You can do this with the WP Video Lightbox. It works perfectly with Revolution Slider.
What you would do is, rather than inserting the cover image as an image layer, you would use a text layer, and insert the short code that you build with WP Video Lightbox. The shortcode allows you to select an image URL as its anchor. When you input the short code into the text layer in Revolution Slider, it will look like a short code in the backend. However, when you actually publish the slide, the image shows up on the live site, and opens up the video perfectly within the lightbox (you specify the YouTube or Vimeo video ID within the shortcode as well).
Hope this helps.