Other very useful tip I picked up when doing video manipulation the other day that deserves its own post is reencoding any video so that it will work on a vanilla Windows Media Player (without any other codecs added). Windows Media Player is usually distributed with a very limited set of codecs, and unfortunately if you produce a video for the general public to view, you need to make sure WMP is happy to play it.
The tool for such a job is obviously
ffmpeg, but the suggested commands on the compatibility page of their site seem to compress the videos to a horrendous state at the same time, so after asking on their IRC channel on freenode this is the command that turned up:
$ ffmpeg -i input -acodec libmp3lame -ab 128k -vcodec msmpeg4v2 -qscale 3 output.avi
Wonderful. Now I can render to whatever I please and worry about compatibility later.