Systems and methods of combining digital video are described. A system can receive digital video comprising frames. The system can analyze the frames to identify a subset of consecutive frames that have a static portion defined by a spatial region with matching pixels across two or more frames. The system can tag the digital video with an indication of the subset and a trigger that causes transmission, at a temporal offset during playback prior to the subset, of a request for content used to overwrite the static portion. The system can receive the request from the client device, the request transmitted by the client device based on the temporal offset during playback prior to the subset. The system can select and transmit a content item responsive to the request to cause the client device to render the content item at the static portion of the subset.