I am unable to upload a video to iMovie

Hello. I have tried uploading this iMovie project about 10 times now. It's a 30-minute video and there have been several reasons why it hasn't uploaded. At first, it was because the project media wasn't fully downloaded to imovie and was existing on the SD card. Then, I fixed that problem, redownloaded the media, and copy/pasted the project onto a new iMovie library. When I tried downloading it it would stop halfway through. I cleared preferences and copy/pasted the media into a new movie again. This happened a number of times. I shut off my laptop, reopened it, and tried again. Finally, it would get to the final part of the download and iMovie would "quit unexpectedly". So now, I've gotten it to a point where it will download it without that error but when I open it in files I get the message that quick play cannot read it. What can I do to fix this?

[Re-Titled by Moderator]