Per: w3c/ttwg#116
Comment 3 (#545), 3
Simple animation can be embedded in an ARIB-TTML document with “arib-tt:keyframes” and “arib-tt:animation” elelments. The “arib-tt:keyframes” element specifies an object to be animated and its appearance such as a set of images, color, and size. The “arib-tt:animation” element specifies how the object specified by the “arib-tt:keyframes” element is animated such as duration, number of iteration, and transition effect.