This, which does not require post-capture transcoding. One of its strong features is being able to save out a very high quality result in Apple ProRes 422 if you don't mind a huge file. I didn't do that on this capture, though, since I was expecting to go on for hours and hours... until I got too drunk to focus and had to go take a nap. ; )
https://www.shinywhitebox.com/#ishowu-hd-pro
One caveat to it is that, because it connects to the video system at an optimal point, yielding incredibly smooth captures, doing so eliminates its ability to capture copy-protected content. For that, you can use SnapzProX, which I also have but rarely use these days because it takes so long to prepare the finished capture.
The Game Capture HD doesn't record desktop footage (unless you sent the signal from your computer out to the Elgato, then into a tv, and then back into the computer to be captured by the Elgato software, but that's a real pain in the ass and it doesn't work very well). Sony Vegas is really good, but it is a bit pricey. You could get the Creative Cloud from Adobe, and get access to their extensive library of software, all of which is really good. The Blue Snowball is a really good mic, there's nothing you need to worry about with it. Just make sure you use headphones, you don't want the mic to pick up the sounds coming from the tv. Also, the Elgato comes with a very basic video editor. You can trim videos, give them titles, and a few other things. If you want to record your screen, and your on a Mac, you may want to consider Snapz Pro X.
Hopefully someone has a better answer but I'll tell you what I know in case nobody else answers.
It's gonna be a goddamn mess. You'll have to find a way to download the media file, be it FLV, MP4 h.264, or WebM, and then convert it to a format Mac PowerPoint feels comfortable with since it's using the system QuickTime. (the MP4 file would be fine on its own and the FLV could probably be re-containered but the WebM is no good).
It is sort-of possible to do this with the page source alone, but the youtube page source is awfully complicated at least to me, even with assistive tools.
PowerPoint used to be ridiculously finnicky about video but I haven't used the latest version.
If you're doing this a lot and you have a Mac that's not very old, it might be easiest to just re-record the screen using something like:
http://www.ambrosiasw.com/utilities/snapzprox/
also /r/applehelp/ is an active support subreddit
Snapz Pro is pretty awesome
http://www.ambrosiasw.com/utilities/snapzprox/
A bit pricey but they also have a free trial that you check out before paying the hefty 69 bucks for the software, but well worth it!