Web Design & Development Guide


Video podcasts

A podcast is a digital media file, or a series of such files, that is distributed over the Internet using syndication feeds for playback on portable media players and personal computers. A podcast is a specific type of webcast which, like 'radio', can mean either the content itself or 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. The term "podcast" is a portmanteau of the name of Apple's portable music player, the iPod, and broadcast[1]; a "pod" refers to the iPod, and "cast" to the idea of broadcasting.

In other words, a podcast is a collection of files (usually audio but may include video) residing at a unique web feed address. People can "subscribe" to this feed by submitting the feed address to an aggregator (like iTunes - software that runs on the consumer's computer). When new "episodes" become available in the podcast they will be automatically downloaded to that user's computer. Unlike radio or streaming content on the web, podcasts are not real-time. The material is pre-recorded and users can check out the material at their leisure, offline.

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, using an aggregator or feed reader capable of reading feed formats such as RSS or Atom.

Certain podcasts can even be live and interactive. Dozens of podcast enthusiasts can be on at once, with the "host" being able to control their audience in the same way a radio host can.


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. It works exactly like any newsreader 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. 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.

In March 2006 it was reported that 80% of podcast "episodes" are "consumed" on the PC onto which they are downloaded i.e. they are never actually transferred to an iPod or other portable player, or are deleted from the PC without being listened to.[2] However, the latest version of the iTunes program will stop downloading new podcasts that have been subscribed to if it detects they are not being listened to. Thus the percentage of unlistened podcasts is controlled through this mechanism.

To conserve bandwidth, users may opt to search for content using an online podcast directory. Some directories allow people to listen online and 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.

Managing Podcasts on an iPod

Only the latest un-listened podcasts are put in this playlist. The user can thus ensure that all news programs are new and current and also un-listened. This playlist is sychronised regularly with the iPod.
Only the latest un-listened podcasts are put in this playlist. The user can thus ensure that all news programs are new and current and also un-listened. This playlist is sychronised regularly with the iPod.

iTunes offers the ability to create "Smart Playlists" which can be used to control which podcasts are in the playlist using multiple criteria such as date, number of times listened, type, etc. It is also possible to set up iTunes so that only certain playlists will be synched with the iPod. By using a combination ot the two techniques it is possible to control exactly which music and/or podcasts will be transferred to the iPod. The illustration to the right shows one such "Smart playlist" which ensures that only the latest un-listened podcasts will be in the smart playlist. Any podcast which is more that two weeks old is not included, nor is any podcast that the iPod user has already listened to. This smart playlist is synched with the iPod every time the iPod is plugged into the pc ensuring that the user does not have to listen to the same show more than once. Once a podcast has been listened to, it will be removed from this list as soon as the iPod is synched with the PC. There are many criteria which can control what goes in a smart playlist, such as "name", "artist", "category", "grouping", "kind", "last played", "play count", "rating", "last skipped" and "playlist" and these can be combined with funtions such as "equals", "is greater than", "is less than", "contains", "is true", "is false", "is", "is not", "does not contain", "starts with", "ends with", "is in the range" "is before", "is after". As a result it is possible to control exactly which podcasts are transferred to the iPod.


For example, a user may only want news programs less than 24 hours old, unlistened science programs less than one month old, and all Spanish lessons that he/she has yet listened to less than three times. By using smart playlists, she/he can ensure that these rules will be followed. The user would set up four smart playlists. The first smart playlist containing news podcasts downloaded in the last 24 hours, the second containing the science podcasts which are unlistened and less than one month old, and a third smart playlist containing Spanish lessons which have been listened less than three times, and a fourth smart playlist which contains the contents of the first three. The fourth smart playlist is the one which would be synched with the iPod. Obviously the fourth playlist may contain many other play lists as well as the ones described above.

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,[3] official and unofficial audio tours of museums, conference meeting alerts and updates, and by police departments to distribute public safety messages. For example, the Pediaphon project provides dynamically generated podcasts of all English, French and German language Wikipedia articles.

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 talks, vocabulary or foreign language lessons, international pen pal letters (podcast pals!), music performance, interviews, debates. Podcasting can be a publishing tool for student oral presentations. Video podcasts can be used in all these ways as well.


In February 5, 2005, Shae Spencer Management LLC of Fairport, New York filed a trademark application to register PODCAST for an 'online prerecorded radio program over the internet'.[4] In 2005-9-9, United States Patent and Trademark Office rejected the application. The rejection notice cited Wikipedia's Podcast entry had described the history of the term.[5]

As of September 19, 2005, known trademarks that capitalize on podcast include: Podcast Realty, GuidePod, PodGizmo, Pod-Casting, MyPod, Podvertiser, ePodcast, PodCabin, Podcaster, PodShop, PodKitchen, Podgram, GodPod and Podcast.[6]

As of February 2007, there have been 24 attempts to register trademarks containing the word 'PODCAST' in United States, but only 'PODCAST READY' from Podcast Ready, Inc. was approved.[7]


In November of 2004, Pittsburgh-based podcast hosting service Liberated Syndication was launched. The company, also known as Libsyn, was one of the first podcast hosting companies on the scene.

In 2005, it was reported that Adam Curry had anonymously edited the podcasting entry on Wikipedia to remove credits from other people and to inflate his role in its creation.[8] The business model of Curry's podcasting network Podshow has since been criticised by many in the industry, and has been accused of exploitative practices in its dealings with independent podcasters.

In September 26, 2006, It was reported that Apple Computer started to crack down on businesses using the word 'pod' in product and company names. Apple sent a cease-and-desist order that week to Podcast Ready, which markets an application known as myPodder.[9] Lawyers for Apple contended that the term 'pod' has been used by the public to refer to Apple's music player so extensively that it falls under Apple's trademark protection.[10] It was speculated that activity was part of a bigger campaign for Apple to expand the scope of its existing iPod trademark, which included trademarking 'IPODCAST', 'IPOD Socks', 'POD'.[11] On November 16, 2006, Apple Trademark Department returned a letter claiming Apple does not object to third party usage of 'podcast' to refer to podcasting services, and Apple does not license the term.[12]

See also

Syndication protocols


External links

Lists of podcast directories: (not individual directories)

News aggregators
Video bloggers
Web syndication formats

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