harmony 鸿蒙Audio Rendering Development

2022-08-09
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Audio Rendering Development

Introduction

AudioRenderer provides APIs for rendering audio files and controlling playback. It also supports audio interruption. You can use the APIs provided by AudioRenderer to play audio files in output devices and manage playback tasks. Before calling the APIs, be familiar with the following terms:

Audio interruption: When an audio stream with a higher priority needs to be played, the audio renderer interrupts the stream with a lower priority. For example, if a call comes in when the user is listening to music, the music playback, which is the lower priority stream, is paused.
Status check: During application development, you are advised to use on(‘stateChange’) to subscribe to state changes of the AudioRenderer instance. This is because some operations can be performed only when the audio renderer is in a given state. If the application performs an operation when the audio renderer is not in the given state, the system may throw an exception or generate other undefined behavior.
Asynchronous operation: To prevent the UI thread from being blocked, most AudioRenderer calls are asynchronous. Each API provides the callback and promise functions. The following examples use the promise functions. For more information, see AudioRenderer in Audio Management.
Audio interruption mode: OpenHarmony provides two audio interruption modes: shared mode and independent mode. In shared mode, all AudioRenderer instances created by the same application share one focus object, and there is no focus transfer inside the application. Therefore, no callback will be triggered. In independent mode, each AudioRenderer instance has an independent focus object, and focus transfer is triggered by focus preemption. When focus transfer occurs, the AudioRenderer instance that is having the focus receives a notification through the callback. By default, the shared mode is used. You can call setInterruptMode() to switch to the independent mode.

Working Principles

The following figure shows the audio renderer state transitions.

Figure 1 Audio renderer state transitions

audio-renderer-state

PREPARED: The audio renderer enters this state by calling create().
RUNNING: The audio renderer enters this state by calling start() when it is in the PREPARED state or by calling start() when it is in the STOPPED state.
PAUSED: The audio renderer enters this state by calling pause() when it is in the RUNNING state. When the audio playback is paused, it can call start() to resume the playback.
STOPPED: The audio renderer enters this state by calling stop() when it is in the PAUSED or RUNNING state.
RELEASED: The audio renderer enters this state by calling release() when it is in the PREPARED, PAUSED, or STOPPED state. In this state, the audio renderer releases all occupied hardware and software resources and will not transit to any other state.

How to Develop

For details about the APIs, see AudioRenderer in Audio Management.

Use createAudioRenderer() to create an AudioRenderer instance.

Set parameters of the AudioRenderer instance in audioRendererOptions. This instance is used to render audio, control and obtain the rendering status, and register a callback for notification.

 import audio from '@ohos.multimedia.audio';
   
    let audioStreamInfo = {
        samplingRate: audio.AudioSamplingRate.SAMPLE_RATE_44100,
        channels: audio.AudioChannel.CHANNEL_1,
        sampleFormat: audio.AudioSampleFormat.SAMPLE_FORMAT_S16LE,
        encodingType: audio.AudioEncodingType.ENCODING_TYPE_RAW
    }
    let audioRendererInfo = {
        content: audio.ContentType.CONTENT_TYPE_SPEECH,
        usage: audio.StreamUsage.STREAM_USAGE_VOICE_COMMUNICATION,
        rendererFlags: 0 // 0 is the extended flag bit of the audio renderer. The default value is 0.
    }
    let audioRendererOptions = {
        streamInfo: audioStreamInfo,
        rendererInfo: audioRendererInfo
 }
   
    let audioRenderer = await audio.createAudioRenderer(audioRendererOptions);
    console.log("Create audio renderer success.");

Use start() to start audio rendering.

   async function startRenderer() {
     let state = audioRenderer.state;
     // The audio renderer should be in the STATE_PREPARED, STATE_PAUSED, or STATE_STOPPED state when start() is called.
     if (state != audio.AudioState.STATE_PREPARED && state != audio.AudioState.STATE_PAUSED &&
       state != audio.AudioState.STATE_STOPPED) {
       console.info('Renderer is not in a correct state to start');
       return;
     }
   
     await audioRenderer.start();
   
     state = audioRenderer.state;
     if (state == audio.AudioState.STATE_RUNNING) {
       console.info('Renderer started');
     } else {
       console.error('Renderer start failed');
     }
   }

The renderer state will be STATE_RUNNING once the audio renderer is started. The application can then begin reading buffers.

