Video links in email, or even videos that play directly in email, have been a hot topic lately, so I figured I'd ask this here. I've tended to use the triangular play button over thumbnails when a video can play directly in the email, and a more descriptive button in cases where the video will open elsewhere. The other benefit of the more descriptive button is that you can use it without dropping it directly over the center of the image and still have it be intuitive.
At the end of the day, though, which type of button is most effective when used in emails?