Check out http://en.wikipedia.org/wiki/Podcasting
Podcasting is the method of distributing multimedia files, such as audio programs or music videos, over the Internet for playback on mobile devices and personal computers. The distribution format of a podcast uses either the RSS or Atom syndication formats.
The term podcast, like "radio", can mean both the content and the method of delivery. The host or author of a podcast is often referred to as a "podcaster".
Podcasters' web sites may also offer direct download or streaming of their files, however a podcast is distinguished by its ability to be downloaded automatically using software capable of reading RSS or Atom feeds.
Usually the podcast features one type of "show", with new episodes either sporadically or at planned intervals, such as daily or weekly. In addition to this, 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 or watch when they want, where they want, and how they want.
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—or can be set to behave—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 given a second thought, however, there are still a number of computers which are connected to the Internet using a dial-up connection.
How Do I Podcast?
