[gentoo-user] Audio through second HDMI output on GPU?

[Arve Barsnes]

Hello,

Resending this message, as the last time it was derailed by a question
about DE and pulseaudio, neither of which are relevant to this
low-level problem (and also not installed anyway, as I run a simple
openbox WM with alsa only).

Does anyone know anything about how to check audio through Nvidia HDMI outputs?

My regular audio is through the motherboard output, and I also have a
USB soundcard that I regularly use without trouble, but my HDMI is a
different matter.

I have a GTX 1080 card with two HDMI outputs, the first connected to
my main monitor, and the second connected to a TV. I've managed to
play sound through my monitor with aplay, but no luck with the TV.

aplay reports:
$ aplay -l
card 1: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 8: HDMI 2 [HDMI 2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 9: HDMI 3 [HDMI 3]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 10: HDMI 4 [HDMI 4]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 11: HDMI 5 [HDMI 5]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 12: HDMI 6 [HDMI 6]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

To get sound through the monitor:
aplay -D plughw:1,7 sample.wav

No luck on any of the other 6 devices reported. I suspect there might
be a setting somewhere on the Nvidia side that limits sound output to
one of these, and if that is so, I'd rather have the TV able to get
sound, as my computer have separate speakers and no need for the HDMI
sound output.

Any ideas for troubleshooting this welcome.

Regards,
Arve