With Lectopia a possible Nirvana for podcasting lectures, it was time to return to the here and now. Apple Australia had loaned me equipment to make a podcast, so it was time to make a podcast.
An audio Podcast is simple enough. What I wanted was an "enhanced" Podcast of a lecture. This would have the audio recorded in the lecture, plus slides and hypertext links to the notes. The Apple iPod plays such enhanced files in the form of MPEG4 files. Note that this is not MPEG video, but a separate part of the MPEG4 standard specifically for audio with pictures (called XMT).
The idea was to do the minimum of work needed to enhance the audio and to create the smallest, simplest most versatile content possible. No live video, as it takes a lot of setting up to produce, it takes a lot of bandwidth to play and doesn't add much to the experience. In any case I didn't have any video available from my lectures.
Slides are easy to create as still images from the screen presentation. When stored at VGA resolution (640 x 480 pixels) in PNG format, they only require about 20 kbytes each. This is about the resolution of a TV set and exactly twice the iPod screen size (QVGA 320 x 240) so should be acceptable for most purposes.
Most of the educational online content I have seen suffers from the problem of storing the images as JPEG or MPEG format. These are lossy formats designed for photographs. They make text and diagrams look blurry. Also they tend to be stored with a very large color range, which makes for bigger files. Most diagrams have a few dozen or few hundred colors.
One problem I had was that my "slides" are not Powerpoint, but a web page rendered with a special CSS style sheet. Without a built in capture system, I had to display each slide in the browser, then copy and paste the screen image to a paint program, crop, resize, reduce color range and then store as PNG.
Another problem is that I had neglected to include a marker in the presentation web page to mark the start of each slide, so I had to go back and add these. I then copied the web address of the slide and some text for the podcast. This would not be a problem for a Powerpoint or similar presentation, where there is a built in marker for each slide.
The most tedious part of the process is having to listen to the sound of my own voice, so I could mark the points where the slides, text and hyperlinks are inserted. It is tempting to then try and edit out all the audio blemishes out of the recording, but that would be a very time consuming process.
I did this with Garage Band, which came with the Apple Mac notebook computer. Garage Band was originally designed for recording and editing music. It has had a podcast track added, where you can insert "chapters", with images, text and hypertext links. Apple provide excellent online advice on how to create a podcast.
There were a few problems with this process. GarageBand is designed to give fine control over the audio. You don't really need this for podcast lectures. I found myself accidently selecting the wrong audio track, when I really only wanted one audio track. I would have liked to switch off most of the audio control features. In contrast I needed more control over inserting the chapters. Apple only provides a tiny space for this in the interface.
I tried it out on a couple of minutes audio and two slides and managed to play the result on the iPod. The sound was very good, but the visual display was unusable. The system had cropped the edges of my slides so the first few characters were missing. Also the text captions were placed over the bottom of the image, obscuring some content. It also appears that GarageBand had reduced my clear 640 x 480 PNG images to blurry little 160 x 160 JPEG.
Obviously I should have followed the advice I give others and included a "safe" blank border around each slide. But given the small size of the iPod screen, every pixel is precious. Perhaps there is a manual which explains why Apple does this, or even how to turn it off, but it seems an odd default behavior for the system.
GarageBand isn't really suitable for preparing podcasts of educational material. It might be good for preparing high art, or entertainment, but if you want to churn out dull, standardized material it is too flexible. This is much the same problem as with the average web creation software which makes it easy to insert lots of fonts, when what you need is a system which restricts you to a few standardized ones. You need a specific tool, such as the many add-ons for Powerpoint.
In my case I was trying to do things from first principles. So I needed to step back and try XMT's older brother: SMIL.