I've been following the example here:
http://home5.inet.tele.dk/nyboe/flash/mediaplayer4/JW_API_xmpl_5-2-4-0.html#
And it seems to work with versions 4.2 and 4.3, but when I switch to 4.4, I get "No valid filetypes found in this playlist." The only difference between my tests is changing the player.swf version files.
Is there a different variable or additional variable I need to add for 4.4 to work?

If your file URI ends in a recognized media file extension, you don't need the type flashvar.
With the v4.4.x players, using type when there is a recognized media file extension seems to break things.
So, remove this from each track:
type:"video"Be sure that you remove the comma from the preceding line so the array is valid.