I have a habit of recording with my camera tilted by 90 degrees which on my camera does not register when its saving the file so I end up with a video not meant for someone with vertigo. The solution, which is decently simple once you find it, is to run the command
mencoder -ovc lavc -vf rotate=1 -oac copy input.AVI -o output.AVI
The rotate=1 can be replaced with whatever you want. Alternatives include:
0 Rotate by 90 degrees clockwise and flip (default).
1 Rotate by 90 degrees clockwise.
2 Rotate by 90 degrees counterclockwise.
3 Rotate by 90 degrees counterclockwise and flip.