User-applied, in-stream association of media content with a video content item is disclosed. During presentation of a video content item, a user selects or otherwise identifies a media content item to be associated with the video content item. The user further selects or otherwise identifies a temporal position (e.g., time value) within the video content item with which the media content item is to be associated. In one example, a user selects and drags the media content item to or toward the video content item within a GUI to define the association. In at least some implementations, the video content item may be presented via a different device than the media content item, thereby forming a multi-platform association.