I must confess, I didn't read the original post, just the title and whatever post was visible when loaded on n900 earlier. endsormeans may have a point, could have been used to advertise a product. I'm gonna have a guess that most of us have ffmpeg on our device from using other packages (cutetube for example).

ffmpeg -i input.mp4 -c copy -metadata:s:v:0 rotate=90 output.mp4

should be all that needed. No transcoding, just copy tracks into new file and add rotation via metadata. Whether it would be played back correctly on our device I can't be bothered to test at the moment.