Systems and methods for automatically inserting advertisements into source video content playback streams are described. In one aspect, the systems and methods communicate a source video content playback stream to a video player to present source video to a user. During playback of the source video, and in response to receipt of a request from the user to navigate portions of the source video (e.g., a user command to fast forward the source video, rewind the source video, or other action), the systems and methods dynamically define a video advertisement clip insertion point (e.g., and insertion point based on a current playback position). The systems and methods then insert a contextually relevant and/or targeted video advertisement clip into the playback stream for presentation to the user.