Call write() to write data to the buffer.

Read the audio data to be played to the buffer. Call write() repeatedly to write the data to the buffer.

   import fileio from '@ohos.fileio';
   import audio from '@ohos.multimedia.audio';

   async function writeBuffer(buf) {
     // The write operation can be performed only when the state is STATE_RUNNING.
     if (audioRenderer.state != audio.AudioState.STATE_RUNNING) {
       console.error('Renderer is not running, do not write');
       return;
     }
     let writtenbytes = await audioRenderer.write(buf);
     console.info(`Actual written bytes: ${writtenbytes} `);
     if (writtenbytes < 0) {
       console.error('Write buffer failed. check the state of renderer');
     }
   }
    
   // Set a proper buffer size for the audio renderer. You can also select a buffer of another size.
   const bufferSize = await audioRenderer.getBufferSize();
   let dir = globalThis.fileDir; // You must use the sandbox path.
   const path = dir + '/file_example_WAV_2MG.wav'; // The file to render is in the following path: /data/storage/el2/base/haps/entry/files/file_example_WAV_2MG.wav
   console.info(`file path: ${ path}`);
   let ss = fileio.createStreamSync(path, 'r');
   const totalSize = fileio.statSync(path).size; // Size of the file to render.
   let discardHeader = new ArrayBuffer(bufferSize);
   ss.readSync(discardHeader);
   let rlen = 0;
   rlen += bufferSize;
    
   let id = setInterval(() => {
     if (audioRenderer.state == audio.AudioState.STATE_RELEASED) { // The rendering stops if the audio renderer is in the STATE_RELEASED state.
       ss.closeSync();
       await audioRenderer.stop();
       clearInterval(id);
     }
     if (audioRenderer.state == audio.AudioState.STATE_RUNNING) {
       if (rlen >= totalSize) { // The rendering stops if the file finishes reading.
         ss.closeSync();
         await audioRenderer.stop();
         clearInterval(id);
       }
       let buf = new ArrayBuffer(bufferSize);
       rlen += ss.readSync(buf);
       console.info(`Total bytes read from file: ${rlen}`);
       writeBuffer(buf);
     } else {
       console.info('check after next interval');
     }
   }, 30); // The timer interval is set based on the audio format. The unit is millisecond.

(Optional) Call pause() or stop() to pause or stop rendering.

    async function pauseRenderer() {
      let state = audioRenderer.state;
      // The audio renderer can be paused only when it is in the STATE_RUNNING state.
      if (state != audio.AudioState.STATE_RUNNING) {
        console.info('Renderer is not running');
        return;
      }

      await audioRenderer.pause();

      state = audioRenderer.state;
      if (state == audio.AudioState.STATE_PAUSED) {
        console.info('Renderer paused');
      } else {
        console.error('Renderer pause failed');
      }
    }

    async function stopRenderer() {
      let state = audioRenderer.state;
      // The audio renderer can be stopped only when it is in STATE_RUNNING or STATE_PAUSED state.
      if (state != audio.AudioState.STATE_RUNNING && state != audio.AudioState.STATE_PAUSED) {
        console.info('Renderer is not running or paused');
        return;
      }

      await audioRenderer.stop();

      state = audioRenderer.state;
      if (state == audio.AudioState.STATE_STOPPED) {
        console.info('Renderer stopped');
      } else {
        console.error('Renderer stop failed');
      }
    }

(Optional) Call drain() to clear the buffer.

    async function drainRenderer() {
      let state = audioRenderer.state;
      // drain() can be used only when the audio renderer is in the STATE_RUNNING state.
      if (state != audio.AudioState.STATE_RUNNING) {
        console.info('Renderer is not running');
        return;
      }

      await audioRenderer.drain();

      state = audioRenderer.state;
    }

After the task is complete, call release() to release related resources.

