Using iMovie I continuously get imported clips blacked out with message Missing Camera. Is this because some clips are too long

Hello laurencefromnewcastle,

From your post it appears that you are having an issue with some clips imported into iMovie.

When you check the files these clips are referencing, are the movies located on the iMac? If not, then you may want to try importing shorter length clips.

When importing, be sure the import has time to finish.

Be sure you are following the steps for importing found here: Import media into iMovie from your Mac - Apple Support

Have a good day.