Yes, my first thought was to post it, but I watched it first and was disappointed, nothing like a test I'd expect from Paul.
He only tested two high-velocity ammos in the 1200-1300fps region (in his defence he rarely shoots any subsonic ammo at all), and the Stinger, (then declares the results apply to "most ammunitions"), only in semi-auto rifles (tends to reduce velocities already), with barrels from 16.5" to 22", so essentially minor variations on a single design - hardly definitive. It's the ammunition that determines the velocity in any given rimfire barrel, not the rifle.
I suspect that enough people will point this out to him, requiring a "Part Two"
It was good in that he agrees that barrel length is largely irrelevant to performance when choosing your rifle though. Even if getting up to 25" or more does cost you some velocity, or add some velocity, how well you can shoot with that rifle is way more important than the velocity.
Other than a very rudimentary two 4" 10rd groups offhand at 50 yards with two different rifles using the same ammo he didn't really venture into whether barrel length may have any benefit on accuracy. These are terrible groups compared to what Paul can shoot offhand with his peep-sight 10/22 so these are more likely a mismatch of ammo and rifle than an indication of anything the barrel length might cause.
If you want to hunt with subsonic ammo use a shorter barrel to retain as much velocity as you can, in a longer barrel the velocity may drop enough that at your hunting distances the bullets may no longer deform. If you want to use really high-velocity stuff use a longer barrel, in a 16"-18" barrel the Stingers, Copper-22 and Yellow Jackets might not make any more velocity than much cheaper high-velocity ammo.