There is a talking cat app well known for iOS devices, in which you speak your voice and he repeats. Analyzing this app, you'll see that it stops talking when you stop talking, that is, it stops to capture the audio when not receive another voice.
I was giving a analyzing the methods of AVAudioRecorder class, and not found any method in which to capture when the User stop to talking or recorder stops to receive external audio.
How can I capture when the audio recorder stops to receiving audio.
Process the audio stream as it is coming through. You can look at the frequency and volume of the stream. From there you can determine if the user has stopped talking.
I suggest frequency and volume as the recorder still picks up background audio. If the volume drops dramatically then the sounds the recorder is picking up must be further away from the device than before. The frequency can also lend itself to:
A.) Filter out the background audio in the audio used to replay the audio with a pitch change or any other changes. etc. B.) I do not know the limits of frequency for the average human. But this covers the use case where the user has stopped talking, but have moved the device in such a way that the recorder still picks up load shuffling from moving fingers near the mic.