What is the data-rate of your movie?
(apple+i in quicktime)
What OS?
What MacPro Hardware spec?

As has been said a million times here:
Catalyst is not quicktime
just because a file plays in Quicktime, doesn't mean it will play in Catalyst

Quicktime Player prioritise audio - to prevent glitching.
Catalyst prioritises video - different to Quicktime Player - to provide best playback

However, if using an audio playmode, then Catalyst prioritises audio to ensure that you don't hear any audio dropout.
But this can be very processor intensive, especially for a PhotoJpeg file of that resolution.

If using 10.8.5, then render file as ProRes LT or Proxy and see how that works (data rate may still be too high)

If you still get issues, then render the audio as a separate 16x16 black file.
Run the audio file on a separate layer and sync the video playback to the audio layer (using sync ID playmode)

This means that the video layer will be rendered by the graphics card and the audio by the processor

Depending on the data rate of your movie file, you may need to reduce the quality or resolution until catalyst can playback smoothly...

S