OpenHarmony音频采集开发

1、OpenHarmony音频采集开发简介

AudioCapturer提供了用于获取原始音频文件的方法。开发者可以通过本博文了解应用如何通过AudioCapturer接口的调用实现音频数据的采集。

状态检查：在进行应用开发的过程中，建议开发者通过on('stateChange')方法订阅AudioCapturer的状态变更。因为针对AudioCapturer的某些操作，仅在音频采集器在固定状态时才能执行。如果应用在音频采集器处于错误状态时执行操作，系统可能会抛出异常或生成其他未定义的行为。

2、OpenHarmony音频采集运行机制

该模块提供了音频采集模块的状态变化示意图。

图1 音频采集状态变化示意图

PREPARED状态：通过调用create()方法进入到该状态。

RUNNING状态：正在进行音频数据播放，可以在prepared状态通过调用start()方法进入此状态，也可以在stopped状态通过调用start()方法进入此状态。

STOPPED状态：在running状态可以通过stop()方法停止音频数据的播放。

RELEASED状态：在prepared和stop状态，用户均可通过release()方法释放掉所有占用的硬件和软件资源，并且不会再进入到其他的任何一种状态了。

3、OpenHarmony音频采集的约束与限制

开发者在进行音频数据采集功能开发前，需要先对所开发的应用配置麦克风权限（ohos.permission.MICROPHONE），配置方式请参见访问控制授权申请。

4、OpenHarmony音频采集开发指导

详细API含义可参考：音频管理API文档AudioCapturer

(1).使用createAudioCapturer()创建一个AudioCapturer实例。

在audioCapturerOptions中设置音频采集器的相关参数。该实例可用于音频采集、控制和获取采集状态，以及注册通知回调。

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 audioCapturerInfo = {
  source: audio.SourceType.SOURCE_TYPE_MIC,
  capturerFlags: 0 // 0是音频采集器的扩展标志位，默认为0
}

let audioCapturerOptions = {
  streamInfo: audioStreamInfo,
  capturerInfo: audioCapturerInfo
}

let audioCapturer = await audio.createAudioCapturer(audioCapturerOptions);
console.log('AudioRecLog: Create audio capturer success.');

(2).调用start()方法来启动/恢复采集任务。

启动完成后，采集器状态将变更为STATE_RUNNING，然后应用可以开始读取缓冲区。

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

async function startCapturer() {
  let state = audioCapturer.state;
  // Capturer start时的状态应该是STATE_PREPARED、STATE_PAUSED和STATE_STOPPED之一.
  if (state != audio.AudioState.STATE_PREPARED || state != audio.AudioState.STATE_PAUSED ||
    state != audio.AudioState.STATE_STOPPED) {
    console.info('Capturer is not in a correct state to start');
    return;
  }
  await audioCapturer.start();

  state = audioCapturer.state;
  if (state == audio.AudioState.STATE_RUNNING) {
    console.info('AudioRecLog: Capturer started');
  } else {
    console.error('AudioRecLog: Capturer start failed');
  }
}

(3).读取采集器的音频数据并将其转换为字节流。重复调用read()方法读取数据，直到应用准备停止采集。

参考以下示例，将采集到的数据写入文件。

import fs from '@ohos.file.fs';

 let state = audioCapturer.state;
 // 只有状态为STATE_RUNNING的时候才可以read.
 if (state != audio.AudioState.STATE_RUNNING) {
   console.info('Capturer is not in a correct state to read');
   return;
 }
   
const path = '/data/data/.pulse_dir/capture_js.wav'; // 采集到的音频文件存储路径
let file = fs.openSync(filePath, 0o2);
let fd = file.fd;
if (file !== null) {
  console.info('AudioRecLog: file created');
} else {
  console.info('AudioRecLog: file create : FAILED');
  return;
}

if (fd !== null) {
  console.info('AudioRecLog: file fd opened in append mode');
}
   
let numBuffersToCapture = 150; // 循环写入150次
let count = 0;
while (numBuffersToCapture) {
  let bufferSize = await audioCapturer.getBufferSize();
  let buffer = await audioCapturer.read(bufferSize, true);
  let options = {
    offset: count * this.bufferSize,
    length: this.bufferSize
  }
  if (typeof(buffer) == undefined) {
    console.info('AudioRecLog: read buffer failed');
  } else {
    let number = fs.writeSync(fd, buffer, options);
    console.info(`AudioRecLog: data written: ${number}`);
  } 
  numBuffersToCapture--;
  count++;
}

