Podcasting



Podcasting is the method of distributing multimedia files, such as audio programs or music videos, over the Internet using either the RSS or Atom syndication formats, for playback on mobile devices and personal computers. The term podcast, like 'radio', can mean both the content and the method of delivery. The host or author of a podcast is often called a podcaster. Podcasters' web sites may also offer direct download or streaming of their files; a podcast however is distinguished by its ability to be downloaded automatically using software capable of reading RSS or Atom feeds.

Usually a podcast features one type of 'show', with new episodes released either sporadically or at planned intervals such as daily or weekly. In addition, there are podcast networks that feature multiple shows on the same feed.

History
The concept of podcasting was suggested as early as 2000 and the technical components were available by the start of 2001, but it wasn't until 2003 that regular podcasts started showing up on well-known Web sites. The concept quickly took off and by the end of 2004, thousands of podcasts were available and the term had entered the public domain.

Name
"Podcasting" is a portmanteau coined in 2004, that combined two words: "iPod" and "broadcasting." Even though the name is a misnomer, in that podcasting doesn't require an iPod and no over-the-air broadcasting is required, it has maintained its prominence in the face of numerous alternatives.

The use of "podcast" to describe both audio and video feeds seemed natural to some users, while others prefer to reserve the word for audio and coin new terms for video subscriptions. Other "pod-" derived neologisms include "podcasters" for individuals or organizations offering feeds and "podcatchers" for special RSS aggregators with the ability to transfer the files to media player software or hardware.

The "pod" name association came about because Apple Computer's iPod digital audio player was popular when podcasting began. The use of "pod" in 2004 probably played a part in Apple's development of podcasting products and services in 2005, further linking the device and the activity in the news media.

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". Various writers suggested other names or alternative interpretations of the letters "P-O-D." Technology writer Doc Searls had proposed "Personal Option Digital" in September, 2004. The "Personal on Demand" interpretation was in international circulation as early as October 2004. In July 2005, Microsoft blogger Robert Scoble mentioned that interpretation while countering reports that his company was pushing the word "blogcasting" to avoid mentioning an Apple product. "Blogcasting" also implied content based on, or similar in format to, blogs, which was not always the case. Other terms have been suggested, but had shortcomings — "audioblogging", "audio magazines" and "webcasting" could describe other forms of media distribution, and "rsscasting" would be difficult to pronounce. As use of RSS enclosures for video spread in 2005, podcasting of video data was called, among other things, "video blogging", "video podcasting", "vidcasting", "vlogging", "vodcasting", "vicasting", and "videocasting".

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 by which 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.

A podcast is generally analogous to a recorded television or radio series.

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 machine-readable list of the URIs 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 dates, 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 to a known location on a webserver. (Unlike the episode file itself, the feed is published to a webserver, usually not by other means.) 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 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 item and automatically downloads it to the user's computer. Some podcatchers, such as iTunes, also automatically make the newly downloaded episodes available to a user's portable media player. (This is only the typical behavior of a podcatcher; some podcatchers behave&mdash;or can be set to behave&mdash;differently.)

The downloaded episodes can then be played, replayed, or archived as with any other computer file.

Variants of the podcast include the marcast or Podcast Marketing. Podcast Marketing is the method of creating and publishing audio and video programs via the Internet. It allows a company's or marketer's users, clients, and customers to subscribe to a feed of new information about products and services.

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 and then downloading a huge amount of content, only to find out later that they didn't have any interest. For most broadband users, bandwidth is generally not a major consideration; however, there are still a number of computers that are connected to the Internet using a dial-up connection.

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.

Notes and references
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