# Custom audio source (/en/realtime-media/voice/build/customize-audio-processing/custom-audio/android)

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The default audio module of Voice SDK meets the need of using basic audio functions in your app. For adding advanced audio functions, Voice SDK supports using custom audio sources and custom audio rendering modules.

    Video SDK uses the basic audio module on the device your app runs on by default. However, there are certain use-cases where you want to integrate a custom audio source into your app, such as:

    * Your app has its own audio module.
    * You need to process the captured audio with a pre-processing library for audio enhancement.
    * You need flexible device resource allocation to avoid conflicts with other services.

    This page shows you how to capture and render audio from custom sources.

    ## Understand the tech [#understand-the-tech]

    To set an external audio source, you configure the Agora Engine before joining a channel. To manage the capture and processing of audio frames, you use methods from outside the Video SDK that are specific to your custom source. Video SDK enables you to push processed audio data to the subscribers in a channel.

    #### Capture custom audio [#capture-custom-audio]

    The following figure illustrates the process of custom audio capture.

    ![Audio data transmission](https://assets-docs.agora.io/images/video-sdk/audio-data-transmission.svg)

    * You implement the capture module using external methods provided by the SDK.

    * You call `pushExternalAudioFrame` to send the captured audio frames to the SDK.

    #### Render custom audio [#render-custom-audio]

    The following figure illustrates the process of custom audio rendering.

    ![Audio Data Transmission](https://assets-docs.agora.io/images/video-sdk/custom-audio-rendering-sdk.svg)

    * You implement the rendering module using external methods provided by the SDK.

    * You call `pullPlaybackAudioFrame` to retrieve the audio data sent by remote users.

    ## Prerequisites [#prerequisites]

    Ensure that you have implemented the [SDK quickstart](../index.mdx) in your project.

    ## Implementation [#implementation]

    This section shows you how to implement custom audio capture and render audio from a custom source.

    ### Custom audio capture [#custom-audio-capture]

    Refer to the following call sequence diagram to implement custom audio capture in your app:

    **Custom audio capture process**

    ![Custom audio capture](https://assets-docs.agora.io/images/video-sdk/custom-audio-capture-with-custom-track.svg)

    Follow these steps to implement custom audio capture in your project:

    1. After initializing `RtcEngine`, call `createCustomAudioTrack` to create a custom audio track and obtain the audio track ID.

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        ```java
        AudioTrackConfig config = new AudioTrackConfig();
          config.enableLocalPlayback = false;
          customAudioTrack = engine.createCustomAudioTrack(Constants.AudioTrackType.AUDIO_TRACK_MIXABLE, config);
        ```
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        ```kotlin
        val config = AudioTrackConfig().apply {
            enableLocalPlayback = false
          }
          customAudioTrack = engine.createCustomAudioTrack(Constants.AudioTrackType.AUDIO_TRACK_MIXABLE, config)
        ```
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    2. Call `joinChannel` to join the channel. In `ChannelMediaOptions`, set `publishCustomAudioTrackId` to the audio track ID obtained in step 1, and set `publishCustomAudioTrack` to `true` to publish the custom audio track.

       <CalloutContainer type="info">
         <CalloutDescription>
           To use `enableCustomAudioLocalPlayback` for local playback of an external audio source, or to adjust the volume of a custom audio track with `adjustCustomAudioPlayoutVolume`, set `enableAudioRecordingOrPlayout` to `true` in `ChannelMediaOptions`.
         </CalloutDescription>
       </CalloutContainer>

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        ```java
        ChannelMediaOptions option = new ChannelMediaOptions();
          option.clientRoleType = Constants.CLIENT_ROLE_BROADCASTER;
          option.autoSubscribeAudio = true;
          option.autoSubscribeVideo = true;
          // In the audio self-collection use-case, the audio collected by the microphone is not published
          option.publishMicrophoneTrack = false;
          // Publish the custom audio track
          publishCustomAudioTrack = true
          // Set the custom audio track ID
          publishCustomAudioTrackId = customAudioTrack