AudioRenderer uses a large number of system resources. Therefore, ensure that the resources are released after the task is complete.

    async function releaseRenderer() {
      let state = audioRenderer.state;
      // The audio renderer can be released only when it is not in the STATE_RELEASED or STATE_NEW state.
      if (state == audio.AudioState.STATE_RELEASED||state == audio.AudioState.STATE_NEW) {
        console.info('Renderer already released');
        return;
      }

      await audioRenderer.release();

      state = audioRenderer.state;
      if (state == audio.AudioState.STATE_RELEASED) {
        console.info('Renderer released');
      } else {
        console.info('Renderer release failed');
      }
    }

(Optional) Obtain the audio renderer information.

You can use the following code to obtain the audio renderer information:

   // Obtain the audio renderer state.
   let state = audioRenderer.state;
   
   // Obtain the audio renderer information.
   let audioRendererInfo : audio.AudioRendererInfo = await audioRenderer.getRendererInfo();

   // Obtain the audio stream information.
   let audioStreamInfo : audio.AudioStreamInfo = await audioRenderer.getStreamInfo();

   // Obtain the audio stream ID.
   let audioStreamId : number = await audioRenderer.getAudioStreamId();

   // Obtain the Unix timestamp, in nanoseconds.
   let audioTime : number = await audioRenderer.getAudioTime();

   // Obtain a proper minimum buffer size.
   let bufferSize : number = await audioRenderer.getBuffersize();

   // Obtain the audio renderer rate.
   let renderRate : audio.AudioRendererRate = await audioRenderer.getRenderRate();

(Optional) Set the audio renderer information.

You can use the following code to set the audio renderer information:

   // Set the audio renderer rate to RENDER_RATE_NORMAL.
   let renderRate : audio.AudioRendererRate = audio.AudioRendererRate.RENDER_RATE_NORMAL;
   await audioRenderer.setRenderRate(renderRate);

   // Set the interruption mode of the audio renderer to SHARE_MODE.
   let interruptMode : audio.InterruptMode = audio.InterruptMode.SHARE_MODE;
   await audioRenderer.setInterruptMode(interruptMode);

   // Set the volume of the stream to 0.5.
   let volume : number = 0.5;
   await audioRenderer.setVolume(volume);

(Optional) Use on(‘audioInterrupt’) to subscribe to the audio interruption event, and use off(‘audioInterrupt’) to unsubscribe from the event.

Audio interruption means that Stream A will be interrupted when Stream B with a higher or equal priority requests to become active and use the output device.

In some cases, the audio renderer performs forcible operations such as pausing and ducking, and notifies the application through InterruptEvent. In other cases, the application can choose to act on the InterruptEvent or ignore it.

In the case of audio interruption, the application may encounter write failures. To avoid such failures, interruption-unaware applications can use audioRenderer.state to check the audio renderer state before writing audio data. The applications can obtain more details by subscribing to the audio interruption events. For details, see InterruptEvent.

It should be noted that the audio interruption event subscription of the AudioRenderer module is slightly different from on(‘interrupt’) in AudioManager. The on(‘interrupt’) and off(‘interrupt’) APIs are deprecated since API version 9. In the AudioRenderer module, you only need to call on(‘audioInterrupt’) to listen for focus change events. When the AudioRenderer instance created by the application performs actions such as start, stop, and pause, it requests the focus, which triggers focus transfer and in return enables the related AudioRenderer instance to receive a notification through the callback. For instances other than AudioRenderer, such as frequency modulation (FM) and voice wakeup, the application does not create an instance. In this case, the application can call on(‘interrupt’) in AudioManager to receive a focus change notification.

