The newer links also have the affect of tying more activity to specific accounts and requiring viewers to log in, which allows access to be tracked and made a part of each user’s profile.
The way Private videos work now, that will kill any old links or embeds, plus it limits sharing to a maximum of 50 people — all of whom will need a Google account to view it.
For people who would prefer to keep sharing their old Unlisted videos with public links, embeds and comments, they can opt out on a per-account basis by filling out this form over the next month.