What Is the AudioManager in Android?

The AudioManager in Android is a system service that provides audio functionality and management of audio resources for applications. It allows apps to handle audio streams, control audio focus, adjust audio volume, manage audio routing and more. Understanding AudioManager is important for apps that play or record audio.

Some key capabilities provided by AudioManager include:

• Managing audio focus – This allows coordinated audio playback between apps so that only one app plays audio at a time.
• Volume control – Apps can adjust volume levels for music, notifications, system sounds etc.
• Routing audio to different outputs – Audio can be routed to speaker, headphones, Bluetooth etc.
• Applying audio effects like equalization and bass boost.
• Monitoring headphones connection state.
• Accessing audio session IDs.

With these features, AudioManager enables apps to deliver robust audio experiences in areas like media playback, voice calls, notifications and more. Understanding how to leverage AudioManager is an important skill for Android audio development.

Managing Audio Output

The AudioManager class in Android provides key capabilities for controlling audio output [1]. It allows apps to adjust volume, set audio focus, and route audio to different outputs like the speaker, headphones, or Bluetooth devices.

For volume control, the AudioManager has methods like setStreamVolume() to change the volume of a specific stream like music or notifications, and adjustStreamVolume() to relatively raise or lower the volume. Apps can also retrieve volume levels and register callbacks to be notified of volume changes.

Managing audio focus is critical so multiple apps don’t play audio simultaneously. The AudioManager has APIs like requestAudioFocus() and abandonAudioFocus() to acquire and release audio focus. It uses callbacks to notify apps when they gain or lose focus. Apps can duck their audio when losing focus.

The AudioManager allows routing audio to different outputs, like earpiece, speaker, wired headphones, Bluetooth etc. The setMode() method configures routing, while setSpeakerphoneOn() toggles the speakerphone. Apps can also check the current audio route with getRoutedDevice().

Managing Audio Input

The AudioManager class provides methods to manage audio input sources and control audio recording on Android devices. Some key capabilities for managing audio input include:

Selecting an audio input source – The AudioManager allows selecting between different audio input sources like the microphone, wired headset mic, or Bluetooth headset mic using the setMicrophoneMute() and setBluetoothScoOn() methods.

Initiating and stopping recording – The startRecording() and stopRecording() methods can start and stop recording from the selected audio input source. This allows recording audio from the microphone or other input.

Setting recording parameters – The setRecordingParams() method sets sample rate, channel config, audio encoding, etc. for the recording session. This allows optimizing audio quality.

Monitoring recording events – Methods like getActiveRecordingConfigurations() let apps monitor current recording state and configurations.

Overall, the AudioManager APIs allow complete control over audio input selection, recording, and monitoring on Android devices. This is critical for apps like voice recorders, speech interfaces, and audio messaging.

Audio Focus and Ducking

Audio focus refers to controlling which audio streams have priority when multiple apps try to play audio at the same time. The AudioManager allows apps to request audio focus with different priority levels. When an app requests focus, other lower priority audio streams will be “ducked”, meaning their volume will be lowered temporarily so the higher priority audio can be heard.

Apps can request audio focus by calling the requestAudioFocus() method, and passing in an AudioFocusRequest object specifying the focus parameters. There are 3 focus types – gain, gain transient, and gain transient may duck, with gain being the highest priority. Apps should request the minimum focus level needed to provide a good user experience.

When focus is abandoned or lost, the AudioManager will notify the app via an onAudioFocusChange() callback. This allows apps to pause/resume audio playback accordingly. Proper audio focus handling ensures minimal disruption for the user when multiple media apps are active.

For example, a music player would request permanent focus with gain type, while a game may request transient focus. This would duck the music when game sounds play, then return focus back to the music player when finished.¹

Audio Routing and Effects

The AudioManager allows you to control audio routing and apply audio effects in Android. You can connect to various audio devices like headsets, speakers, and Bluetooth devices. The AudioManager provides methods like setMode(), setRouting(), and setForceUse() to control where audio is routed.

For example, you can route audio to a wired headset using:

audioManager.setMode(AudioManager.MODE_IN_COMMUNICATION); 
audioManager.setRouting(AudioManager.MODE_IN_COMMUNICATION, AudioManager.ROUTE_WIRED_HEADSET, AudioManager.ROUTE_ALL);

To enable Bluetooth audio routing:

audioManager.startBluetoothSco();
audioManager.setBluetoothScoOn(true);

The AudioManager also allows applying audio effects like equalization, bass boost, and virtualization. You can use the setEffectsEnabled() method to enable/disable effects. For example:

audioManager.setEffectsEnabled(true); 
audioManager.setEqualizerEnabled(true);

This will enable the global audio effects and specifically the equalizer effect. The AudioManager provides flexible control over audio routing and effects in Android.

