A media server machine may be configured to provide media content within a datastream. This datastream may be provided to a media device that is configured to present the media content on a display. Also, this datastream may contemporaneously contain an “app-sync indicator” for the media content. The app-sync indicator is a data structure that signals the media device to launch an application on a companion device. By providing the app-sync indicator contemporaneously with the media content in the datastream, the launching of the application on the companion device may be synchronized with the media content. The app-sync indicator may specify the application to be launched. Also, the app-sync indicator may specify supplemental content to be presented by the launched application on the companion device.