systems address the problem of matching advertisers with an audience when broadcasting on the Internet. In the simplest terms, current ad insertion systems take the existing station audio, interrupt it, and replace it with new content for the Internet audience. The people who listen to a radio station on the air hear one set of ads, and listeners on the Internet hear another set of ads. systems are designed to work with your radio station as is for the most part, so you don't have to dedicate any studio resources to programming a separate Internet feed.
In operation, an ad insertion system gets cues from station automation software so that it knows when the start and end of an advertisement block takes place. The ad insertion system can then switch over at the start of an advertisement block and substitute ads for the Internet audience in the place of the local on-air ads. The system has the smarts to queue up ads that fit exactly within the time available for the ad block, and to do so in a way that the Internet listener doesn't suffer from rough transitions into and out of the inserted ads.
Managing smooth transitions between the live station audio stream, the stored ad files, and back to the live stream is one of the biggest technical hurdles that ad insertion systems have to deal with. In some vendors' systems, the ad substitution happens entirely in the audio domain. In this case, the ad insertion system is typically a piece of hardware located at the radio station that takes a feed of the station audio and receives control information from the station automation software. It is basically a smart audio switcher that stores the Internet-only ads locally and has some intelligence of its own in selecting which ads to play. Its output is an audio feed of the station's on-air signal with different ads for the Internet audience dropped in at the appropriate times. Because it is typically a self-contained piece of hardware, timing of transitions can be exact so that the Internet listener always hears smooth segues between the stored ads and the station audio.
Other systems work entirely in the software domain, like the example in the diagram. The client software used by the listener plays the stream of your station audio normally, and then switches to playing replacement ads from stored files when instructed to do so by the ad insertion system. When the replacement ad files are done playing, the client software reconnects back to the live radio stream. Because the client must switch between sources, and the stored ad files may come from anywhere on the Internet, the issue of lining up the replacement ads on top of the station's audio becomes trickier. Unpredictable network latencies in retrieving ad files, and in reconnecting to the live stream when the ad files are done playing, make it more difficult to maintain smooth transitions.
Most of the big name players don't currently provide a mechanism for switching between sources without some interruption in the audio. Software-based ad insertion systems use different mechanisms on both the server and player sides to address this shortcoming. Some ad insertion systems have the listener download additional software that does local ad caching, or uses mechanisms for pre-buffering ads at the server to minimize delays switching between the files and the live stream.
Ken Nosé is chief software architect of NeoSonic Industries, Cleveland.