I can't import H.265 file into Final Cut Pro

I have done some research and some testing, and I think I have the solution for you.

Add this option to your ffmpeg command:

-tag:v hvc1

For example:

ffmpeg -i in.mp4 -c:v libx265 -c:a copy -tag:v hvc1 out.mp4

produces a file that plays in Quicktime and in FCP.

Without the -tag:v hvc1 option, Quicktime says that the file contains some media that isn't compatible. If I still hit Continue, it will open without video, and in the Movie Inspector it says "Video format: HEVC (Parameter Sets in Bitstream)"

(the parameters part is the problem)

You should be able to losslessly change the offending Codec ID hev1 to hvc1 which Big Sur 11.6 QuickTime and FCP 10.5.4 insist using:

ffmpeg -i input.mp4 -vcodec copy -acodec copy -tag:v hvc1 output.mp4

Below the original hev1 and the updated hvc1 HEVC .mp4 in FCP import dialog:

Invisor can nicely highlight differences between movie files when you drop a folder on it:

“but start by complaining then read it”

What does that mean? What happens? Can you give the specs of the MP4? Maybe the problem originates in there.

VLC has great capabilities as a player. It can play many things that professional editing applications don’t support.

What version and OS are you using? Is this a camera file? What are you doing to import and what happens when you do it?

FCP supports industry standard H.265. I don’t think lib265 is. VLC plays anything.

Does your file play in QuickTime?

You could use HandBrake to convert to H265.

Using either the videotoolbox or x265, the resulting video plays fine in Quicktime and in FCP.