[Jack-Devel] How to capture audio from speaker?

Hi,  I'm writing an MacOSX app that is able to capture audio from speaker and save the audio file to disk in wav or whatever format for further replay. I googled a lot and found out that Jack might help me to do this kind of thing. Is there any tutorials for this? Should I download JackOSX? I have cloned jack2 source code and successfully build example-clients/capture_client.c . Could you give me some guide? Thank you very much