It's not streamed. It gets recorded, compressed, (voice effects if you want), encrypted on device, then piped through, reverse process, auto played on reciever end.

Also, once it's decrypted and played back, the message gets destroyed.

Small suggestion, maybe you should send a “key down” notice when you begin recording, that generates a subtle sound on the receiving end. This would act as something like a typing indicator on a text messaging client.