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

[Mark Knecht]

On Fri, May 21, 2021 at 3:11 PM Arve Barsnes <arve.barsnes@×××××.com> wrote:
>
> On Fri, 21 May 2021 at 22:47, Mark Knecht <markknecht@×××××.com> wrote:
> > On Thu, May 20, 2021 at 2:35 AM Arve Barsnes <arve.barsnes@×××××.com>
wrote:
> > > 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).
> >    I'm very sorry that when you asked this question a month ago you
didn't like my answer. It was never my intention to 'derail' your question
with DE or pulseaudio. That said no one else has answered that question nor
have they responded to this one that you posted yesterday. I think you are
in a fairly unique setup that most people don't deal with but it is an
interesting area. I'd still like to help if I can.
>
> Maybe derailed was a little harsh. I was appreciative of your answer
> either way, as I might have left out some necessary information to
> make you ask about those things. This is still very low level as far
> as I understand it, so I'm not completely sure how to ask about what
> I'm wondering :)
>
> >
> >    To start please run the following command and let's see what ALSA
tells us:
> >
> > cat /proc/asound/card*/eld#0.*
>
> There was 16 of these entries, /proc/asound/card1/eld#0.4 was my Acer
> monitor which I managed to get sound through with my command:
> aplay -D plughw:1,7 sample.wav
>
> Most of the others simply showed:
> monitor_present         0
> eld_valid               0
>
> The connected TV was here:
> # cat /proc/asound/card1/eld#0.0
> monitor_present         1
> eld_valid               1
> monitor_name            TOSHIBA-TV
>
> connection_type         HDMI
> eld_version             [0x2] CEA-861D or below
> edid_version            [0x3] CEA-861-B, C or D
> manufacture_id          0x6252
> product_id              0x108
> port_id                 0x400
> support_hdcp            0
> support_ai              0
> audio_sync_delay        62
> speakers                [0xffff] FL/FR LFE FC RL/RR RC FLC/FRC RLC/RRC
> FLW/FRW FLH/FRH TC FCH
> sad_count               2
> sad0_coding_type        [0x1] LPCM
> sad0_channels           2
> sad0_rates              [0xe0] 32000 44100 48000
> sad0_bits               [0xe0000] 16 20 24
> sad1_coding_type        [0x2] AC-3
> sad1_channels           6
> sad1_rates              [0xe0] 32000 44100 48000
> sad1_max_bitrate        640000
>
> All of this is quite cryptic to me, so if you can glean any useful
> information from it that would be great. The monitor output is fairly
> similar if you exclude the sad1*-lines at the end, the most prominent
> difference being the speakers line, which only listed '[0x1] FL/FR'
>
> Regards,
> Arve

OK, it's a good sign that the NVidia card is talking to the TV and
providing reasonable data.

A monitor would support stereo, so FL/FR -> Front left, Front right

Your TV is going to support lots of different speakers via (potentially)
some 5.1, 7.1, 9.1 sound system you might have attached. The values you can
decode mentally but they are rear channels, center channel, stuff like that.

OK, so what does alsamixer tell you? On my system I hit F6, choose the card
and then F3 for Playback. I see the 7 channels. Hitting 'M' changes the
mute setting but all the volumes are at 0 and hitting '+' doesn't raise the
volume. It's been so long since I looked at spdif stuff that I don't
remember if spdif supports volume this way. Will research a bit.

Anyway, I _think_ that if you hit F2 (system info) and then choose
/proc/asound/pcm you will get a list of all the sound devices with the
numbers on the left being the plughw values, but I could be quite wrong
about that.

The problem right now is we don't know if the channel is transmitting at a
volume of 0, not transmitting at all, or possibly the TV is receiving audio
data but not accepting it due to format issues.

I see a response from eric so I would certainly look into what he's
pointing you toward.