After reading about how to convert a video by 90 degrees
I tried these commands:
mencoder old.mp4 -oac lavc -ovc x264 vcodec=mpeg4 -vf flip,mirror -o new.mp4 mencoder old.mp4 -oac lavc -ovc x264 vcodec=mpeg4 -vf rotate=2 -o new.mp4 ffmpeg -i old.mp4 -vf "hflip" -strict -2 new.mp4
but the converted video is still upside down.
Running the video with
mplayer -vf flip,mirror old.mp4
renders it as desired. But anyway, I'd like to convert it.
ffmpeg version 2.8.15-0ubuntu0.16.04.1 and
MEncoder 1.2.1 (Debian), built with gcc-5.3.1