Computer-implemented systems and methods are provided for defining ad space in a video. For example, a computer can receive an identification of a video and an advertisement space definition that includes a time stamp for the advertisement space in the video and an advertisement length. The computer can receive a request to view the video. The computer can determine an advertisement to play in the advertisement space such that the advertisement is not longer than the advertisement length included in the video's advertisement space definition. The computer can provide access to the video, and when the video reaches the time stamp, the advertisement is played in the advertisement space.