Web Design & Development Guide
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; a "pod" refers to the iPod, and "cast" to the idea of
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
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
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
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
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
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.
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
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
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
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.
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. For
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.
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'. 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.
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.
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.
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
had anonymously edited the podcasting entry on Wikipedia to remove credits from
other people and to inflate his role in its creation.
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.
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
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'. 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.
Lists of podcast directories: (not individual directories)
Web syndication formats