Gmail video ads
I´ve seen (since a week or so) that it is possible to add a video to your Gmail ad template, instead of just an image (I am not referring to custom html Gmail ad, by which you could always add a video).
However, it´s not clear to me if this video will (auto?) play in the mail utself, or if it will just be an image looking like a video, which if you click it will send you to the video on YouTube. Because that is how it appears in the preview...
Re: Gmail video ads
You can find the answer at the bottom of this Help Center article about Custom HTML for Gmail ads--essentially, the video will play in a lightbox in Gmail when a user clicks on the video still.
Hope this helps,