March 17, 2017
Google has begun rolling out a new improvement to Gmail desktop users that makes previewing video attachments in Gmail much smoother and quicker. Previously, in order to view a video attachment in Gmail, you would have to download it to your computer and open it with a media player. When opening an email with video attachments, you will now see a thumbnail of the video and have the ability to stream it, right from inside Gmail.
Note: this release may take up to 15 days for feature visibility.