The online lectures you are talking about are the ones on youtube. They are not the same as the ones used in ml-class.org. The latter ones are in a completely different format.
It is not just a recording of a "normal" lecture...
I am talking about the open courseware offered here http://openclassroom.stanford.edu/MainFolder/HomePage.php I am unsure if these are the same videos offered on youtube, however by taking a glance at the website it looks like they are the exact same classes.
If I understood correctly, those were a predecessor of the current lectures. I had no problems with audio missing.
(but yes quality could have been better)
It is not just a recording of a "normal" lecture...