Quicktime won't play HDV .mov
I upgraded to Lion, and noticed that Final Cut Pro was not playing my HDV .mov clips off of an external drive in the timeline.
Upon closer inspection, Quicktime also couldn't play these HDV clips either. Quicktime X said "The document ... could not be opened. This media may be damaged." Quicktime Player 7 (Pro) says "The movie could not be opened. An invalid public movie atom was found in the movie."
I then take this same external drive to a Snow Leopard installation, with FCP on it, and all clips work fine, and can be opened in both Quicktime X and Quicktime Player 7 (Pro).
I can also open these files in VLC in Lion without an issue, so it seems that maybe it's a Quicktime codec issue. I look in /Library/Quicktime/ and the AppleHDVCodec.component is there.