v4l2.md

Video4Linux

On Linux, it is possible to send the video stream to a v4l2 loopback device, so that the Android device can be opened like a webcam by any v4l2-capable tool.

The module v4l2loopback must be installed:

sudo apt install v4l2loopback-dkms

To create a v4l2 device:

sudo modprobe v4l2loopback

This will create a new video device in /dev/videoN, where N is an integer (more options are available to create several devices or devices with specific IDs).

If you encounter problems detecting your device with Chrome/WebRTC, you can try exclusive_caps mode:

sudo modprobe v4l2loopback exclusive_caps=1

To list the enabled devices:

# requires v4l-utils package
v4l2-ctl --list-devices

# simple but might be sufficient
ls /dev/video*

To start scrcpy using a v4l2 sink:

scrcpy --v4l2-sink=/dev/videoN
scrcpy --v4l2-sink=/dev/videoN --no-video-playback  # disable playback window

(replace N with the device ID, check with ls /dev/video*)

Once enabled, you can open your video stream with a v4l2-capable tool:

ffplay -i /dev/videoN
vlc v4l2:///dev/videoN   # VLC might add some buffering delay

For example, you could capture the video within OBS or within your video conference tool.

Buffering

By default, there is no video buffering, to get the lowest possible latency.

As for the video display, it is possible to add buffering to delay the v4l2 stream:

scrcpy --v4l2-buffer=300     # add 300ms buffering for v4l2 sink