On the other hand, the end user can only distinguish two kinds of recommendations: (1) what is most popular over a period, and (2) what is similar to your most

On the other hand, the end user can only distinguish two kinds of recommendations: (1) what is most popular over a period, and (2) what is similar to your most recent few likes/buys. Besides, in a social media app, you can do whatever you want. To overcome limitations in (1), you can show whatever view counts you want. To overcome (2), you can take a video recorded a week ago, whose similarity you learned in a batch 3 days ago, and show it to a new user with a tag that says "1h ago."