The video file works in every other piece of video software I have; after effects, fcp 7, Premiere and even compressor, just not fcpx, so I’m not having that there’s something wrong with the file (I’m a very stubborn chap). I thought there might be something up with my import settings, but it’s obviously just another bug in fcpx.
Anyways, I re-exported it as a prores 4444 and it works now, so at least it’s sorted. I’m just beginning to really hate how temperamental this piece of software is.