   audioRenderer.on('audioInterrupt', (interruptEvent) => {
     console.info('InterruptEvent Received');
     console.info(`InterruptType: ${interruptEvent.eventType}`);
     console.info(`InterruptForceType: ${interruptEvent.forceType}`);
     console.info(`AInterruptHint: ${interruptEvent.hintType}`);

     if (interruptEvent.forceType == audio.InterruptForceType.INTERRUPT_FORCE) {
       switch (interruptEvent.hintType) {
         // Forcible pausing initiated by the audio framework. To prevent data loss, stop the write operation.
         case audio.InterruptHint.INTERRUPT_HINT_PAUSE:
           isPlay = false;
           break;
         // Forcible stopping initiated by the audio framework. To prevent data loss, stop the write operation.
         case audio.InterruptHint.INTERRUPT_HINT_STOP:
           isPlay = false;
           break;
         // Forcible ducking initiated by the audio framework.
         case audio.InterruptHint.INTERRUPT_HINT_DUCK:
           break;
         // Undocking initiated by the audio framework.
         case audio.InterruptHint.INTERRUPT_HINT_UNDUCK:
           break;
       }
     } else if (interruptEvent.forceType == audio.InterruptForceType.INTERRUPT_SHARE) {
       switch (interruptEvent.hintType) {
         // Notify the application that the rendering starts.
         case audio.InterruptHint.INTERRUPT_HINT_RESUME:
           startRenderer();
           break;
         // Notify the application that the audio stream is interrupted. The application then determines whether to continue. (In this example, the application pauses the rendering.)
         case audio.InterruptHint.INTERRUPT_HINT_PAUSE:
           isPlay = false;
           pauseRenderer();
           break;
       }
     }
   });

   audioRenderer.off('audioInterrupt'); // Unsubscribe from the audio interruption event. This event will no longer be listened for.

(Optional) Use on(‘markReach’) to subscribe to the mark reached event, and use off(‘markReach’) to unsubscribe from the event.

After the mark reached event is subscribed to, when the number of frames rendered by the audio renderer reaches the specified value, a callback is triggered and the specified value is returned.
```
audioRenderer.on('markReach', (reachNumber) => {
  console.info('Mark reach event Received');
  console.info(`The renderer reached frame: ${reachNumber}`);
});


audioRenderer.off('markReach'); // Unsubscribe from the mark reached event. This event will no longer be listened for.
```
(Optional) Use on(‘periodReach’) to subscribe to the period reached event, and use off(‘periodReach’) to unsubscribe from the event.

After the period reached event is subscribed to, each time the number of frames rendered by the audio renderer reaches the specified value, a callback is triggered and the specified value is returned.
```
audioRenderer.on('periodReach', (reachNumber) => {
  console.info('Period reach event Received');
  console.info(`In this period, the renderer reached frame: ${reachNumber} `);
});


audioRenderer.off('periodReach'); // Unsubscribe from the period reached event. This event will no longer be listened for.
```
(Optional) Use on(‘stateChange’) to subscribe to audio renderer state changes.

After the stateChange event is subscribed to, when the audio renderer state changes, a callback is triggered and the audio renderer state is returned.
```
audioRenderer.on('stateChange', (audioState) => {
  console.info('State change event Received');
  console.info(`Current renderer state is: ${audioState}`);
});
```

(Optional) Handle exceptions of on().

If the string or the parameter type passed in on() is incorrect , the application throws an exception. In this case, you can use try catch to capture the exception.

try {
  audioRenderer.on('invalidInput', () => { // The string is invalid.
  })
} catch (err) {
  console.info(`Call on function error, ${err}`); // The application throws exception 401.
}
try {
  audioRenderer.on(1, () => { // The type of the input parameter is incorrect.
  })
} catch (err) {
  console.info(`Call on function error,  ${err}`); // The application throws exception 6800101.
}

(Optional) Refer to the complete example of on(‘audioInterrupt’).

