Facebook serves 4bn videos a day. Although they - reportedly - count a video view after 3 seconds of autoplay, this is an amzing number (and also in this article, they say therer would be a 78% completion rate of Facebook video, but from my experience with Facebook insights for posted video, I doubt this). The major shift in newsfeed video is also visible in the amount of video that is uploaded instead of linked or embedded via YouTube.
The second link below says that in a survey among marketing executives in the US, Facebook seems to be more popular for video advertisers than YouTube now.
Funny story: Since autoplay works silently on Facebook, Hotels.com produced silent ads with subtitles.