2008-08-19: A podcast is the audio or video equivalent of a blog with an RSS feed. Just as you can read a blog with an RSS client and automatically see new entries as they are posted, you can subscribe to a podcast with any "podcatcher" (podcast client) program and automatically hear new recordings as they are released. Blogs and podcast both use RSS, but a true podcast uses RSS in a specific way to be compatible with podcatcher software.

A podcast is set up so that iPods (thus the name podcast) and other players, with appropriate software, can automatically download the latest installments without the need for the user to look at text and click on links to start up a player and so on.

A podcast listener can hook up their iPod to their PC in the morning, sync it, head out the door for their morning drive or jog and listen to your new podcast (and others to which they have subscribed) with no further effort on their part. Subscribe once, listen forever (or until you unsubscribe).

Apple invented podcasting as a useful way to fetch new recordings to listen to on the iPod portable music player. With podcasting, an iPod can be conveniently updated with new musical performances or talk shows released by anyone on the Internet.

Podcasting has since grown well beyond the iPod. Many people keep up with a podcast via their favorite blog-reading site, such as LiveJournal's "friends page," without realizing that podcasts were originally meant for portable devices.

The key difference between a blog's RSS feed and a podcast's feed is the inclusion of the enclosure element, which specifies the audio or video file to be played. Without that, the podcatcher doesn't know what to play. You can attach text to a podcast, but bear in mind that users who are using portable audio players might never read the text.

Here's a bare-bones example of a valid podcast RSS feed. Notice that the size of the MP3 audio file must be included in the enclosure element. Also, Apple defined several new elements to carry subtitle, author, and summary information that some podcatchers can recognize and display.

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0">
<channel>
<title>Cat Sounds</title>
<link>http://www.example.com/catsfromspace</link>
<item>
<title>Tabbies from Tibet</title>
<enclosure
url="http://www.example.com/podcasts/catsounds_tibet.mp3"
length="989898" type="audio/mpeg"/>
<pubDate>Mon, 24 Jul 2006 16:21:00 GMT</pubDate>
</item>
... Additional item elements for additional episodes ...
</channel>
</rss>

This is a very simple example. There are many additional elements that can be used in a podcast RSS feed.

In addition to MP3 audio, podcasts can contain H.264 and MPEG-4 video in certain formats. For complete information, see Apple's podcast technical specification.

See also how do I make a podcast?

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