Create AudioRender1 and AudioRender2 in an application, configure the independent interruption mode, and call on(‘audioInterrupt’) to subscribe to audio interruption events. At the beginning, AudioRender1 has the focus. When AudioRender2 attempts to obtain the focus, AudioRender1 receives a focus transfer notification and the related log information is printed. If the shared mode is used, the log information will not be printed during application running.

 async runningAudioRender1(){
   let audioStreamInfo = {
     samplingRate: audio.AudioSamplingRate.SAMPLE_RATE_48000,
     channels: audio.AudioChannel.CHANNEL_1,
     sampleFormat: audio.AudioSampleFormat.SAMPLE_FORMAT_S32LE,
     encodingType: audio.AudioEncodingType.ENCODING_TYPE_RAW
   }
   let audioRendererInfo = {
     content: audio.ContentType.CONTENT_TYPE_MUSIC,
     usage: audio.StreamUsage.STREAM_USAGE_MEDIA,
     rendererFlags: 0 // 0 is the extended flag bit of the audio renderer. The default value is 0.
   }
   let audioRendererOptions = {
     streamInfo: audioStreamInfo,
 rendererInfo: audioRendererInfo
   }


   // 1.1 Create an instance.
  audioRenderer1 = await audio.createAudioRenderer(audioRendererOptions);
   console.info("Create audio renderer 1 success.");


   // 1.2 Set the independent mode.
   audioRenderer1.setInterruptMode(1).then( data => {
     console.info('audioRenderer1 setInterruptMode Success!');
   }).catch((err) => {
 console.error(`audioRenderer1 setInterruptMode Fail: ${err}`);
   });


   // 1.3 Set the listener.
   audioRenderer1.on('audioInterrupt', async(interruptEvent) => {
 console.info(`audioRenderer1 on audioInterrupt : ${JSON.stringify(interruptEvent)}`)
   });


   // 1.4 Start rendering.
  await audioRenderer1.start();
   console.info('startAudioRender1 success');


   // 1.5 Obtain the buffer size, which is the proper minimum buffer size of the audio renderer. You can also select a buffer of another size.
  const bufferSize = await audioRenderer1.getBufferSize();
   console.info(`audio bufferSize: ${bufferSize}`);


   // 1.6 Obtain the original audio data file.
   let dir = globalThis.fileDir; // You must use the sandbox path.
   const path1 = dir + '/music001_48000_32_1.wav'; // The file to render is in the following path: /data/storage/el2/base/haps/entry/files/music001_48000_32_1.wav
   console.info(`audioRender1 file path: ${ path1}`);
   let ss1 = await fileio.createStream(path1,'r');
   const totalSize1 = fileio.statSync(path1).size; // Size of the file to render.
   console.info(`totalSize1   -------: ${totalSize1}`);
   let discardHeader = new ArrayBuffer(bufferSize);
   ss1.readSync(discardHeader);
  let rlen = 0;
   rlen += bufferSize;


   // 1.7 Render the original audio data in the buffer by using audioRender.
   let id = setInterval(async () => {
     if (audioRenderer1.state == audio.AudioState.STATE_RELEASED) { // The rendering stops if the audio renderer is in the STATE_RELEASED state.
       ss1.closeSync();
       audioRenderer1.stop();
       clearInterval(id);
     }
     if (audioRenderer1.state == audio.AudioState.STATE_RUNNING) {
       if (rlen >= totalSize1) { // The rendering stops if the file finishes reading.
         ss1.closeSync();
         await audioRenderer1.stop();
         clearInterval(id);
       }
       let buf = new ArrayBuffer(bufferSize);
       rlen += ss1.readSync(buf);
       console.info(`Total bytes read from file: ${rlen}`);
       await writeBuffer(buf, that.audioRenderer1);
     } else {
       console.info('check after next interval');
     }
  }, 30); // The timer interval is set based on the audio format. The unit is millisecond.
 }


