A podcast is a collection of digital media files which is distributed over the Internet, often using syndication feeds, for playback on portable media players and personal computers. The term, like "radio", can refer either to the content itself or to the method by which it is syndicated; the latter is also termed podcasting. The host or author of a podcast is often called a podcaster. Though podcasters' web sites may also offer direct download or streaming of their content, a podcast is distinguished from other digital media formats by its ability to be syndicated, subscribed to, and downloaded automatically when new content is added, using an aggregator or feed reader capable of reading feed formats such as RSS or Atom. The content provider begins by making a file (for example, an MP3 audio file) available on the Internet through some known Uniform Resource Identifier. This is usually done by posting the file on a webserver; however, BitTorrent trackers also have been used. The files may be available to the general public or may only be available to certain users. The content provider then announces the existence of that file by referencing it in another file known as the feed. The feed is a list of the URLs by which episodes of the podcast may be accessed. This list is usually published in RSS format (although Atom can also be used), which provides other information, such as publish date, titles, and accompanying text descriptions of the series and each of its episodes. The feed may contain entries for all episodes in a series, but is typically limited to a short list of the most recent episodes, as is the case with many news feeds. Standard podcasts consist of a feed from one author. More recently, multiple authors have been able to contribute episodes to a single podcast feed using concepts such as social podcasting. A podcast-specific aggregator or podcatcher usually starts when the computer is booted and runs in the background. It works exactly like any aggregator which checks each feed at a specified interval, such as every two hours. If the feed data has changed from when it was previously checked (or if the feed was just added to the application's list), the program determines the location of the most recent item and automatically downloads it. The downloaded episodes can then be played, replayed, or archived as with any other computer file. Many applications also automatically transfer the newly downloaded episodes available to a user's portable media player, which is connected to the PC running the aggregator, perhaps via a USB cable. The publish/subscribe model of podcasting is a version of push technology, in that the information provider chooses which files to offer in a feed and the subscriber chooses among available feed channels. While the user is not "pulling" individual files from the Web, there is a strong "pull" aspect in that the receiver is free to subscribe to (or unsubscribe from) a vast array of channels. Earlier Internet "push" services (e.g., PointCast) allowed a much more limited selection of content. Making full use of podcasts' syndication features requires appropriate software, often referred to as a podcatching client. The dominant podcatching client is Apple's iTunes player. However, there are alternatives, including Microsoft's newly developed Zune Marketplace, Juice (multiplatform), Doppler (Windows), Podget (Linux) and Podracer (Linux). Some established audio players, such as AmaroK, Winamp and Mediamonkey also offer (sometimes limited) podcatching functionality. Podcasting's initial appeal was to allow individuals to distribute their own radio-style shows, but the system quickly became used in a wide variety of other ways, including distribution of school lessons,[4] official and unofficial audio tours of museums, conference meeting alerts and updates, and by police departments to distribute public safety messages. Podcasting is becoming increasingly popular in education. Podcasts enable students and teachers to share information with anyone at anytime. An absent student can download the podcast of the recorded lesson. It can be a tool for teachers or administrators to communicate curriculum, assignments and other information with parents and the community. Teachers can record book discussions, vocabulary or foreign language lessons, international pen pal letters, music performance, interviews, and debates. Podcasting can be a publishing tool for student oral presentations. Video podcasts can be used in all these ways as well.
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