My movie maker seems to generate corrupt files. saveFrame() works fine, and there are no error messages during movie generation. VLC will open the video without error.

The generated generated file's icon is the quicktime logo – not a preview, as macOS usually displays. Upon opening, I get this error message:

The document “out.mov” could not be opened. The file isn't compatible with quicktime player.

I am running Processing 3.5.4 on MacOS Catalina 10.15.7