What CODEC is used in the QuickTime files?
Open the file n Quicktime: Window > Show Movie Inspector, the CODEC is shown against: Format
You can also repair Keynote using this, ensure you complete all the tasks and in the order shown:
delete all the iWork applications if you have them, not just Keynote, using Appcleaner from Mac Update, its a freeware application
empty the trash: Finder > Empty Trash
Shut down your Mac, wait 30 seconds, then power on the Mac, immediately after the start chime, hold down the Shift key
When you see the grey Apple symbol and progress indicator (a spinning gear), release the Shift key.
If you are prompted to log in, type your password, then hold down the Shift key again as you click Log in.
Let the Mac fully boot up, it will take longer as the OS is repairing the drive
when fully booted, go to Applications > Utilities > Disc Utility; click on the boot drive then First Aid tab and click repair disc permissions
when complete, restart the Mac normally, Apple menu > Restart
install Keynote from the Mac App Store