Using Droidcam on Linux with V4L2

# Possibly optional steps that improve resolution.
# These must be done as `root`.
# Source: https://www.dev47apps.com/droidcam/linux/
rmmod v4l2loopback-dc
insmod /lib/modules/`uname -r`/video/v4l2loopback-dc.ko width=1920 height=1080

# Open DroidCam(X) on Android device. Start it up. Get IP address and port.
# In this example, the IP address is 192.168.1.39 and the port is 4747.

# Put this in one shell to create a /dev/videoN node that other programs can connect to.
# (I did this as `root`, but I'm not sure if `root` is needed.)
droidcam-cli -a -v 192.168.1.39 4747
#```
#Client v2.0.0
#Video: /dev/video0
#Audio: hw:3,1,0
#```

# Alternatively, if the device has ADB debugging over USB enabled
# in its developer options, then droidcam-cli can connect this way
# over a USB3.0 wire:
droidcam-cli -a -v adb 4747

# This connection seems to have MUCH better bandwidth/framerate!
#
# If connecting from a new computer, the phone might get a prompt
# asking whether the computer should be trusted. This prompt must
# be answered affirmatively before the above `adb` mode will work.
# After answering the prompt, it may also be necessary to restart
# the DroidCam(X) app on the phone/device, and possibly also
# necessary to restart `droidcam-cli` with the same command above.
# If all is good, it will give the same output as the IP version.

# It should now be possible to use the "webcam" from other programs, and from web apps like Discord.
# (This should be done as the user in the desktop environment, NOT as root.)
# To test functionality manual, `mpv` can be used like so:
mpv av://v4l2:/dev/video0 --profile=low-latency --untimed
#```
# (+) Video --vid=1 (rawvideo 1920x1080 30.000fps)
#VO: [gpu] 1920x1080 yuv420p
#V: 02:08:20 / 02:08:20 (100%)
#```
# NOTE that the `/dev/video0` in this command must match the "Video:" field from droidcam-cli.
# It just happened to be `/dev/video0` in this example, but it could be any `/dev/videoN` node.