This python script allows you to provide v4l2loopback, or other applications, with frames from a DSLR. Unlike other options, this script allows you to send commands to your camera while capturing preview frames. This lets you, for example, adjust the ISO and control focus.
For windows to work you have to install libgphoto2 using msys2. Then replace the driver with Win-USB using Zadig (I have tested this with my D5600 and without it, you won't be able to access the camera.)
To play with mpv --demuxer-lavf-probescore=10 must be used since the stream has no timestamps.
For low latency add --no-cache --untimed --demuxer-thread=no --vd-lavc-threads=1 --no-audio
--demuxer-thread=no must be used otherwise mpv will be buffering a lot, and the output will be choppy.
This can use a lot of CPU without hardware decoding. On my i7 9700k on Windows 10, it hits 25% utilization sometimes.
Example
mpv --no-cache --untimed --no-demuxer-thread --vd-lavc-threads=1 --demuxer-lavf-probescore=10 --no-border --no-audio udp://127.0.0.1:8833
For mpv to do hardware decoding add --hwdec-codecs=mjpeg
This may or may not cause issues for you.
On my i7 9700k on Windows 10 with an RTX 2080 SUPER it significantly reduces CPU usage with little noticeable latency.