 async runningAudioRender2(){
   let audioStreamInfo = {
     samplingRate: audio.AudioSamplingRate.SAMPLE_RATE_48000,
     channels: audio.AudioChannel.CHANNEL_1,
     sampleFormat: audio.AudioSampleFormat.SAMPLE_FORMAT_S32LE,
     encodingType: audio.AudioEncodingType.ENCODING_TYPE_RAW
   }
   let audioRendererInfo = {
     content: audio.ContentType.CONTENT_TYPE_MUSIC,
     usage: audio.StreamUsage.STREAM_USAGE_MEDIA,
     rendererFlags: 0 // 0 is the extended flag bit of the audio renderer. The default value is 0.
   }
   let audioRendererOptions = {
     streamInfo: audioStreamInfo,
 rendererInfo: audioRendererInfo
   }


   // 2.1 Create another instance.
  audioRenderer2 = await audio.createAudioRenderer(audioRendererOptions);
   console.info("Create audio renderer 2 success.");


   // 2.2 Set the independent mode.
   audioRenderer2.setInterruptMode(1).then( data => {
     console.info('audioRenderer2 setInterruptMode Success!');
   }).catch((err) => {
 console.error(`audioRenderer2 setInterruptMode Fail: ${err}`);
   });


   // 2.3 Set the listener.
   audioRenderer2.on('audioInterrupt', async(interruptEvent) => {
 console.info(`audioRenderer2 on audioInterrupt : ${JSON.stringify(interruptEvent)}`)
   });


   // 2.4 Start rendering.
  await audioRenderer2.start();
   console.info('startAudioRender2 success');


   // 2.5 Obtain the buffer size.
  const bufferSize = await audioRenderer2.getBufferSize();
   console.info(`audio bufferSize: ${bufferSize}`);


   // 2.6 Read the original audio data file.
   let dir = globalThis.fileDir; // You must use the sandbox path.
   const path2 = dir + '/music002_48000_32_1.wav'; // The file to render is in the following path: /data/storage/el2/base/haps/entry/files/music002_48000_32_1.wav
   console.error(`audioRender1 file path: ${ path2}`);
   let ss2 = await fileio.createStream(path2,'r');
   const totalSize2 = fileio.statSync(path2).size; // Size of the file to render.
   console.error(`totalSize2   -------: ${totalSize2}`);
   let discardHeader2 = new ArrayBuffer(bufferSize);
   ss2.readSync(discardHeader2);
  let rlen = 0;
   rlen += bufferSize;


   // 2.7 Render the original audio data in the buffer by using audioRender.
   let id = setInterval(async () => {
     if (audioRenderer2.state == audio.AudioState.STATE_RELEASED) { // The rendering stops if the audio renderer is in the STATE_RELEASED state.
       ss2.closeSync();
       that.audioRenderer2.stop();
       clearInterval(id);
     }
     if (audioRenderer1.state == audio.AudioState.STATE_RUNNING) {
       if (rlen >= totalSize2) { // The rendering stops if the file finishes reading.
         ss2.closeSync();
         await audioRenderer2.stop();
         clearInterval(id);
       }
       let buf = new ArrayBuffer(bufferSize);
       rlen += ss2.readSync(buf);
       console.info(`Total bytes read from file: ${rlen}`);
       await writeBuffer(buf, that.audioRenderer2);
     } else {
       console.info('check after next interval');
     }
  }, 30); // The timer interval is set based on the audio format. The unit is millisecond.
 }


 async writeBuffer(buf, audioRender) {
   let writtenbytes;
   await audioRender.write(buf).then((value) => {
     writtenbytes = value;
     console.info(`Actual written bytes: ${writtenbytes} `);
   });
   if (typeof(writtenbytes) != 'number'||writtenbytes < 0) {
     console.error('get Write buffer failed. check the state of renderer');
  }
 }


 // Integrated invoking entry.
 async test(){
   await runningAudioRender1();
  await runningAudioRender2();
 }