Streamclip Question

[jmak]

I'm making a demo reel of a dozen films I've made, have clearance for this. Took me some time to figure out Streamclip, sort of... I notice when I try to load some dvds that a box comes up and says "cannot read the beginning of this file", or "cannot read this file". Since these area all copyrighted, I wonder why some work and others don't? I use a ripper as well.