what does this mean? is there 1 video broken into several 'chapters' with blank footage in between each 'chapter"
and then what? is the video playing in a component? stopped in a player? does a button press call playing a random 'chapter' ? does it stop after that or coninue playing the video?
IF that is what you want, you would do best to embed cuepoints into your video - navigation cuepoints at the beginning of each 'chapter' and event cuepoints at the beginning or end of the blank footage if necessary.
write a function to call a random number which would relate to the number of chapters ( which would be placed in an Array ) and would navigate to and play that chapter. if you wanted it to end at the beginning or end of the blank footage, the player also needs to read that when it reached the next event cuepoint, it would stop.
you didn't give much to go on, but if that is what you are trying to accomplish, then this is one of the ways to accomplish it. without more info it is hard to offer more advice. but if that is what you want, and you need help doing it, just ask - but more specific questions will be easier to answer