It also relies on Quicktime 7 (for h.264), which I am sure will be released concurrently with 10.4.
There is some noise being made at the moment about the fact that Quicktime 6 pro users will have to buy a new licence for Quicktime 7 Pro if they upgrade to Tiger. Second hand from macfixit :
"As noted by MacFixIt reader Scott Mahrer, QuickTime Pro 6 users who upgrade to Mac OS X 10.4 (Tiger) will not be able to use their current license codes for the newly included QuickTime Pro 7. - I did verify with Apple's techs today that a Quicktime Pro version 6 key will not work with Tiger and Quicktime 7! Furthermore, the Apple Store does not know when Quicktime Pro 7 will be available, or how much it will cost to upgrade!"
Just something to keep in mind if you rely on Quicktime Pro. cheers Jude
