For an excellent source on slow-mo and high speed film of tennis pros in action go to:

VirtualTennisAcademy.com              TennisOne.com              Tennisplayer.net
Both are membership only sites and offer analysis of what the pro is doing and how they are doing it.  The films are great stuff, and the rest of it, as with any site including this one, caveat emptor.

For a FREE resource to look at pros on film check out the USTA's very own

Player Development Digital Video Library

and click on the link "USTA Coaching Education Digital Video Player Library" in the first sentence.