ANSWER:

Removing com.apple.iPhoto.plist (in /Users/~/Library/Preferences), seems to have solved the problem.

Credit to the post by “Old Toad” -> https://discussions.apple.com/thread/2796168?start=0&tstart=0

Is there any public registry of the values? When I took a diff of the new and old values, I did not see anything obvious that was reset that would cripple video playback> (I assumed it was a stale preference or a new, bogus default value.)

by benc from http://superuser.com/questions/429248