Why is playback of mp4 really laggy?

I'm been recording with my dslr and iphone 5s and all the videos play just fine in FCPX. But this week I imported some videos from my GoPro camera which records in mp4 format. It imports it fine, but the playback is really laggy. How do I fix this? Here's some info about the file. All the files from the GoPro behaves the same way it's not just this one file. Also I was able to play this file just fine in Quicktime but just laggy in FCPX.