When i want to make a Background in a specific row,at the moment for the video as background option, there is not the function to adapt the alternative image to the different browsersizes  like in the normal image option. So in browsers which don't display my BG video you see the alternative Bg picture,but it's stretched in wide browsers and cropped in small browsers like a mobile phone,which makes the BG video function almost useless.I hope your developers can fix that in a future update.