Two words: popcorn.js rocks.
We’ve been working on adding record and playback to BigBlueButton 0.8 for months (we’re almost ready for a beta). We had originally written our own HTML5 playback client for playback of slides + audio. This way, playback could occur within an HTML5 browser. By using HTML5, the playback would be very lightweight: just a series of PNG images and an OGG audio file.
With the support of Mozilla, we converted over BigBlueButton to use popcorn.js (read: ditched our home grown client). The conversion went so well that we were able to add playback of chat messages.
Click the image below to see an example of playback of a recorded BigBlueButton session using popcorn.js.