To playback video in mplayer in different sizes, just use this command:
mplayer -vf scale=960:720 my.avi
This will scale up a small frame size video to a higher size. This is good if you are playing video on the framebuffer console with mplayer and you want to be able to see the video in a larger size. Just add your user to the video group in the /etc/group file to be able to play video on the virtual consoles.
mplayer -vf scale=960:720 my.avi -flip
This will play the video upside down. Cool trick to show people.