If you download a flash movie from YouTube or Google videos - often it is convenient to convert it to mpeg format. On Linux and Windows (under Cygwin) this can be achieved using ffmpeg, for example:
ffmpeg -i input.flv -ab 56 -ar 22050 -b 500 -s 320x240 output.mpg
And if you want another format, simply change the file extension on your output file. So for mp4, for example, the command would be:
ffmpeg -i input.flv -ab 56 -ar 22050 -b 500 -s 320x240 output.mp4