.MOV files not opening on Mac

Is it an iMovie reference movie by chance? At least this user had a problem with "dvau" and it turned out to be an iMovie project that could be exported via MPEG Streamclip (32-bit app that works in Mojave or earlier, also via VMware in later macOS).

https://discussions.apple.com/thread/251714299

https://discussions.apple.com/thread/250492807

Modern QuickTime has moved away from older codecs. You will not be able to play legacy files in modern QuickTime Player.

• use a different video player (e.g. VLC).
• or convert the files to a QuickTime compatible format (H.264 video + AAC audio).

If HandBrake doesn’t see a valid source, then your file may be very weird or not a valid video file. HandBrake uses ffmpeg under the hood, which supports a lot of legacy codecs for input.

Please verify what Invisor Lite (or similar) can find out about the video files, as far as format and codecs.

Also check the file size for an expected value (e.g. a 16 KB file would be way too small to contain any video).

Old iMovie 1-6 created a reference.mov for its projects (and iDVD exports). That tiny .mov referenced the actual media .dv files with the edits the user made. AFAIR old iMovie versions stored all that in a plain folder while later versions used a package format to prevent careless users from fiddling with the contents.

If the project folder/package is still intact with media files, MPEG Streamclip should be able to drill inside even the project package (AFAIR with "Open Any" or a similar option in the file open dialog) and open the tiny reference.mov, play it in the edited form and export it in the desired format (deinterlaced H.264 suggested). An old 32-bit macOS Mojave or preferably earlier like High Sierra, El Capitan etc is the preferred platform but VMWare should do that as well.