In FCPX I can select a video and audio clip and do "Synchronize Clips" using the "Use audio for synchronization" option.
Now I have a new clip in the browser on which I can say "Open Clip" and then see the timeline with the audio synced to the video.
If I want to add another audio track into this synced clip, I want a way for the additional audio to be automatically synced too.
I can't seem to find a way to do this - is it even possible?