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It wouldn't exactly be synced to ZM, but I'm sure you could setup VLC daemons on your machine to pull down and save the audio from the RTSP stream if you needed them for something later. You'd have to open them separately, but how often will you be watching recorded video in ZM and need to know what's being said?
It wouldn't be rocket science to setup a script to time-date-camera stamp the audio files and save them somewhere logical, even throw an entry into a mysql table mentioning it. If you want it, I'd try that route.
One should consider legal consequences of audio capture as well. Here it is illegal to record conversation without written consent from person/s being recorded unless it is police doing that with court permission
if common sense is so uncommon, why is it called common then?
Just a thought; Depending on the quality of the audio (not high on my Axis 207's, but I don't use it), it might also be useful for AudioDetect in areas where MotionDetect doesn't work well.