.m4b files play audio but no video in QuickTime

I recently upgraded to Lion, after which QuickTime no longer displays the video with my .m4b files. It plays the audio fine, but none of the video slides that are in the files. I spent time on the phone with tech support, and all they could suggest was using another media player such as VLC. But that doesn't answer the questions as to why QuickTime no longer plays the video in .m4b files. Does anyone else experience this?