Podcasting is a term used to describe a collection of technologies for automatically distributing audio and video programs over the internet using a publisher/subscriber model. It differs from earlier online collections of audio or video material because it automatically transfers materials to the user's computer for later consumption; it is one example of push technology. Podcasting enables independent producers to create self-published, syndicated "radio shows," and gives broadcast radio or television programs a new distribution method.
A podcast is generally analogous to a (non-live) television or radio series. The content provider begins by making a file (for example, an MP3 audio file) available on the internet. This is most frequently accomplished by posting the file on a publicly-available webserver; however, other means, such as BitTorrent trackers, are known to be used, and it is not absolutely necessary that the file be publicly accessible. Technically, the only requirement is that the file be accessible through some known URI (a general-purpose internet address). This file is often referred to as one episode of a podcast.
A consumer enters this feed URI into a software program called a podcatcher or aggregator (the former term is specific to podcasting while the latter is general to all programs which collect news from feeds). This program retrieves and processes data from the feed URI.
A podcatcher is usually an always-on program which starts when the computer is started and runs in the background. It manages a set of feed URIs added by the user and downloads each at a specified interval, such as every two hours. If the feed data has substantively changed from when it was previously checked (or if the feed was just added to the podcatcher's list), the program determines the location of the most recent episode and automatically downloads it to the user's computer. Some podcatchers, such as iTunes, also automatically make the newly downloaded episodes available to the user's portable media player, if applicable. (This is only the typical behavior of a podcatcher; some podcatchers behave—or can be set to behave—differently.)
The downloaded episodes can then be played, replayed, or archived as with any other computer file.