Well, think about it, how is a video that's stopped playing different than a flash ad? From a code standpoint? Both are pieces of flash programming embedded in a website. I would think a flash video playing would suck battery very roughly, meanwhile flash video paused/ended would suck battery ~ the same as a lightly-animated flash ad would. I honestly don't know, but to me it seems like it would work the same. The video might actually suck more power, if it's like most flash videos on websites nowadays, which have a little cycling menu of related videos for you to click on that pops up after the video plays.

BatteryGraph does show CPU activity. It's vague, and it's in purple bars, so it doesn't log WHAT was using the CPU, but it is something. Other than that, I suppose you could set up something to log the output of top, HTop, or some other process viewer.... *Shrug* Not my area of specialty.