mv4 or mp4 files put into a shared Photos folder all appear black and unnamed

Some video apps created a blank first frame for videos. You would need to go into Photos, select a video, click on the Edit button, select the left facing caret to the left of the play bar and move it until you get the first non-blank frame. That should let you add it to a Shared Album with the first useable frame showing.

enzymepudding wrote:

I am running macOS Monterey Version 12.1 on a 2019 MacBook Pro. Videos in Photos library and then in a public shared file. The file name is obvious in Photos but disappears in the shared folder.

That's normal. All metadata is stripped from photos that are added to Shared Albums. You're only workaround is to use the Markup feature of Photos' edit mode to add whatever text you would like to the photo itself.

Please read the following user tip and restate your question/problem in detail: 

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What Mac model and year do you have?

What system are you running?

Where are these video files? Are these videos in a Photos library or in folders on your hard drive?

All files must have a file name.