Two is a trend. Vine, the new social media app that allows you to post 6 sec video clips, has a square format. The videos are in a 1:1 aspect ratio. This follows Instagram, the popular photo sharing app that gives the user focus and colour filters to improve their images.
This trend arrives just at the time when wide-screen has become the standard, default aspect-ratio of choice for both video and TV. The footage generated by Apple iPhones, other cutting edge phone technologies, and the latest video cameras, all seem to be on the 2:1 ratio. Before the move to High Definition, TV and camcorder footage was all 4:3.
Why the change to 1:1 for Instagram and Vine? Perhaps because the ratio evokes Large Format photography. This conveys a seriousness, a permenance, and a respect for the art of photography… a useful quality to communicate in the ephermeral, digital world of online image sharing.