https://www.theverge.com/2018/11/16/18098474/facebook-messenger-watch-videos-together-feature-test

Facebook launched its Watch Party feature earlier this year, which lets people in a Facebook Group watch videos in sync, commenting and reacting together. According to some new code added to Messenger, spotted by developer Ananay Arora, the company may be expanding a similar sort of feature to Messenger chats, via TechCrunch.

  
  
    Image: Ananay Arora (via TechCrunch)
  

Based on the spotted code snippets, it seems like the “Watch Videos Together” feature would work a lot like Watch Party: drop a video in Messenger, and you’ll be able to ping the person (or group of people) in your Messenger thread so you can watch it at the same time. Presumably, Facebook is planning to support this feature for videos that are hosted on Facebook, which means that you probably won’t be able to use this for, say, hosting a remote movie night with your friends on Netflix.