Podcast
2007 Schools Wikipedia Selection. Related subjects: Websites and the Internet
A podcast is a multimedia file distributed over the Internet using syndication feeds, for playback on mobile devices and personal computers. Like 'radio', it can mean both the content and the method of delivery; the latter may also be 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 audio formats by its ability to be downloaded automatically using software capable of reading feed formats such as RSS or Atom.
History
The concept of podcasting was suggested as early as 2000 and its technical components were available by 2001, then implemented in the program Radio Userland . In 2003 regular podcasts started showing up on well-known Web sites and software support spread.
Name
The editors of the New Oxford American Dictionary declared "podcasting" the 2005 word of the year, defining the term as "a digital recording of a radio broadcast or similar program, made available on the Internet for downloading to a personal audio player".
The name has aroused some controversy for implying one needs an iPod to listen to podcasts, when in fact all portable media players will play them. Creative Technology, the makers of iPod competitor Zen, state on the ZENcast website that podcast is short for "Personal On Demand broadcast", a definition that didn't exist before its use by Creative.
Some alternate names have been proposed, most recently 'netcast', suggested by podcaster and technology journalist Leo Laporte, partly in response to cease-and-desist letters sent by Apple to companies and individuals using the word 'pod' in their product's names. None of the terms has yet received as wide a use as 'podcast.'
Mechanics
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.
Podcasting is an automatic mechanism whereby multimedia computer files are transferred from a server to a client, which pulls down XML files containing the Internet addresses of the media files. In general, these files contain audio or video, but also could be images, text, PDF, or any file type.
The content provider begins by making a file (for example, an MP3 audio file) available on the Internet. This is usually done by posting the file on a publicly available webserver; however, BitTorrent trackers also have been used, and it is not technically necessary that the file be publicly accessible. 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.
The content provider then acknowledges 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 show 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 the 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 public podcasting and social podcasting.
The content provider posts the feed on a webserver. The location at which the feed is posted is expected to be permanent. This location is known as the feed URI (or, perhaps more often, feed URL). The content provider makes this feed URI known to the intended audience.
A consumer uses a type of software known as an aggregator, sometimes called a podcatcher or podcast receiver, to subscribe to and manage their feeds.
A podcast specific aggregator is usually an always-on program which starts when the computer is started and runs in the background. They work exactly like any newsreader someone would use to manage other web subscriptions. 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 application's list), the program determines the location of the most recent item and automatically downloads it to the user's computer. Interestingly, it is estimated that perhaps only 20% of podcasts are actually consumed on portable media players; 80% are consumed on the PC onto which they are downloaded, or deleted from the PC without being listened to. Some applications, such as iTunes, also automatically make the newly downloaded episodes available to a user's portable media player.
The downloaded episodes can then be played, replayed, or archived as with any other computer file.
To conserve bandwidth, users may opt to search for content using an online podcast directory. Some directories allow people to listen online and initially become familiar with the content provided from an RSS feed before deciding to subscribe. For most broadband users, bandwidth is generally not a major consideration; it could fairly be stated that podcasting itself is a technology that came with the increases in global bandwidth and broadband popularity.
Other uses
Podcasting's initial appeal was to allow individuals to distribute their own "radio shows," but the system quickly became used in a wide variety of other ways, including distribution of school lessons, official and unofficial audio tours of museums, conference meeting alerts and updates, and by police departments to distribute public safety messages.