[FFmpeg-user] Stream a video with a watermark or image over it

[dj_def at webmail.it]

Of course, sudo is useless, I did a bad copy and paste as I was testing
it with sudo and took the shell code from there.
It is working with avi, even if my source is an mp4 file (the streaming
of an ipcamera). I think it depends on the type of the video source.