I saw video output (which looks like headphone output) on my Canon EOS 450D.
What is it for? Is it possible to record video through this output?
The 450D does not support video recording, but you can use the video out to display images on an external TV. You could use the live view mode of the camera to generate a live video signal, but you would need to encode this in some form yourself (as well as syncing with audio)