: MP4 is the most compatible format for mobile devices, laptops, and smart TVs.
While "Girls Forever" and the number 1366 appear in various contexts, they do not collectively refer to a single well-known media file or guide. 1366 is often a standard screen width (1366x768) or, in historical contexts, a year in the Islamic calendar (1366 AH corresponds to 1947 AD). "Girls Forever" is a common theme in pop culture, appearing in fan projects for shows like Harvey Girls Forever! or as a tribute to groups like the Spice Girls.
If your goal is to make an MP4 video fit a standard laptop screen resolution (1366x768):
: A sub-series of My Little Pony that frequently uses "Girls Forever" in its music videos and fan groups. 4. Safe Downloading & Storage