To test the booster(and it's check valve), turn the engine off and pump the pedal, letting it reach the top of it's travel, a few times. It should, after a couple pumps, start to firm up. Eventually it will be very stiff/firm as there's no longer assist from the booster.
Next, apply moderate pressure to the brake pedal and start the engine. The pedal should sink a little as the booster begins to assist again.
To test the MC - normally only used to test if the MC is leaking internally, but it really tests the entire system from MC down to calipers - turn the engine off and pump the pedal until it's firm (no booster assist), then push down hard (within reason) on the brake pedal and hold it there. It shouldn't sink towards the floor if you hold it there for 15-30seconds. If it sinks significantly and hits the floor, you've got a serious leak, whether it's an internal MC leak or otherwise.
edit: Fwiw, I'm not an expert, but it did sound like the ABS pump was running at first in the video. Later on it sounded a bit different, hard to say. The fact that the sound got louder as you pushed it (you could hear it more muted before he got on the pedal) does seem to point towards it being the booster, though I've never dealt with or heard one that was failing.
Last edited by A-series; 01-11-2009 at 04:53 AM.