Some embodiments provide a media-editing application that includes several background-rendering modules. These modules automatically render segments of a media presentation in the background of a system on which the media-editing application is being executed. By performing rendering in the background, the background-rendering modules produce rendered results for the segments. That is, the modules pre-generate playable media output data (e.g., composite video frames or audio samples) of the media presentation without interrupting other operations (e.g., editing operations, etc.) of the media-editing application. The background-rendering modules in some embodiments include a first background-rendering module and a second background-rendering module. The first background-rendering module determines a prioritized order in which the segments are to be rendered. The second background-rendering module renders the segments of each category in the prioritized order that is determined by the first background-rendering module.