Thanks for recording yourself, it's a really valuable means of feedback.
Master difficulty is downright silly, I saw him do some stuff in your video even I didn't know he could do. Good job beating him.
The window for blocking is quite wide but it can be tricky recognizing each attack in time to react to it, especially using keyboard controls. I'm thinking of adding a 'game speed' option so new players don't get thrown in the deep end.