1. A computer-implemented method, comprising: accessing data defining an animation sequence, the animation sequence depicting motion of at least one object over time; accessing data identifying animation primitives supported by a markup language; analyzing the data defining the animation sequence to determine a first portion of the animation sequence that can be represented using a set of visual assets animated using animation primitives and a second portion of the animation sequence that can be represented by using a scripting language to control transitions between frames representing the second portion, and generating a package, the package comprising markup code referencing the visual assets and defining an appearance of the frames, a stylesheet referencing the animation primitives, and a structured data object, the markup code generated to cause a rendering application to provide the animation sequence by using the scripting language to coordinate rendering of each of the first portion and the second portion according to a parameter included in the structured data object, the first portion rendered by applying the animation primitives as styles to the set of visual assets and the second portion rendered by drawing the plurality of frames and transitioning between the frames using the scripting language.