Rotate video with ffmpeg
I often record family videos using my mobile phone and quite often the movie needs to be rotated 90 degrees. With a good build of ffmpeg it is a breeze:
ffmpeg -i input.mp4 -vf "transpose=1" -acodec libmp3lame -async 1 -vcodec libx264 -preset veryslow -tune film -crf 30 output.avi
This not only rotates the movie, it also recodes it in X.264 in a way that our TV can handle. Personally I can see no degradation in quality and the new file is much smaller.