bmusb-v4l2proxy is not documented upstream, beyond this comment in v4l2proxy.cpp,
which may prove useful:

// A helper proxy to send data from bmusb to a V4L2 output.
// To get it as a V4L2 _input_, you can use v4l2loopback:
//
//   sudo apt install v4l2loopback-dkms v4l2loopback-utils
//   sudo modprobe v4l2loopback video_nr=2 card_label='Intensity Shuttle (bmusb)' max_width=1280 max_height=720 exclusive_caps=1
//   ./bmusb-v4l2proxy /dev/video2
//
// There is currently no audio support.

As with bmusb in general, running as a user that is granted permission
to run at realtime priority can be useful. This can typically be set up
in /etc/security/limits.conf (followed by a re-login).

Debian does not automatically start up bmusb-v4l2proxy for you; if you
wish for that to happen, you need to add a separate systemd service,
udev rule or similar.
