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About Podcasts


From Wikipedia, the free encyclopedia

Podcasting is the distribution of audio or video files, such as radio programs or music videos, over the internet using either RSS or Atom syndication for listening on mobile devices and personal computers. A podcast is a web feed of audio or video files placed on the Internet for anyone to download or subscribe to, and also the content of that feed. Podcasters' websites also may offer direct download of their files, but the subscription feed of automatically delivered new content is what distinguishes a podcast from a simple download or real-time streaming (see below). Usually, the podcast features one type of "show" with new episodes either sporadically or at planned intervalled such as daily, weekly, etcetera. Besides that there are podcast networks that feature multiple shows on the same feed.

Podcasting's essence is about creating content (audio or video) for an audience that wants to listen when they want, where they want, and how they want.

Podcasting versus broadcasting and streaming

Subscribing to podcasts allows a user to collect programs from a variety of sources for listening or viewing off-line, whenever and wherever is convenient. In contrast, traditional broadcasting provides only one source at a time, and the time is broadcaster-specified. While podcasts are gaining ground on personal sites and blogs, they are not yet widespread. One easy way to find podcasts is to use the Podcast Directory in iTunes; these automatically-updated podcasts can then be easily synchronised to an iPod for off-line listening.

"Streaming" files from the Internet can remove the specified-time restriction, but still offers only one source at a time, and requires the user to be connected to the Internet while playing the files. The ability to "aggregate" programs from multiple sources is a major part of the attraction of podcast-listening.

Unlike podcasts, streaming also can be used to broadcast live events over the Internet at the moment they occur.

Although streamed programs, like broadcast radio signals, can be recorded or captured by the receiver, their transient nature distinguishes them from podcast episodes, which arrive already in archived form. (This difference may make a podcast legally distinct from a webcast or streamed media file.)


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 epsiodes 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—or can be set to behave—differently.)

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, such as; Directories such as this 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 given a second thought, however, there are still a number of computers which are connected to the Internet using a dial-up connection.


Initial development

What makes podcasting unique from other digital audio and video delivery is the use of syndication feed enclosures. The concept was proposed in a draft by Tristan Louis in October, 2000[7], and implemented in somewhat different form by Dave Winer, a software developer and an author of the RSS format. Winer had discussed the concept, also in October 2000, with Adam Curry[8], a user of his software, as well as having other customer requests for audioblogging features. He included the new functionality in RSS 0.92[9], by defining a new element[10] called "enclosure"[11], which would simply pass the address of a media file to the RSS aggregator. Winer demonstrated how the feature would work by enclosing a Grateful Dead song in his Scripting News weblog on January 11th, 2001[12].

For its first two years, the enclosure element had relatively few users. Winer's company incorporated the new feature in its weblogging product, Radio Userland, the program favored by Curry, audioblogger Harold Gilchrist and others. Since Radio Userland had a built-in aggregator, it provided both the "send" and "receive" components of what was then called audioblogging[13][14]. All that was needed for "podcasting" was a way to automatically move audio files from Radio Userland's download folder to an audio player (either software or hardware [1]) -- along with enough compelling audio to make such automation worth the trouble.

While few developers of RSS-capable blogging software or aggregators made use of the enclosure element, in June 2003, Stephen Downes demonstrated aggregation and syndication of audio files in his Ed Radio application[15]. Ed Radio scanned RSS feeds for MP3 files, collected them into a single feed, and made the result available as SMIL or Webjay audio feeds.

In September 2003, Winer created a special RSS-with-enclosures feed for his Harvard Berkman Center colleague Christopher Lydon's weblog, which previously had a text-only RSS feed. Lydon, a former New York Times reporter and NPR talkshow host, had posted 25 in-depth interviews with bloggers, futurists and political figures, which Winer gradually released to the feed[16]. Announcing the feed in his weblog, Winer challenged other aggregator developers to support this new form of content and provide enclosure support. Not long after, Pete Prodoehl released a skin for the Amphetadesk aggregator that displayed enclosure links[17].

A month later, in October of 2003, Winer and friends organized the first Bloggercon weblogger conference at Berkman Center. CDs of Lydon's interviews were distributed as an example of the high-quality MP3 content enclosures could deliver[18]; Bob Doyle demonstrated the portable studio he helped Lydon develop[19]; Harold Gilchrist presented a history of audioblogging, including Curry's early role, and Kevin Marks demonstrated a script to download RSS enclosures and pass them to iTunes for transfer to an iPod[20]. Curry and Marks discussed collaborating. After the conference, Curry offered his blog readers an RSStoiPod[21] script that moved mp3 files from Userland Radio to iTunes, and encouraged other developers to build on the idea. The iPodder idea was picked up by multiple developer groups. While many of the early efforts remained command-line based, the first podcasting client with a user interface was iPodderX, developed by August Trometer and Ray Slakinski and released in mid-September, 2004. Shortly thereafter, another group (iSpider) rebranded their software as iPodder and released it under that name as Free Software.

The term "podcasting" was one of several terms for portable listening to audioblogs suggested by Ben Hammersley in The Guardian on February 12, 2004, referring to Lydon's interview programs ("...all the ingredients are there for a new boom in amateur radio. But what to call it? Audioblogging? Podcasting? GuerillaMedia?")[22]. In September of 2004, Dannie Gregoire also used the term to describe the automatic download[23] and synchronization of audio content; he also registered several 'podcast' related domains (e.g. The use of 'podcast' by Gregoire was picked up by podcasting evangelists such as Dave Slusher[24], Winer[25] and Curry, and entered common usage.

