ffmpeg -i IN.mkv -metadata:s:v:0 title="mon super titre" -c:v copy -c:a copy -c:s OUT.mkv

:s:v:0 > :v = Video stream :0 = Use first video stream

ffmpeg -i IN.m4v -metadata title="mon super titre" -c:v copy -c:a copy -c:s copy OUT.m4v

ffmpeg -loglevel quiet -i IN.mov -codec copy -metadata title="mon super titre" OUT.mov

ffprobe -loglevel quiet -show_format out.mov | grep title
TAG:title=My title