In the first Video there aint really much to it which is what makes it so good - simplicity. You are also right - it looks to be simply chroma keying and Masking, but clever masking. The second one - (Big up Mr. Ron Size) is much the same. There is nothing much more to them than that.
As to resources - this is down to what you use to do them. Most Non Linear edit systems will have these features but they all work diffrently but with the same principal.
If you are using lets say premier you can simply Google the term "masking in Premier" and you will get 100's of relevant hits