Over the past several weeks we have been working on adding audio support to the client for both live and archived events. There is still some work to be done, but we want to start getting feedback from the community.
This new audio code is based on the latest stable client (2.1.7). Currently we have support for OS X and Windows and currently only (some) network cameras are supported. You need to enable audio support in the IP camera properties for each camera (see images below).