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 where an advertisement is to be inserted into media content and a second indication comprising at least one of an end time of the advertisement or a duration of the advertisement. The advertisement insertion tool inspects a first original slice of the media content that contains the media content at the start time to locate a first key frame at or prior to the start time and creates a first new slice comprising the media content of the first original slice up to the start time. The advertisement insertion tool inspects a second original slice of the media content that contains the media content at the end time to locate a second key frame at or prior to the end time and creates a second new slice comprising the media content of the second original slice after the end time until an end of the second original slice.