You can use ffmpeg for this:
ffmpeg -t 7200 -s 640x480 -f rawvideo -pix_fmt rgb24 -r 25 -i /dev/zero empty.mpeg
UPDATE:
-t: length of the video (in H:m:s format 00:00:00 or in seconds 0.000)
-s: frame size
-f: video format
-pix_fmt: pixel format
-r: fps
-i: input