Suppose you are editing your video in Final Cut Pro X and you are pretty ahead in your workflow. You have already placed the background (bed) music along the video and have properly key-framed it around the dialogs.
Then, while reviewing the almost finished version, you realize that a piece of music does not really fit with the context. It definitely needs to be replaced, but doing so you will be losing all your key-framing work on that part. What a waste of time! But wait. Here is a trick that can help you.
It is actually possible to copy audio key-frames from one audio clip to another and here is how to do it.
Position the new audio background on the timeline, so it lays parallel to the one you intend to replace and they start at exactly the same time (you can use the snap functionality of the timeline to align them perfectly). At this point the new audio clip will be not key-framed. Select the already key-framed audio clip and do Edit –> Copy (or Cmd-C on the Mac).
Click on the new audio clip and do Edit –> Paste Effects (or Opt-Cmd-V on the Mac).
Voila! The audio key-frames have been copied to the new audio clip. You can now remove the old one or simply disable it to see the effect.
Hope you enjoyed this trick!