Dual mono setup doesn't work because two clients can't open dmix pcm devices

[rvk]

I have dual mono setup with Hifiberry sound cards in four rooms. This has worked with Snapcast and I was trying to switch to Sendspin, but two daemons can't simultaneously open PCM devices, even though allowed by ALSA. When one is active --list-audio-devices on the other returns an empty list.

Here's /etc/asound.conf for reproducing the issue:

pcm.hifiberry_raw {
type hw
card 0
device 0
}

pcm.hifiberry {
type plug
slave.pcm "hifiberry_raw"
}

pcm.dmixer {
type dmix
ipc_key 1024
slave {
pcm "hifiberry_raw"
channels 2
}
}

pcm.olohuone {
type plug
slave.pcm "dmixer"
ttable.0.0 1
ttable.1.0 1
ttable.0.1 0
ttable.1.1 0
}

pcm.keittio {
type plug
slave.pcm "dmixer"
ttable.0.0 0
ttable.1.0 0
ttable.0.1 1
ttable.1.1 1
}

ctl.dmixer {
type hw
card 0
}

[TKaluza]

This would really be great to have a system using more "mono" speaker to play in multiple rooms. I would also appreciate it!

[mr-manuel]

I have the same problem. My /etc/asound.conf looks like this:

ctl.!default {
    type hw
    card 0
}

pcm.hifiberry {
    type hw
    card 0
    device 0
}

pcm.hifimix {
    type dmix
    ipc_key 1024
    ipc_perm 0666
    slave {
        pcm "hw:0,0"
        format S24_LE
        rate 48000
        channels 2
        buffer_size 4096
        period_size 1024
    }
    bindings {
        0 0
        1 1
    }
}

# Left room (mono)
pcm.speaker_left {
    type plug
    slave.pcm "hifimix"
    # output = (left * 0.5) + (right * 0.5) = 0.5 + 0.5 = 1.0
    ttable.0.0 0.5
    ttable.1.0 0.5
}

# Right room (mono)
pcm.speaker_right {
    type plug
    slave.pcm "hifimix"
    # output = (left * 0.5) + (right * 0.5) = 0.5 + 0.5 = 1.0
    ttable.0.1 0.5
    ttable.1.1 0.5
}

# Both rooms stereo
pcm.speaker_all {
    type plug
    slave.pcm "hifimix"
    ttable.0.0 1
    ttable.1.1 1
}

pcm.!default {
    type plug
    slave.pcm "hifimix"
}

Would be nice, if you can support ALSA devices of the plug type or maybe you go a step further and let the user tell the Sendspin client to create a client per channel or a client per two channels.

Examples:

• Raspberry Pi with HiFiBerry AMP hat: left channel is for the first room, right channel is for the second room
• Small factor PC with surround soundcard, e.g. 5.1: Each channel is for a different room, or each stereo pair is for a different room

Currently in such setups Sendspin is not usable, so I have to stick with Squeezelite.

[Kreinoee]

I also battled with this recently without luck. I think it would be worth considering actually having sendspin-cli support this, so that you don't have to play around with an advanced alsa config to get it to work. It would also have the benifit of not needing to set up 2 concurrently running instances of the sendspin-cli.

[balloob]

Please try 5.8.0

[rvk]

With Sendspin 5.9.0 and MA 2.8.1 both Sendspin clients are able to start as long as no music is playing. When starting playback and linking clients, slave throws:

ERROR:aiosendspin.client.client:Error in audio chunk callback <bound method AudioStreamHandler._on_audio_chunk of <sendspin.audio_connector.AudioStreamHandler object at 0x7f8d2bb770>>
Traceback (most recent call last):
File "/var/lib/sendspin-olohuone/.local/share/uv/tools/sendspin/lib/python3.13/site-packages/aiosendspin/client/client.py", line 876, in _handle_audio_chunk
callback(timestamp_us, payload, self._current_audio_format)
~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/var/lib/sendspin-olohuone/.local/share/uv/tools/sendspin/lib/python3.13/site-packages/sendspin/audio_connector.py", line 451, in _on_audio_chunk
raise RuntimeError("Audio worker is not running")
RuntimeError: Audio worker is not running

Then for as long as the other sendspin instance is running, the crashed instance is unable to start and throws:

Error: No output device matching 'olohuone'

When restarting both instances, both are again able to start.

So either one can be used to play music, but not simultaneously.