Flipping webcam image with FFmpeg

2022-01-30

Install

ffmpeg https://ffmpeg.org/
v4l2loopback https://github.com/umlaeute/v4l2loopback
v4l-utils https://github.com/gjasny/v4l-utils

Load v4l2loopback module

# modprobe v4l2loopback devices=1 video_nr=10 card_label="Loopback Camera" exclusive_caps=1

devices=1 - create one device
video_nr=10 - choose device id, the path will be /dev/video10
card_label=“Loopback Camera” - choose name
exclusive_caps=1 - reports CAPTURE/OUTPUT capabilities exclusively (applications couldn’t see my device without this option)
See if you can see your new device:

$ v4l2-ctl --list-devices 
Loopback Camera (platform:v4l2loopback-000):
	/dev/video10

Run ffmpeg

$ ffmpeg -f v4l2 -i /dev/video4 -vf "vflip,format=yuv420p" /dev/video10

-f v4l2 - input format
-i /dev/video4 - input device (your webcamera)
-vf “vflip,format=yuv420p” - flip it! and set pixel format
-f v4l2 - output format
/dev/video10 - output device
In an application select your new “Loopback Camera” device.