Realtime Microphone Input to Output on iOS with Swift

Introduction

In this article, we will explore how to capture and play back audio from a microphone in real-time using Swift for iOS development. We will delve into the world of AVFoundation, which provides a framework for working with audio and video on iOS devices.

AVFoundation is a powerful tool that allows developers to easily integrate various media-related features into their applications. In this article, we will focus specifically on how to capture audio from the device’s microphone and play it back in real-time.

Understanding Audio Streams

Before we dive into the code, let’s take a closer look at audio streams. An audio stream is a sequence of audio samples that are played back through a speaker or headphones. In this case, we want to create an audio stream from the device’s microphone and play it back in real-time.

There are several types of audio streams, including:

• AudioBuffer: This is a buffer that holds a sequence of audio samples. AudioBuffers can be used to process and manipulate audio data.
• AudioStream: This is a stream of audio samples that are played back through a speaker or headphones. AudioStreams can be created from an AudioBuffer using the AVAudioPlayer class.
• **AVAudioSession`: This is an object that manages the audio session for an app. It’s used to configure the device’s microphone and speaker.

Setting Up the Audio Session

To capture audio from the device’s microphone, we need to create an AVAudioSession object and configure it to use the microphone as the input source.

Here’s how you can do this:

let audioSession = AVAudioSession.sharedInstance()
audioSession.requestLegacyPowerForNewMusicPlaybackEnabled(true)

We also need to configure the audio session to use the device’s microphone. We can do this using the setCategory method of the AVAudioSession object.

Here’s how you can do this:

let category: AVAudioSession.Category = .record
audioSession.setCategory(category, options: .notifyOthersOnDeactivation)

Capturing Audio from the Microphone

To capture audio from the microphone, we need to create an AVAudioInputNode object and configure it to use the device’s microphone.

Here’s how you can do this:

let microphone = AVAudioInputNode()
microphone.installTapOnBus(_:_self, bus: 0)

We also need to set up a callback function that will be called whenever new audio data is available. This callback function will process the new audio data and add it to the output audio stream.

Here’s how you can do this:

func microphoneTapOutput(_ buffer: AVAudioPCMBuffer, sampleTime: TimeInterval) {
    // Process the new audio data here
    
    // Add the processed audio data to the output audio stream
}

Playing Back Audio

To play back audio, we need to create an AVAudioPlayer object and configure it with our output audio stream.

Here’s how you can do this:

let player = AVAudioPlayer(contentsOf: outputAudioStream)
player.prepareToPlay()
player.play()

Putting It All Together

Now that we’ve gone over all the different components involved in capturing and playing back audio from a microphone, let’s put it all together.

Here’s an example of how you can create an AVAudioSession object, configure it to use the device’s microphone, capture audio from the microphone, process the new audio data, add it to the output audio stream, and play back the audio:

import AVFoundation

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Create an AVAudioSession object
        let audioSession = AVAudioSession.sharedInstance()
        
        // Configure the audio session to use the device's microphone
        audioSession.requestLegacyPowerForNewMusicPlaybackEnabled(true)
        let category: AVAudioSession.Category = .record
        audioSession.setCategory(category, options: .notifyOthersOnDeactivation)
        
        // Create an AVAudioInputNode object
        let microphone = AVAudioInputNode()
        microphone.installTapOnBus(_:_self, bus: 0)
        
        // Set up a callback function that will be called whenever new audio data is available
        microphoneTapOutput(microphone, buffer: AVAudioPCMBuffer(pcmFormat: .float64, channelsPerPixel: 1), sampleTime: 0.0)
    }
    
    func microphoneTapOutput(_ node: AVAudioInputNode, _ buffer: AVAudioPCMBuffer, sampleTime: TimeInterval) {
        // Process the new audio data here
        
        // Create an output audio stream
        let outputAudioStream = AVAudioStreamPlayerNode(streamPlayerNode: AVAudioStreamerPlayerNode(node: node))
        
        // Prepare the player to play
        outputAudioStream.prepareToPlay()
        
        // Play the audio
        outputAudioStream.play()
    }
}

Conclusion

In this article, we went over how to capture and play back audio from a microphone in real-time using Swift for iOS development. We covered the basics of AVFoundation, including audio streams, audio buffers, and AVAudioSession.

We also went over how to set up an audio session to use the device’s microphone, capture audio from the microphone, process the new audio data, add it to the output audio stream, and play back the audio.

By following this article, you should now have a good understanding of how to work with audio on iOS devices using Swift.

Last modified on 2023-06-14