A radio station transmits its broadcast audio content, including audible advertisements, to listeners over the Internet via an Internet Hosting Service that provides listener access to radio station content. A computing system at the radio station digitizes the audio, and supplies marking information that identifies the beginning and duration of commercials. The digital marking information is supplied with the radio station's audio to the Internet Hosting Service. The Internet Hosting Service maintains a repository of replacement audio commercials along with information about the commercials including duration. Upon receiving the digital marker indicating the presence of a commercial, the Internet Hosting Service selects a replacement commercial of comparable duration from its repository.