Assets metadata: Matrix required? I'd like to add very basic metadata to assets (Alttext, Caption..)

I noticed in volumes you can add custom field types – but they're not appearing when editing the entry. I found it can be edited in the assets view, but that's too complicated for editors.

If those values should be editable in the entry – should the matrix field type be used?
You could go for a lightweight content-builder. That would mean that you could and would create a matrix blocktype for each of your content elements i.e. one blocktype for image with all the metadata you could chew on as fields, another for say body with some props too and so forth.

That would also give your users some neat control over the document flow.

Then you would saw it seamlessly together on the template layer. Your Content-Editors will not feel a thing.