There are several reasons why it is generally not possible to download the recordings. For many lectures there are however podcasts made available on LMU on iTunes U which can be downloaded.
Apart from these cases all content is covered by the usual copyright laws. Systematic downloads of content of the UnterrichtsMitschau (slides, videos etc.), multiplication (copying) and allowing access through websites or other media (i.e. marketing on CD/DVD) are not allowed or must be authorized in writing by the UnterrichtsMitschau.