Originally Posted By: DWallach
"Duo is the video companion to Allo", end-to-end encrypted, and works on iOS and Android. The claimed novelty is that you get a video preview of your caller prior to accepting the call.

Listening to a podcast discussing this, it seems at the keynote they didn't indicate if the video preview will be limited to people in your contacts or not. If it's not, well Google might be going for first place in the TTP competition. (NSFW warning on that link for words mentioning human anatomy.)