Originally Posted by
Weston@HPTuners
The video decoders are provided and managed by the operating system, so the most likely explanation is that the change in OS somehow lost the ability to decode the .MOV's from your JVC camera, at least in respect to the AVFoundation framework that RaceRender and many other modern Mac programs use. If there were additional codecs or other media technology installed on your system to help with your camera's .MOV format, that might not have remained operational after your OS upgrade.
QuickTime Player for Mac has additional capabilities that are generally not available for modern 64-bit software to use, so that's why it may be able to play or convert difficult video files that wont work in RaceRender or certain other software.