In September 2004, Curry launched an ipodder-dev mailing list, then Slashdot had a 100+ message discussion[26], bringing even more attention to the ipodder developer projects in progress at SourceForge. By October 2004, detailed how-to podcast articles[27] had begun to appear online, and a month later, liberated syndication libsyn launched what was apparently the first Podcast Service Provider, offering storage, bandwidth, and RSS creation tools.

In February, 2005 Carl Franklin, who had for the previous 2 years been publishing an audio talk show called .NET Rocks! started Pwop Productions, the first official podcast production company, which now produces podcasts for Microsoft and other companies.

Also in Feburary 2005, Australians Cameron Reilly and Mick Stanic started a Commercial Podcast Network, The Podcast network. Reilly described his vision for the network to be the Time Warner of New media. In November of 2005, they signed a Network wide sponsorship deal with Motorola.


The word about podcasting rapidly spread through the already-popular weblogs of Curry, Winer and other early podcasters and podcast-listeners. Fellow blogger and technology columnist Doc Searls began keeping track of how many "hits" Google found for the word "podcasts" on September 28, 2004. On that day, the result was 24 hits[29]. There were 526 hits on September 30, then 2,750 three days later. The number doubled every few days, passing 100,000 by October 18. A year later, Google found more than 100,000,000 hits on the word "podcasts."

On October 11, 2004 the first phonetic search engine for podcasting was launched called Podkey to assist podcasters to easily connect to each other. Capturing the early distribution and variety of podcasts was more difficult than counting Google hits, but before the end of October, The New York Times had reported podcasts across the United States and in Canada, Australia and Sweden, mentioning podcast topics from technology to veganism to movie reviews[30]. USA Today told its readers about the "free amateur chatfests" the following February [31][32], profiling several podcasters, giving instructions for sending and receiving podcasts, and including a "Top Ten" list from one of the many podcast directories that had sprung up. The newspaper quoted one directory as listing 3,300 podcast programs in February, 2005.

Those Top Ten programs gave further indication of podcast topics: four were about technology (including Curry's Daily Source Code, which also included music and personal chat), three were about music, one about movies, one about politics, and—at the time number 1 on the list—The Dawn and Drew Show, described as "married-couple banter," a program format that USA Today noted was popular on American broadcast radio in the 1940s. After Dawn and Drew, such "couplecasts" became quite popular among independent podcasts (those not derived from a preexisting radio show).

In November 2004, podcasting networks started to appear on the scene with podcasters affiliating with one another. The first was the GodCast Network, followed by the Tech Podcasts Network, the Association of Music Podcasters and others.

In March of 2005, John Edwards became the first national-level US politician to hold his own podcast[33]. Within a few episodes, the show had all the features of a major podcast: a web site with subscription feeds and show notes, guest appearances, questions from the audience, reviews and discussion of books, musical interludes of podsafe (noninfringing) songs, light banter (sports and recreation talk), even limited soundseeing from on location. Later in the summer of 2005, U.S. President George W. Bush became a podcaster of sorts, when the White House website added an RSS 2.0 feed to the previously downloadable files of the president's weekly radio addresses[34].

In May 2005 the first book on podcasting was released, the award-winning Podcasting The Do it Yourself Guide, by Todd Cochrane

By mid-2005, the medium had acquired backlash. Some experienced Internet users declared podcasting to be either nothing special (just a variant of blogs and mp3s), or already past its peak (because of growing exposure, and/or adoption by unsavvy Internet users).

In June, 2005, Apple staked its claim on the medium by adding podcasting to its free iTunes 4.9 music software and building a directory of podcasts at its iTunes Music Store. The new iTunes could subscribe to, download and organize podcasts, which made a separate aggregator application unnecessary for many users. Apple also promoted creation of podcasts using its GarageBand and Quicktime Pro software and the MPEG 4, m4a audio format instead of mp3.

In July 2005 the first People's Choice Podcast Awards were held during Podcast Expo. Awards were given in 20 categories.

As is often the case with new technologies, pornography has become a part of the scene, producing what is sometimes called podnography. Other approaches include enlisting a class full of MBA students to research podcasting and compare possible business models[35], and venture capital flowing to influential content providers.

The growing popularity of podcasting introduced a demand for music available for use on the shows without significant cost or licensing difficulty. Out of this demand, a growing number of tracks, by independent as well as signed acts, are now being designated "podsafe". (See also Podcasting and Music Royalties.)

In September 2005, the first podcast encoded in 5.1-channel encoded Dolby Headphone was created by Revision3 Studios with their 14th episode of Diggnation. The Dolby encoding lasted for only a few minutes of the podcast. On October 12, 2005 Apple Computer CEO Steve Jobs unveiled the first iPod with video capabilty. In his keynote speech he demonstrated the video podcasts Tiki Bar TV and Rocketboom. On December 3, 2005 Sony Computer Entertainment America announced that the PlayStation Portable would support podcasting using the RSS Channel feature after upgrading to 2.60.

In November 2005 the Podcaster News Network was launched that focuses on news and world events to include Sports, Business, Lifestyle, Politics, Religion and World and US National News.

"Podcast" was named the word of the year in 2005 by the New Oxford American Dictionary and would be in the dictionary in 2006.

The term "podmercial" was coined in early 2005 by John Iaisuilo, a radio broadcaster/podcaster in Las Vegas, who promptly trademarked it. The term "poditorial" was coined by author John Hedtke in July 2005 while writing half of "Podcasting Now: Audio Your Way!"

In February 2006 the first official Guinness Book of Records World Record for most popular podcast was awarded to The Ricky Gervais Show. The show, produced by the Guardian Unlimited and hosted by Positive Internet maintained an average of over a quarter of a million downloads per weekly episode.