF Output             [vol: 1.00]

Settings
  Default Configured Node Names:
         0. Audio/Sink    alsa_output.usb-Generic_USB_Audio-00.pro-output-2

In alsamixer, if I select USB Audio (card 2), there is no IEC958 available.  There is a PCM1, and a PCM2 (PCM2 seems to be stuck at 0).

What is the correct way to get all my applications working correctly?  I assume most applications don't support pass through, but now nothing does pass through.

aplay -L lists two SPDIF outputs, just like VLC:

iec958:CARD=Audio,DEV=0
    USB Audio, USB Audio
    IEC958 (S/PDIF) Digital Audio Output
iec958:CARD=Audio,DEV=1
    USB Audio, USB Audio #1
    IEC958 (S/PDIF) Digital Audio Output

Last edited by klugja (2023-03-01 06:42:25)

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#2 2023-02-26 16:02:43

klugja
Member
Registered: 2023-02-20
Posts: 13

Re: [SOLVED] Trying to get IEC958 pass through to work with MythTV and VLC

Maybe this is a driver bug:

I ran strace, with this option:

-Diec958:CARD=Audio,DEV=1

and I see:

openat(AT_FDCWD, "/dev/snd/controlC2", O_RDWR|O_CLOEXEC) = 3
...
openat(AT_FDCWD, "/dev/snd/pcmC2D999p", O_RDWR|O_NONBLOCK|O_CLOEXEC) = -1 ENOENT (No such file or directory)

Resulting in:

aplay: main:831: audio open error: No such file or directory

So maybe the 2nd iec958 channel is not correct in the driver. I have the Realtek ALC4080 on my mother board, and I read that the 2nd IEC958 port is being used, not the first.

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#3 2023-03-01 06:41:24

klugja
Member
Registered: 2023-02-20
Posts: 13

Re: [SOLVED] Trying to get IEC958 pass through to work with MythTV and VLC

I set mythtv and VLC to use ALSA:pipewire as their device.

In VLC:
Tools->Preverences->Audio Settings:
  Output module: ALSA audio output
  Use S/PDIF when available
  Device: PipeWire Sound Server

Audio->Audio Device Select "PipeWire Sound Server"

In pavucontrol I had to select the profile for my sound device. I selected USB Audio->HiFi 7.1 profile on the configuration page, deselected all the other profiles,  and only S/PDIF showed up on the output devices and playback tabs.

The volume control should not be available, but it is.  With an AC3 signal, If you change the volume from exactly 100%, the sound turns into very loud noise.

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