Tascam US122L, JACK, PulseAudio and OBS

[stephematician]

Apologies if this is the wrong place - however I'm getting an error most of the time in a very specific situation.

My setup is a TASCAM US122L USB interface, which ALSA is capable of recognising and setting up as a usb_stream device. I then run jackd for this device, load the pulseaudio module for a JACK source (at this point I can record via parecord), and then attempt to add a PulseAudio source to OBS.

The contents of my .asoundrc are somewhat widely used:

# The usb_stream plugin configuration

pcm.!usb_stream {
        @args [ CARD ]
        @args.CARD {
                type string
                default "1"
        }

        type usb_stream

        card $CARD
}

ctl.!usb_stream {
        @args [ CARD ]
        @args.CARD {
                type string
                default "1"
        }

        type hw

        card $CARD
}

I run jackd with a command like:

/usr/bin/jackd -v -p128 -dalsa -dusb_stream:CARD=US122L -r44100 -p256 -n2 -C

I then set up a source in PulseAudio using pacmd load-module module-jack-source. Typically at this point, parecord --device=jack_in test.wav records no problems.

Then I'll run OBS and try to add a PulseAudio input, at which point I usually get a very short period of input (less than 1 second?) and then the input will cut out and I'll see the following error in jackd output:

Couldn't configure usb_stream
: Input/output error
ALSA: prepare error for capture on "usb_stream:CARD=US122L" (Input/output error)

Upon tracking this down, it seems that some call to snd_pcm_prepare by JACK is receiving an error code; but I'm not an expert in this library (or alsa) so it's hard for me to even guess what the problem could be.

It could also be a problem with ALSA so I shall also raise this issue there.

What's extra strange is that twice I have got the PulseAudio input to work in OBS and it hasn't crashed, but I cannot determine under what circumstances it worked and why it worked. Most of the time, it fails as described.

[stephematician]

May be related to this bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1960703