Canon 5D Mark4 - 4K Video Issue in FCPX

You have to create Proxy files AND you have to choose to use the proxy files. In the image attached I am using the original files. You may find that creating optimized files works for you but using optimized files will greatly increase the diskspace you use. If you need to view images in detail while yo work, optimized files may be helpful but Proxy files will probably work. The original compressed files require more horsepower from the computer than "unstuffed" images or proxy files but almost any kind of compressed file will work when you create proxy files.

Have you tried creating proxy files?

Also check if the Browser settings are set to Better Performance:

Al

I have a Canon 5D Mark IV and I have shot and edited several 4K videos with footage from this camera in FCP X. The MJPEG format is not a problem for FCP X and, in fact, is easy for the software to decode. However, the file sizes are enormous with many of my clips being tens and even hundreds of gigabytes in size. You need to have these clips on a fast raid system for FCP X to play them back smoothly. I store all my FCP X footage on a pair of Promise Pegaus 2 raid 5 arrays. My computer is a Late 2013 Mac Pro with a pair of D700 graphics cards and 65 GB of RAM.

Tom