How podcasting works

Below is a diagram which illustrates the various components involved in delivering and receiving a podcast (click on the image to view a larger version in a new window).

Diagram of podcasting components - link to a larger version (opens in a new window)

Each component is described in more detail below:

Digital audio file - A podcast will involve a number of digital audio files hosted on the Internet. Each podcast episode is represented by one of these files. In general these are audio files encoded in a standard format such as MP3 so that they can be played on the majority of digital media players and PCs.

Podcast feed - This is a simple file which basically consists of a list of the podcast episodes with some additional descriptive information called metadata. This metadata provides details of the podcast and also details for each episode which helps a listener decide whether to subscribe to the podcast and then which episodes to listen to. For example:

  • Title of the podcast
  • Description of the podcast
  • Author of the podcast
  • Title of the podcast episode
  • Summary fo the podcast episode
  • Date of publishing of the podcast episode
  • etc...

This file also includes the details of where the media file for each episode is located on the Internet (given as a web address e.g. http://www.mypodcast.com/episode1.mp3) so the podcast aggregator software knows where to find it.

Feeds are generally automatically generated and written in code called XML conforming to a standard such as RSS (Really Simple Syndication). Part of a simple example podcast feed is shown below (don't worry if this appears complex, you won't have to write this to create a podcast!):

Example podcast feed

Podcast aggregator software - This is PC based software that provides specific functionality for subscribing to and receiving existing podcasts. Typical functionality of this software includes:

  • Subscribing to a podcast feed.
  • Regularly checking subscribed podcast feeds for updates.
  • Alerting the listener when a new podcast episode becomes available.
  • Downloading the episode file from the Internet.
  • Playing the audio file.
  • Transfering the audio file onto a portable media player (e.g. synchronising with an iPod).

There are many software packages that provide this functionality most of which are free e.g. iTunes & Juice.

Note - there are also web-based podcast aggregators (e.g. Podnova) which provide similar functionality via a secure website. These systems do not download and transfer the podcast episodes on to a portable playing device and therefore require podcast episodes to be listened to on a PC that is on the Internet.

Portable digital media player - a small electronic device that stores and plays audio files. The most well known example is the iPod but there are many others such as Sony Walkman, iRiver and Creative Zen. In addition many modern mobile phones can receive and play podcasts.

Podcast receiving scenario

The diagram and scenario below illustrate how a podcast works. This illustrates that once the podcast feed URL has been found on the Internet and subscribed to with aggregating software, the process of new podcast episodes being discovered and downloaded is cyclic and largely automatic. The podcast listener can then choose to listen to each episode on their PC or with a portable player.

Diagram illustrating steps in receiving a podcast

Female student wearing an iPodJenny has been recommended a podcast by a friend and has been emailed the web address of the podcast feed. She opens her podcast aggregator software and clicks subscribe to a new podcast. She pastes the feed web address into a text box and clicks OK.

The aggregator software then accesses the feed file over the Internet and finds that several podcast episodes are already available. It displays a list of these episodes and asks if Jenny would like to download a selection or all these episodes. She chooses to download all the episodes.

After the downloading is completed Jenny decides to listen to the first episode at her PC using her podcast aggregator software. She double clicks on the downloaded episode.

The podcast seems interesting and Jenny would like to listen to more episodes using her portable media player. She connects the player to her PC and uses her aggregator to transfer the podcast episode audio files. She then disconnects her player and can listen to the podcast episodes on her next bus journey to college.

The next day when Jenny turns on her PC, her podcast aggregator software checks the podcast feed again and discovers that a new podcast episode has been published. The software automatically displays a message to alert Jenny to the new episode and asks if she wants to download it. She clicks yes and after the file has downloaded she again connects her portable media player to the PC and transfers the new episode so she can listen to it on her next bus journey.

Next - RSS simplified