What is Podcasting?
Podcasting's initial appeal at Kid's Talk Radio was to allow individual students to distribute
their own "radio shows," but the system quickly became used in a wide
variety of other ways, including distribution of school lessons [5],
official and unofficial audio tours of museums, conference meeting
alerts and updates, and by police departments to distribute public
safety messages.
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.[6] 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.
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