[Chris27]

Just to be clear, a video container (e.g. mov, wmv, avi) is not the same as an encoding format (e.g. XVID, x264). You technically don't have to reencode the video when you extract the video source from one container and put it in another. It is perfectly valid to take, say an x264 video, from a container such as a .mov and place it in another container such as a .mp4. Since the video is not encoded (compressed) again, there is no quality loss.

Typically, different video and audio codecs are associated with different containers. If you choose a bizarre codec container combination, your video player may not correctly handle the file. You typically don't have to worry about this as most video encoding software will choose the codecs for you when you select the container type.

I can also vouch for handbrake (or at least the mac version)