Raw audio processing

In some scenarios, raw audio captured through the microphone must be processed to achieve the desired functionality or to enhance the user experience. Voice SDK enables you to pre and post process the captured audio for implementation of custom playback effects.

You can use the raw data processing functionality in Voice SDK to process the feed according to your particular scenario. This feature enables you to pre-process the captured signal before sending it to the encoder, or to post-process the decoded signal before playback. To implement processing of raw audio data in your app, you take the following steps.

1. Setup an audio frame observer.
2. Register the audio frame observer before joining a channel.
3. Set the format of audio frames captured by each callback.
4. Implement callbacks in the frame observers to process raw audio data.
5. Unregister the frame observers before leaving a channel.

The figure below shows the workflow you need to implement to process raw audio data in your app.

To follow this procedure you must have implemented Get Started with Voice Calling.

To create the environment necessary to integrate raw audio processing in your app, open the Get Started with Voice Calling project you created previously.

When a user captures or receives audio data, the data is available to the app for processing before it is played. This section shows how to retrieve this data and process it, step-by-step.

This sections describes the steps required to use the relevant libraries, declare the necessary variables, and setup audio processing.

Import the required Android and Agora libraries

To integrate Video SDK frame observer libraries into your app, add the following statements after the last import statement in /app/java/com.example.<projectname>/MainActivity.

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import io.agora.rtc2.IAudioFrameObserver;

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import java.nio.ByteBuffer;

To register and use an audio frame observer in your app, take the following steps:

1. Setup the audio frame observer

   The IAudioFrameObserver gives you access to each audio frame after it is captured or before it is played back. To setup the IAudioFrameObserver, add the following lines to the MainActivity class after variable declarations:

   
   

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   private final IAudioFrameObserver iAudioFrameObserver = new IAudioFrameObserver() {

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   @Override

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   public boolean onRecordAudioFrame(String channelId, int type, int samplesPerChannel,

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   int bytesPerSample, int channels, int samplesPerSec, ByteBuffer buffer, long renderTimeMs, int avsync_type) {

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   // Gets the captured audio frame.

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   // Add code here to process the recorded audio

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   return false;

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   }

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   @Override

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   public boolean onPlaybackAudioFrame(String channelId, int type, int samplesPerChannel,

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   int bytesPerSample, int channels, int samplesPerSec, ByteBuffer buffer, long renderTimeMs, int avsync_type) {

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   // Gets the audio frame for playback.

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   // Add code here to process the playback audio

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   return false;

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   }

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   @Override

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   public boolean onMixedAudioFrame(String channelId, int type, int samplesPerChannel,

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   int bytesPerSample, int channels, int samplesPerSec, ByteBuffer buffer, long renderTimeMs, int avsync_type) {

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   // Retrieves the mixed captured and playback audio frame.

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   return false;

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   }

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   @Override

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   public boolean onPlaybackAudioFrameBeforeMixing(String channelId, int userId, int type, int samplesPerChannel,

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   int bytesPerSample, int channels, int samplesPerSec, ByteBuffer buffer, long renderTimeMs, int avsync_type) {

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   // Retrieves the audio frame of a specified user before mixing.

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   return false;

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   }

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   };

   
   

2. Register the audio frame observer

   To receive callbacks declared in IAudioFrameObserver, you must register the audio frame observer with the Agora Engine, before joining a channel . To specify the format of audio frames captured by each IAudioFrameObserver callback, use the setRecordingAudioFrameParameters, setMixedAudioFrameParameters and setPlaybackAudioFrameParameters methods. To do this, add the following lines before agoraEngine.joinChannel in the joinChannel() method:

   
   

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   agoraEngine.registerAudioFrameObserver(iAudioFrameObserver);

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   // Set the format of the captured raw audio data.

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   int SAMPLE_RATE = 16000, SAMPLE_NUM_OF_CHANNEL = 1, SAMPLES_PER_CALL = 1024;

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   agoraEngine.setRecordingAudioFrameParameters(SAMPLE_RATE, SAMPLE_NUM_OF_CHANNEL,

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   Constants.RAW_AUDIO_FRAME_OP_MODE_READ_WRITE,SAMPLES_PER_CALL);

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   agoraEngine.setPlaybackAudioFrameParameters(SAMPLE_RATE, SAMPLE_NUM_OF_CHANNEL,

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   Constants.RAW_AUDIO_FRAME_OP_MODE_READ_WRITE,SAMPLES_PER_CALL);

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   agoraEngine.setMixedAudioFrameParameters(SAMPLE_RATE, SAMPLE_NUM_OF_CHANNEL, SAMPLES_PER_CALL);

   
   

3. Unregister the audio observer when you leave a channel

   When you leave a channel, you unregister the frame observer by calling the register frame observer method again with a null argument. To do this, add the following lines to the 'joinLeaveChannel(View view)' method before agoraEngine.leaveChannel();:

   
   

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   agoraEngine.registerAudioFrameObserver(null);

   
   

To ensure that you have implemented raw data processing into your app:

1. Generate a temporary token in Agora Console .

2. In your browser, navigate to the Agora web demo and update App ID, Channel, and Token with the values for your temporary token, then click Join.

3. In Android Studio, open app/java/com.example.<projectname>/MainActivity, and update appId, channelName and token with the values for your temporary token.

4. Edit the iAudioFrameObserver definition to add code that processes the raw audio data you receive in the following callbacks

   • onRecordAudioFrame: Gets the captured audio frame data

   • onPlaybackAudioFrame: Gets the audio frame for playback

5. Connect a physical Android device to your development device.

6. In Android Studio, click Run app. A moment later you see the project installed on your device.

   If this is the first time you run the project, grant microphone access to your app.

7. Press Join to hear the processed audio feed from the web app.

This section contains information that completes the information in this page, or points you to documentation that explains other aspects to this product.

• IAudioFrameObserver
• registerAudioFrameObserver