Methods and systems for advertisement insertion into streaming media content are described. In one method, an advertisement insertion tool receives a first indication of a start time of an advertisement break to be inserted into a stream of slices of media content. The advertisement insertion tool identifies a first slice of the slices that encompasses the start time of the advertisement break. The first slice comprises video frames. The advertisement insertion tool truncates the first slice to contain the video frames up to the start time of the advertisement break. An advertisement can be inserted after the truncated first slice and before a next second slice in the stream.