virtual_oss how do you record currently playing audio

Im a bit stumped on how to use virtual_oss to record audio that is currently over a particular dsp device
and was wondering if someone could me a prod in the right direction

i have loaded the cuse module

What id like to do is create a virtual audio device that can be recorded with ffmpeg

Heres the contents of /dev/sndstat

pcm0: <Cirrus Logic CS4206 (Internal Analog)> (play/rec)
pcm1: <Cirrus Logic CS4206 (Analog Headphones)> (play)
pcm2: <USB audio> (play) default
pcm3: <USB audio> (play)

The built in speakers are pcm0 and dsp0.1, which i can see can play and record
however my usb dac which is pcm2 and dsp2 can only play

Can i only capture audio from an interface that can both play and record, like dsp0.1 ?

I had a look at the handbooks example for virtual_oss and bluetooth

# virtual_oss -C 2 -c 2 -r 48000 -b 16 -s 768 -R /dev/null -P /dev/bluetooth/headphones -d dsp

and also found a bit of code om someones blog

# virtual_oss -S -C 2 -c 2 -r 44100 -b 16 -s 1024 -f /dev/dsp2 -d dsp -w dsp.rec.wav -l dsp.rec

the problem is if i use -d dsp with virtual_oss then programs like mpv and mpd then cant the dsp device to play audio through,
i see some people using -d vdsp with virtual_oss, see forum post below

in a nutshell what id like to be able to do is capture the audio that is playing out of the current dsp device and send it to a virtual audio device,
which i could then use with ffmpeg so i can record the desktop audio at the same time as recording the screen

I did come across some bits of code on the forum

I've been on a quest to figure out how to capture audio output for a long time. Apparently OSS doesn't natively support it. Recently I managed to kind of do it using audio/virtual_oss (specifically virtual_oss -C 2 -c 2 -r 48000 -b 16 -s 1024 -f /dev/null -w vdsp -l dsp), but with two inadequacies:

  1. It stops the audio from playing at the same time. Ideally I could use to be able to hear it and record it at the same time.
  2. I can't get OBS to detect the virtual device, so the audio output recording has to be done separately from audio input and video (causing difficulties with synchronization). I know OBS depends on pulseaudio to be able to detect any devices on FreeBSD.
So my question is how to solve these two remaining issues. If I can solve at least one of them, it might be enough to get me to do my video recording on FreeBSD instead of resorting to OBS on a Windows machine.

Put something instead of /dev/null there. -P /dev/dsp1 -R /dev/null, for example.