Longer videos now play all the way through

The last release let the browser play video from its own code, but with a catch: to play a clip it had to hold the whole thing in memory as it went, so it only played the first half a minute and then stopped. That limit is gone. Video now plays a piece at a time, keeping only a small window of it in memory at once, so a clip of any length plays start to finish without using more and more memory the longer it runs. A three-minute video plays like a three-minute video should, and jumping back and forth in it still works.