I just rewatched the video...
For a headgasket leak... (But I doubt you have one
A leakdown and a compression test are helpful for testing for HG leaks. They are usually visible and you can smell the coolant cooking (in subarus). Check for air bubbles in the radiator fill point as well. Heavy white smoke from the exhaust is usually a definate. An air hose is really all you need to confirm it though.
I hate to be the bearer of bad news, but that is the noisest subaru valve-train I have heard in a while. That's pretty bad considering how far out of spec they are from the factory (I have seen +/- .2+). Did a reputable shop do the work?
Here is what I would do if I was you. Your valves are extremly loud, and the clearances are off enough to cause big problems later on.
Start by removing your timing belt. It almost sounds like your belt may have jumped a tooth too. Pop off the valve covers, and measure each individual clearance. Compare the exact measurement to what subaru requires. Also look for consistancy between each corresponding cylinder. I have seen measurements be off, but equally-off on each cylinder and the engine would run prefect. It might be something as stupid and re-arranging buckets, but you have to take things back apart to make sure. Triple check your timing belt when you go to reinstall. I have had times in the past where I was setting the timing, and would go to answer my cell and overlook the stupidest things