Sharing iMovie film to YouTube

That type of error message usually means that there is corruption in the project, in this case at the beginning of the movie. Expand out your timeline and scroll around the beginning of the project, looking for a black frame, white flashes, artifacts and any other signs of corruption. Cut out any that you find and try re-exporting. It might be a title that is causing the problem.

Also, try exporting your project to your desktop, and from there drag it into You Tube’s upload window, and follow Facebook’s procedures for uploading to its website.

— Rich

No telling what can cause corruption. Possibly the issue is related to the camera when the vids were taken, or maybe occurred during the rendering process, possibly due to a format issue.

Try converting your troublesome clips to H.264, Mp4/AAC with the free download, Handbrake. Do that even if the codec already is indicated to be Mp4/AAC. Re-rendering often cures the issue.

You can get Handbrake here:

https://handbrake.fr/

A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to complete. Then save and import the converted clip into iMovie. See if that solves it.

To address why the split function doesn't work, try deleting preferences. Open iMovie while holding down the Option

and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

-- Rich