Systems and methods are described for server-side manipulation of underlying video content in order to dynamically place overlay content within a video stream in a manner whereby a viewing user sees the advertisement content over or integrated within a portion of the base video content. Segments of the original video file may be modified by a server to display overlay content over a portion of the original content, and a revised manifest file may be generated by the server and sent to a client device. The revised manifest file may cause a video player on the client device to present in sequence (a) a first original portion of the video, (b) a second portion of the video modified to include overlaid advertisement content or other overlay content within the second portion, followed by (c) a third original portion of the video.