Playing video files over Jitsi

[bruce.nikkel at bfh.ch]

Hi Everybody,

I teach some modules at BFH and play a lot of video files in one class.
Now that we are teaching online (again), I needed a quick hack to play
the video files in reasonable quality over Jitsi to the students (I know
Jitsi can stream from YT, but I don't want that).

Just in case somebody else needs it for teaching or presentations, I
made a little diagram and some tips to explain how I set up the audio
and video loopback to play local video files directly from a Jitsi
client on Linux.

This might work with Zoom and Teams, but I didn't test it. 

Regards,
Bruce Nikkel

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Basically two kernel modules create fake/virtual microphone and webcam devices that jitsi can use. Then ffmpeg plays the video file into to these devices.

Make sure you have the right video device (/dev/video#) created by the v4l2loopback kernel module. Usually its the highest number.

The "exclusive_caps=1" is needed to fool jitsi/chrome to think they have exclusive control (otherwise they may not use the device)

The "hw:VirtualMic,1" might be a different number than one, if you get related errors try changing that to 0 or another number linked to the snd-aloop module.

If you can, install the latest v4l2loopback from the github (https://github.com/umlaeute/v4l2loopback)  This is v4l2loopback-dkms-git on Arch Linux.

# the camera only appears in jitsi when a video is playing. You have to play that manually in a separate shell:
$ ffmpeg -re -i vid.mp4 -f alsa hw:VirtualMic,1 -f v4l2 /dev/video2

If you have problems playing some video file formats or codecs, try adding these additional ffmpeg flags:

# blank video screen or trouble decoding ?
 -f rawvideo

# error message "cannot set channel count to 1 (Invalid argument)" ?
 -ac 2

# error message "sample rate 48000 not available, nearest is 44100" ?
 -ar 44100