I think that if these handlers are registered only on the videoControls element, then you may not need to worry about the possibility of more than one touch.  If the user puts two fingers down on the controls and drags with finger one and then lifts finger two, it will probably be okay.  If they use two fingers where one finger is required, they shouldn't be surprised if things don't work quite right.

I don't feel strongly about this, but I prefer simpler handlers that aren't state dependent, so they can't break if the state isn't set correctly.