In the case of, for example, birthday and wedding recordings, what do you call the people who are the main focus of the video (e.g. bride, groom and birthday boy/girl)?
All the [……] of the videos shared something in common.
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If you're talking about everybody in the video you could say "the entire cast of the video".
For a single person you can use protagonist
the leading character or one of the major characters in a play, film, novel, etc.:
..or you can indeed have multiple protagonists.
If that is too cinematic for your needs, you could use subjects as suggested by @mplungjan or something like:
All of the people featured in the videos...
Or, if you want to highlight the key people you can use stars as answered by Mark. This would suggest the main "characters" and not those in the background.