How do I allow only a subset of students to view a video?

Follow the directions to "hide videos from students using a private folder". This will leave you with a folder that does not allow any/every student to view its contents. From there, if you wish for a particular student or students to have viewing capabilities, you can add them individually as "Viewers" by email in the section labelled "Add people and groups".

This may be useful in cases in which you wish to share recordings only with a subset of students (e.g. those who couldn't attend a live session).