Originally Posted by VGeorgie

Most people get this wrong and keep using the main or baseline profile, which for HD will suck up so much CPU anyone with a marginal PC (Pentium III, G4 Mac, etc.) won't be able to view the video without problems. Be sure to select High Profile.

Same as when encoding FLVs using VP6 codec, you'd pick VP6-S. S means standard but in a twist of logic, that's the one for HD. The (E)nhanced profile is for standard def.