There is a video on the Canola2 site that shows someone picking media directories. I would say that if you make a folder on your card that is for audio, one for video, one for pics, that you can then specify only those directories per each type of media. If you leave everything loose in one directory, including other files, then Canola is always crawling through everything.

In Canola, when telling it where to look for video, you have the ability to do two things: drill open (or closed) directories, and to mark them for crawling. So drill away, but only mark the folders for content that you need to.