          // Join the channel
          val res = engine.joinChannel(accessToken, channelId, 0, option)
        ```
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        ```kotlin
        val option = ChannelMediaOptions().apply {
            clientRoleType = Constants.CLIENT_ROLE_BROADCASTER
            autoSubscribeAudio = true
            autoSubscribeVideo = true
            // In the audio self-collection use-case, the audio collected by the microphone is not published
            publishMicrophoneTrack = false
            // Publish the custom audio track
            publishCustomAudioTrack = true
            // Set the custom audio track ID
            publishCustomAudioTrackId = customAudioTrack
          }

          // Join the channel
          val res = engine.joinChannel(accessToken, channelId, 0, option)
        ```
      </CodeBlockTab>
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    3. Agora provides the [AudioFileReader.java](https://github.com/AgoraIO/API-Examples/blob/main/Android/APIExample/app/src/main/java/io/agora/api/example/utils/AudioFileReader.java) sample to demonstrate how to read and publish PCM-format audio data from a local file. In a production environment, you create a custom audio acquisition module based on your business needs.

    4. Call `pushExternalAudioFrame` to send the captured audio frame to the SDK through the custom audio track. Ensure that the `trackId` matches the audio track ID you obtained by calling `createCustomAudioTrack`. Set `sampleRate`, `channels`, and `bytesPerSample` to define the sampling rate, number of channels, and bytes per sample of the external audio frame.

       <CalloutContainer type="info">
         <CalloutDescription>
           For audio and video synchronization, Agora recommends calling `getCurrentMonotonicTimeInMs` to get the system’s current monotonic time and setting the `timestamp` accordingly.
         </CalloutDescription>
       </CalloutContainer>

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        ```java
        audioPushingHelper = new AudioFileReader(requireContext(), (buffer, timestamp) -> {
            if (joined && engine != null && customAudioTrack != -1) {
              // Push external audio frames to SDK
              int ret = engine.pushExternalAudioFrame(buffer, timestamp,
                  AudioFileReader.SAMPLE_RATE,
                  AudioFileReader.SAMPLE_NUM_OF_CHANNEL,
                  Constants.BytesPerSample.TWO_BYTES_PER_SAMPLE,
                  customAudioTrack);
              Log.i(TAG, "pushExternalAudioFrame times:" + (++\pushTimes) + ", ret=" + ret);
            }
          });
        ```
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        ```kotlin
        audioPushingHelper = AudioFileReader(requireContext()) { buffer, timestamp ->
            if (joined && engine != null && customAudioTrack != -1) {
              // Push external audio frames to SDK
              val ret = engine.pushExternalAudioFrame(
                buffer, timestamp,
                AudioFileReader.SAMPLE_RATE,
                AudioFileReader.SAMPLE_NUM_OF_CHANNEL,
                Constants.BytesPerSample.TWO_BYTES_PER_SAMPLE,
                customAudioTrack
              )
              Log.i(TAG, "pushExternalAudioFrame times: \${++pushTimes\}, ret=$ret")
            }
          }
        ```
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    5. To stop publishing custom audio, call `destroyCustomAudioTrack` to destroy the custom audio track.

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        ```java
        // Destroy the custom audio track
          engine.destroyCustomAudioTrack(customAudioTrack);
        ```
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        ```kotlin
        // Destroy the custom audio track
          engine.destroyCustomAudioTrack(customAudioTrack)
        ```
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    ### Custom audio rendering [#custom-audio-rendering]

    This section shows you how to implement custom audio rendering. Refer to the following call sequence diagram to implement custom audio rendering in your app:

    **Custom audio rendering workflow**

    ![Custom Audio Rendering Workflow](https://assets-docs.agora.io/images/video-sdk/custom-audio-render.svg)

    To implement custom audio rendering, use the following methods:

