First enable sentry/v4l2loopback repo for install the v4l2loopback
dnf copr enable sentry/v4l2loopback
then install v4l2loopback:
dnf install v4l2loopback
then run modprobe v4l2loopback for creating video device.
finally find your mp4 file and type this command for manipulating the webcam:
ffmpeg -re -i input.mp4 -map 0:v -f v4l2 /dev/video0
Screenshot:
