If you're the only one who can see the vlog, it's legal (unless, say, the content comes from a DVD you stole from the store). If anyone else can get to it, it falls under fair use, and that's about as stable a concept as an elephant balancing on a non-existent pin. What's fair use to one judge is a definite copyright violation to another.
The general rule when it comes to IP copyright is "if in any doubt, don't". ("See the way X is pointing in this clip?" and 3 seconds of video is probably fine. 2 minutes of music or a speech may be stepping over the line.)