It so happens that iOS devices will not download the audio lectures because of how iOS conforms to software protocols. iOS does not allow certain files to be played in Safari, and wants those files to be opened in an app. For whatever reason, iOS does not recognize audio files should be played in an audio player, even though it does recognize that pdfs should be opened in iBooks or another app. So, for the time being, since the issue is with Apple's iOS, we are looking into an alternative solution.

For now, we recommend that iOS users download the audio lectures on another device.