It's worth nothing that the reason security researchers haven't just intercepted the traffic from the Facebook apps to see if its transmitting voice data is because the apps use Certificate Pinning, which prevents the SSL traffic from being decrypted using the SSL certificate generated by mitmproxy/Charles.
In light of that restriction, what might be interesting is looking at the amount of data transferred by the Facebook app with/without the microphone/location services enabled. (this is a data project I have in the pipeline)
In light of that restriction, what might be interesting is looking at the amount of data transferred by the Facebook app with/without the microphone/location services enabled. (this is a data project I have in the pipeline)