    1. Before calling `joinChannel`, use `setExternalAudioSink` to enable and configure custom audio rendering.

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        ```java
        rtcEngine.setExternalAudioSink(
            true,   // Enable custom audio rendering
            44100,   // Sampling rate (Hz). Set this value to 16000, 32000, 441000, or 48000
            1     // Number of channels for the custom audio source. Set this value to 1 or 2
          );
        ```
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      <CodeBlockTab value="kotlin">
        ```kotlin
        rtcEngine.setExternalAudioSink(
            true,   // Enable custom audio rendering
            44100,   // Sampling rate (Hz). Set this value to 16000, 32000, 441000, or 48000
            1     // Number of channels for the custom audio source. Set this value to 1 or 2
          )
        ```
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    2. After joining the channel, call `pullPlaybackAudioFrame` to get audio data sent by remote users. Use your own audio renderer to process the audio data and then play the rendered data.

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        ```java
        private class FileThread implements Runnable {

            @Override
            public void run() {
              while (mPull) {
                int lengthInByte = 48000 / 1000 * 2 * 1 * 10;
                ByteBuffer frame = ByteBuffer.allocateDirect(lengthInByte);
                int ret = engine.pullPlaybackAudioFrame(frame, lengthInByte);
                byte[] data = new byte[frame.remaining()];
                frame.get(data, 0, data.length);
                // Write to a local file or render using a player
                FileIOUtils.writeFileFromBytesByChannel("/sdcard/agora/pull_48k.pcm", data, true, true);
                try {
                  Thread.sleep(10);
                } catch (InterruptedException e) {
                  e.printStackTrace();
                }
              }
            }
          }
        ```
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        ```kotlin
        private class FileThread : Runnable {

            override fun run() {
              while (mPull) {
                val lengthInByte = 48000 / 1000 * 2 * 1 * 10
                val frame = ByteBuffer.allocateDirect(lengthInByte)
                val ret = engine.pullPlaybackAudioFrame(frame, lengthInByte)
                val data = ByteArray(frame.remaining())
                frame.get(data, 0, data.size)
                // Write to a local file or render using a player
                FileIOUtils.writeFileFromBytesByChannel("/sdcard/agora/pull_48k.pcm", data, true, true)
                try {
                  Thread.sleep(10)
                } catch (e: InterruptedException) {
                  e.printStackTrace()
                }
              }
            }
          }
        ```
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    ### Using raw audio data callback [#using-raw-audio-data-callback]

    This section explains how to implement custom audio rendering.

    To retrieve audio data for playback, implement collection and processing of raw audio data. Refer to [Raw audio processing](stream-raw-audio.mdx).

    Follow these steps to call the raw audio data API in your project for custom audio rendering:

    1. Retrieve audio data for playback using the `onRecordAudioFrame`, `onPlaybackAudioFrame`, `onMixedAudioFrame`, or `onPlaybackAudioFrameBeforeMixing` callback.

    2. Independently render and play the audio data.

    ## Reference [#reference]

    This section explains how to implement different sound effects and audio mixing in your app, covering essential steps and code snippets.

    ### Sample projects [#sample-projects]

    Agora provides the following open-source sample projects for audio self-capture and audio self-rendering for your reference:

    * [CustomAudioSource](https://github.com/AgoraIO/API-Examples/blob/main/Android/APIExample/app/src/main/java/io/agora/api/example/examples/advanced/customaudio/CustomAudioSource.java)
    * [CustomAudioRender](https://github.com/AgoraIO/API-Examples/blob/main/Android/APIExample/app/src/main/java/io/agora/api/example/examples/advanced/customaudio/CustomAudioRender.java)

    ### API reference [#api-reference]

    * [`createCustomAudioTrack`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_imediaengine.html#api_imediaengine_createcustomaudiotrack)

    * [`destroyCustomAudioTrack`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_imediaengine.html#api_imediaengine_destroycustomaudiotrack)

    * [`pushExternalAudioFrame`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_pushaudioframe2)

    * [`setExternalAudioSink`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_imediaengine_setexternalaudiosink)

    * [`pullPlaybackAudioFrame` \[1/2\]](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_imediaengine_pullaudioframe)

    * [`pullPlaybackAudioFrame` \[2/2\]](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_pullaudioframe2)