Playback APIs

Android provides several APIs for audio playback, the most common being MediaPlayer and SoundPool.

MediaPlayer is used for streaming and playing back audio files and streams. It supports common audio formats like MP3, AAC, OGG, and WAV, as well as adaptive streaming protocols like HLS and DASH. MediaPlayer provides a simple API for controlling playback and querying metadata.

SoundPool is optimized for low latency audio playback of short sound clips and sound effects. It allows you to load sounds into memory and playback with low latency. SoundPool is useful for games and user interface sounds that require quick response times.

In addition to MediaPlayer and SoundPool, Android also provides AudioTrack for low level PCM audio output, and the ToneGenerator class for generating simple tones and DTMF sounds. The ExoPlayer library built on top of MediaPlayer also offers advanced streaming capabilities.

Volume and Audio Settings

The AudioManager allows apps to adjust volume levels, respond to volume setting changes, and manage audio sessions.

To change the volume of a particular stream, such as music or alarms, you can call setStreamVolume() and pass the stream type and desired volume level. Apps should check the max volume for each stream before setting the level by calling getStreamMaxVolume(). Volume levels range from 0 to the max volume.

To be notified when volume levels change, apps can implement an OnAudioFocusChangeListener and override onVolumeChanged(). This method will be called whenever a registered stream’s volume is adjusted by the user or system.

Apps that play audio often need to manage audio focus and audio sessions. An app can request audio focus when it needs exclusive access to the audio system by calling requestAudioFocus(). This will pause other audio streams while the app plays its audio. The app should call abandonAudioFocus() when it is done to allow other apps to resume audio playback.

Finally, AudioManager provides methods like adjustStreamVolume(), setRingerMode(), and setSpeakerphoneOn() to control volume levels and audio routing programmatically.

Performance and Optimization

When working with audio in Android, it’s important to optimize your app for performance to provide the best user experience. High latency or laggy audio can frustrate users. Excessive resource usage can drain battery life. Testing thoroughly for audio issues is critical before launch.

To reduce latency, use the lowest audio buffer sizes possible without distortion or glitches. Smaller audio buffers reduce delay but require more consistent processing. Test with various buffer sizes to find the optimal balance for your app.

To minimize resource usage, release audio resources like AudioTrack objects when no longer needed. Avoid resource contention between audio and other processing. Use profiling tools like Systrace to identify potential bottlenecks.

Rigorously test audio functionality on a diverse range of devices. Confirm audio plays as expected and doesn’t glitch. Verify audio effects and routing work properly. Check that volume levels are appropriate.

Refer to the official Android developer documentation on audio optimization and performance measurements for more techniques.

Common Use Cases

The AudioManager class is commonly used for managing audio in key use cases like music/video playback, voice calls, accessibility features, and gaming audio. Here are some examples:

Music and Video Playback

Apps that play music or video often use AudioManager to handle audio focus requests and ducking, set audio volume, and route audio output to different devices like headphones or Bluetooth speakers. For example, a music app may request audio focus when a song starts playing and adjust the volume using setStreamVolume().

Voice Calls

The AudioManager can control routing and volume for voice calls made through the device. The Phone app might use setMode(MODE_IN_CALL) to optimize audio routing and settings during a call.

Accessibility

Accessibility services rely on AudioManager to play text-to-speech output for visually impaired users. The playSoundEffect() method can also be used for audio cues.

Gaming Audio

Games need to handle sound effects, background music, and audio focus changes as gameplay switches between activities. getMode() allows checking if a call or other audio is actively playing.

Best Practices

When using the AudioManager, there are some best practices to follow to avoid common pitfalls and use it effectively:

• Check audio focus – Before playing audio, check if your app has audio focus using AudioManager.requestAudioFocus(). This avoids interrupting other apps already using audio.
• Handle audio focus loss – Implement an AudioManager.OnAudioFocusChangeListener to handle losing focus gracefully by pausing playback.
• Minimize audio sessions – Use the minimum number of audio sessions needed, and reuse existing sessions when possible. Each session consumes system resources.
• Reset audio configurations – After using the AudioManager to change audio settings like speakerphone or Bluetooth routing, remember to reset the configurations when done.
• Avoid memory leaks – Make sure to release audio sessions and listeners when they are no longer needed to avoid resource leaks.
• Optimize for performance – Use audio streams and codecs optimized for background audio like STREAM_MUSIC to minimize battery impact.
• Handle headset events – Listen for headset plug events and pause playback accordingly when a headset is unplugged.

Following best practices for requesting focus, minimizing resource usage, and handling configuration changes will lead to robust audio handling in any Android app.