HEVC (H.265) files go black in viewer and timeline.

Help me, please. My 4k files from Mavic 2 pro h.265 codec go black in viewer and timeline after some time of editing. Any other video files look without any problem. If I transcode h.265 to proxy or optimize format, it looks good too. When I restart my MacBook Pro and do reset Nvram, original hevc files look fine but not for a long period of time. I did fresh installation of my Catalina, delete library files and reinstall Final Cut Pro 10.4.8 but I have the same problem. When I worked in Final Cut Pro 10.4.6, I had crashed os at all. This hevc files are on ssd hard disk.
My MacBook Pro is 2017. Catalina 10.15.5

Buk wrote: ...When I worked in Final Cut Pro 10.4.6, I had crashed os at all...

Could you please re-state and clarify this?

There is an FCPX bug in handling some types of HEVC files which began with 10.4.7 on either Mojave or Catalina. We don't have an exhaustive list of what works and what fails. The 8-bit 4k HEVC files from a DJI Inspire 2 will definitely fail. I don't know about the newer DJI HEVC formats.

The failure is typically an FCPX hang or crash during playback and skimming, but also when transcoding to proxy or optimized media. In October 2019 I forwarded this info to Apple Pro Apps Support, along with all files needed to reproduce the problem.

In your case if it works after transcoding to optimized media, just use that. If you use proxies it will still have to read the original files for the final output and a problem might happen then.

Another solution is externally transcoding before import using Handbrake or other tools.

Thank you for answer.
My files are HEVC 10-bit, 3840x2160.

I worked with proxy. However when I switch to original files before exporting I get black screen. FCPX export with these black screen. Than I reset Nvram and FCPX does export correctly. But sometimes I get problem during export too.

Your wrote to do externally transcoding before import using Handbrake or other tools. But what about quality? Do my quality change or no of I should be make transcoding? For these file I have special luts.

Do you think there is problem with Dji's file format, not with my MacBook Pro or Catalina? Maybe It would be right to send letter to Dji support, what do think?

If it did not crash, hang or show black screens using the same DJI 4k HEVC media on FCPX 10.4.6 but does on 10.4.8, that could imply the known HEVC issue.

It works OK with many HEVC codecs including the iPhone but it consistently has problems on DJI 4k 8-bit HEVC and 4k 8-bit HEVC from an Arlo security camera. There was another report of it crashing on 4k 10-bit HEVC from a Panasonic EVA-1, but that user never followed up.

The problem with proxies is you must go back to orig. media for the final export, so it can happen there. As a test can you transcode within FCPX some clips to optimized media and use only those clips in a test timeline, then try exporting that? If the transcode completes OK it thereafter never looks at the original media so should not have problems.

If that works it's the best solution because it avoids external transcoding.

If it does not work you'll have to externally transcode, maybe using Handbrake from HEVC to ProRes or the free version of DaVinci Resolve or EditReady2. I'm not sure the free version of Resolve has HEVC encoding due to licensing issues but you can check.

EditReady2 is an excellent utility, high quality and frequently updated. It is not very expensive: www.divergentmedia.com/editready

In general there should not be a quality problem because the HEVC source media must at some point be transcoded to ProRes cache files, then again to the final output codec. If you externally transcode to ProRes then import, it doesn't really add generational loss.