One of the worst parts of audio and video lectures is that most live events were never meant to be very effective presentations. At the HigherEdBlogCon this week Mart Ott (Jackson Comm College;http://www.docott.com gave a nice example of a better way to do this work. He describes a process of using PowerPoint slides or other visual aid along with a nonclassroom-recorded audio track.
He provides lots of reason why this is much better to listen to or watch.
I think the most important idea in this presentation is his point of breaking the lecture into smaller parts. He suggests that this mini-lectures are 5-15 minutes in length and cover one or two ideas. We have to remember that the classroom lecture was created to fit in a particular time and place-- a classroom, a place in which students move in large numbers from one physical location to another. Once that learning is taken out of the particular space and distributed in an asynchronous method, there is no reason to fill up any particular block of time. In fact, most audio and video learning needs to be broken up into small, more managable segments. It needs to have detailed descriptors so that learners can quickly figure out what to expect from a given piece. It probably also needs to be transcribed into print for those learners who would rather read something at their own pace rather than listen to someone else talk through the topic.