If you want to record with HD resolution then choose "Another game with full screen" at video devices menu and select resolution which you are going to run.
The bigger monitor/TV - the better will be experience. So, you can light up a cigarette and watch your favorite replays now in HD.
You can also use HD for usual gameplay but personally I don't think that's a good idea if you wanna play ladder games.
Credits to mca64launcher - long live maker of this awesome little packed program. And also big cheers for maker of resolution hack - hellinsect.
Replay: Silent Control (Red T12) vs XellOS (Blue T2)
Date/Event: WCG 2005
Map: (2) Paranoid Android