A system modifies video by embedding portions of media, such as subsets of image pixels, in video frames. When the video is played at normal speed, the media is not discernible. However, when the video is played at an accelerated rate in the forward or reverse direction, the portions of images embedded in video frames coalesce into discernible media. The embedded media may be simple text, images, video, audio, or other media. The system may also evaluate base videos as well as insertion media using neuro-response measurements to determine how and what type of media to embed. The media may be embedded in real-time or near real-time into video for delivery to a user for playback on devices such as digital video recorders, computer systems, software and hardware players, cable boxes, etc.