I’ve googled a lot for a solution, but without any luck. They played fine without any sound issues using preview and also in QuickTime Player, but once imported to the latest iMovie 10.1.8, the MP4 clips lose sound in the middle. “I have several MP4 videos downloaded from Facebook. MP4 video clips have no sound in iMovie 10.1.8 on High Sierra Here we explain a solution to solve MP4 audio lost issue while loading into iMovie 10.1.8. This is probably a system issue or an audio codec issue. There’s no sound after imported MP4 video clips into iMovie 10.1.8 on High Sierra? Actually, the same issue has been reported while importing MTS video into iMovie 10.1.8 after updated to macOS High Sierra. I now have version FCPX 10.4.6 and it's running beautifully on High Sierra.This entry was posted in Encode MP4 to QuickTime Video file conversion on by Richard Clicked on it, installation began and completed. FCPX came up in the search choices and this time, Instead of 'upgrade', it now said 'install'. I then went back to the App store and this time searched for 'Final Cut Pro X' in the search window (I did NOT go back to my Updates window.). My solution: I went into my apps folder, took FCPX and moved it to the trash. When I went to update my FCPX tonight (It's been at 10.2.1 for sooo long), I got the same message 'Incompatible Update.' The App Store was forcing me to upgrade to version 10.5.1, which would of course require me to also upgrade my OS to Mojave. I've been upgrading my old mid-2010 Mac Pro (new metal/RX580 GPU, amongst other things), and got it to High Sierra where I would like this machine to stay so that I can continue to also use CS6 for my photography work. I know this question was from a year ago and it's likely been resolved by the poster, one way or another, but I had the same situation and found a super simple solution that worked for me.

Otherwise, follow Tom's advice If you can. I'm still on HS but now considering upgrading to Mojave mainly for the latest version of FCPX. I know it exists and I used to have the direct link, but access may be tied to Mac and Apple ID. If not, call Apple support and they may direct you to the appropriate download. From there, Apple does have FCPX10.4.6 (last version to work on High Sierra) on their servers and it may direct you to the proper version in App Store. Link in support document to older trial version. I believe that this page is still active and will allow you to download FCPX 10.2.3 free trial, not current version. I'm rocking on a 2012 rMBP and really want a new Mac, at least dreams are free. 10k $$$ should get you going well, but for me, not going to happen today. You are sporting a pretty old Mac, so performance will suffer, especially with high resolution media.

Install imovie on high sierra