Desktop Wallpaper

Image / HTML5
File size: max 100 kb
Mobile 320x320 file size: max 60 kb
Format: jpg, gif, png, html5 or 3rd party script
Newsletter: 500x200 pixels, max 80 kb
Newsletter format: gif, jpg
Html5 guidelines: https://support.google.com/admanager/answer/7046799?hl=en
Html5 validator: https://h5validator.appspot.com/dcm/asset
 
Video
Video format (.mp4, h264, no audio)
File size: max 1 mb
 
Wallpaper 
Template: PSD / JPG
File size: max 400 kb
Format: jpg, png