https://thenextweb.com/facebook/2018/06/06/facebook-copies-musical-lys-lip-syncing-functionality-for-live-video/

After stealing several features from Snapchat for use in its own app and in Instagram, Facebook is now taking a leaf out of Musical.ly’s book to introduce a lip-syncing feature in users’ live video broadcasts.

When you choose to shoot a live video on your phone in Facebook’s mobile apps, you’ll now find an option to include a popular song to lip sync with.