After deciding Apple's GarageBand was a little over engineered for adding slides to the audio of a lecture I looked around for an alternative.
One technology which has been around for years is SMIL. This web format was intended for multimedia, but has not proved popular. But it is supported by Apple's Quicktime and Real's player.
So I took the VGA resolution slides (640 x 480 pixels) in PNG format I had created for the podcast and created a small SMIL file with entries like this:
<audio src="http://....mp3" ... clipBegin="npt=00:02:13" ... clipEnd="npt=00:03:43" />
<a href="http://www..."> <img src="http://www.t..." region="slides" dur="92s" alt="Web on Mobile phones ..." /></a>
This says "play the MP3 audio file from 2 minutes 13 seconds into the recording and stop at 3 minutes 43 seconds. At the same time display Slide 4".
The clever bit about this is that you can combine existing images and audio from anywhere on the Internet, without having to re-encode them. Also you can virtually edit the audio, by selecting clips from it. My SMIL presentation is about ten minutes shorter than the MP3 audio recording, due to bits I skipped. Also the images are high quality because you can use lossless formats, rather than the lossy ones used for video formats.
The SMIL player goes and gets the audio and images from the web as needed. The catch is that if your Internet connection is not fast enough, there are gaps in the sound and blank screens if the audio or images do not arrive in time. I created another SMIL file from the second half of the first. This is the audio for my "Wireless Web System for an Avian Influenza Pandemic", talk. The catch is that the player has to skip though 24 minutes of audio to get to the relevant bit to play. Without some sort of streaming server, this will be slow and inefficient. Of course I could split the recording into two halves.
The other catch is that this format is not supported by the iPod, or any other hand held video player (as far as I know). But at least you can play the original MP3 audio on a hand held player. Does anyone really want to watch slides on a tiny screen?