iMovie: any .mov, .mp4 files are grey and can't be imported anymore?

Hmmmm. How did you do the conversion? To cover the bases: The way to convert AVCHD is to Control-click on the AVCHD package to open it. Inside the package you will see an AVDHD folder with a subfolder titled BDMV with a further subfolder in BDMV titled STREAM. The .mts files that contain the video are in the STREAM subfolder. Copy out the .mts files, and convert those to H.264, Mp4/AAC. Or, you may not need to covert the .mts files at all. First try copy-dragging them (drag while holding down the Option key) into an iMovie project timeline.

Also, be aware that not all Mp4 files work in iMovie. They must be Mp4/AAC. Handbrake will do that conversion by default.

-- Rich

For clarity, where are these files located when you try to select or double click on them? Are they gray before you click on them? What device was used to create the files? What is the audio format of the files? What steps are you taking to import them?

The files contain a codec that is not compatible with iMovie and QuickTimePlayer. I suspect it is because the audio is Mp3, with which for some reason iMovie users seem lately to be having iMovie compatibility issues. iMovie likes AAC. The .mov file format is a container that can have a varying assortment of codecs, so that all .mov files are not necessarily alike. Also, not all Mp4 video is compatible with iMovie. It must be Mp4/AAC.

One solution you can try is to convert one or two of the files 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.

I believe that VLC can do the conversion as well, although I have not used it for that purpose.

To preserve the original files, you might want to work with duplicate copies.

-- Rich

Great! Glad it worked for you. 😊

-- Rich