Systems, methods, and apparatus include computer programs encoded on a computer-readable storage medium, including a system for ranking videos. Videos are identified that have been presented at client devices. For each video, session start data is identified that specifies a lead video that initiated presentation to a user during a presentation session. For each lead video, presentation times over multiple user sessions are determined, a scaled presentation time is obtained, user sessions for which the lead video initiated presentation of videos are identified, and an aggregate video presentation time attributable to the lead video is determined. For each given video, a presentation score is determined based on a scaled presentation time of the lead video relative to a sum of the aggregate video presentation times for the lead videos. The videos are ranked based on the presentation scores. A user interface is updated to present the ranked videos.