Hi, this may be a real newbie question, but I know very little about how FCPX actually works despite fumbling through using it for simple video tasks for years. Here's my situation:
A friend and I record video game playthroughs for Youtube. I play the games while sharing my screen over Skype, and I capture the game footage and my audio together as a .mov file using Quicktime Player, while she records her audio as a separate .mp3 using audacity (which she then Dropboxes to me).
Traditionally, I then drop the .mov into an empty FCPX project, and drag her .mp3 underneath it. This gives me two clips: my combined video/audio above, and her audio track below it. I find the audio spike at the beginning of both clips where we did a sync clap at the start of the recording, drag her audio into the right position so they sync up, do a little simple editing, and export it. Everything's gravy, no problems, this has worked for years.
Except, just recently, and with no change to either of our setups that we can figure out, this has stopped working -- her audio track is coming in several seconds short (over 30-40 minutes total duration). We verified this by doing a second clap at the end of of our most recent recording session -- with the claps at the front synced up, her clap at the end comes two and a half seconds early, and her audio drifts out of sync over the course of the video.
I told her what the actual length of her audio track ought to be, and she verified that, in Audacity, it is the correct length. It appears that the import into FCPX is where it's getting compressed/shortened.
Can anyone please tell me what has happened, and how do I fix this?