(4).采集完成后，调用stop方法，停止录制。

 async function StopCapturer() {
   let state = audioCapturer.state;
   // 只有采集器状态为STATE_RUNNING或STATE_PAUSED的时候才可以停止
   if (state != audio.AudioState.STATE_RUNNING && state != audio.AudioState.STATE_PAUSED) {
     console.info('AudioRecLog: Capturer is not running or paused');
     return;
   }

   await audioCapturer.stop();

   state = audioCapturer.state;
   if (state == audio.AudioState.STATE_STOPPED) {
     console.info('AudioRecLog: Capturer stopped');
   } else {
     console.error('AudioRecLog: Capturer stop failed');
   }
 }

(5).任务结束，调用release()方法释放相关资源。

 async function releaseCapturer() {
   let state = audioCapturer.state;
   // 采集器状态不是STATE_RELEASED或STATE_NEW状态，才能release
   if (state == audio.AudioState.STATE_RELEASED || state == audio.AudioState.STATE_NEW) {
     console.info('AudioRecLog: Capturer already released');
     return;
   }

   await audioCapturer.release();

   state = audioCapturer.state;
   if (state == audio.AudioState.STATE_RELEASED) {
     console.info('AudioRecLog: Capturer released');
   } else {
     console.info('AudioRecLog: Capturer release failed');
   }
 }

(6).获取采集器相关信息

通过以下代码，可以获取采集器的相关信息。

// 获取当前采集器状态
let state = audioCapturer.state;

// 获取采集器信息
let audioCapturerInfo : audio.AuduioCapturerInfo = await audioCapturer.getCapturerInfo();

// 获取音频流信息
let audioStreamInfo : audio.AudioStreamInfo = await audioCapturer.getStreamInfo();

// 获取音频流ID
let audioStreamId : number = await audioCapturer.getAudioStreamId();

// 获取纳秒形式的Unix时间戳
let audioTime : number = await audioCapturer.getAudioTime();

// 获取合理的最小缓冲区大小
let bufferSize : number = await audioCapturer.getBufferSize();

(7).使用on('markReach')方法订阅采集器标记到达事件，使用off('markReach')取消订阅事件。

注册markReach监听后，当采集器采集的帧数到达设定值时，会触发回调并返回设定的值。

audioCapturer.on('markReach', (reachNumber) => {
  console.info('Mark reach event Received');
  console.info(`The Capturer reached frame: ${reachNumber}`);
});

audioCapturer.off('markReach'); // 取消markReach事件的订阅，后续将无法监听到“标记到达”事件

(8).使用on('periodReach')方法订阅采集器区间标记到达事件，使用off('periodReach')取消订阅事件。

注册periodReach监听后，每当采集器采集的帧数到达设定值时，会触发回调并返回设定的值。

audioCapturer.on('periodReach', (reachNumber) => {
  console.info('Period reach event Received');
  console.info(`In this period, the Capturer reached frame: ${reachNumber}`);
});

audioCapturer.off('periodReach'); // 取消periodReach事件的订阅，后续将无法监听到“区间标记到达”事件

(9).如果应用需要在采集器状态更新时进行一些操作，可以订阅该事件，当采集器状态更新时，会受到一个包含有事件类型的回调。

audioCapturer.on('stateChange', (state) => {
  console.info(`AudioCapturerLog: Changed State to : ${state}`)
  switch (state) {
    case audio.AudioState.STATE_PREPARED:
      console.info('--------CHANGE IN AUDIO STATE----------PREPARED--------------');
      console.info('Audio State is : Prepared');
      break;
    case audio.AudioState.STATE_RUNNING:
      console.info('--------CHANGE IN AUDIO STATE----------RUNNING--------------');
      console.info('Audio State is : Running');
      break;
    case audio.AudioState.STATE_STOPPED:
      console.info('--------CHANGE IN AUDIO STATE----------STOPPED--------------');
      console.info('Audio State is : stopped');
      break;
    case audio.AudioState.STATE_RELEASED:
      console.info('--------CHANGE IN AUDIO STATE----------RELEASED--------------');
      console.info('Audio State is : released');
      break;
    default:
      console.info('--------CHANGE IN AUDIO STATE----------INVALID--------------');
      console.info('Audio State is : invalid');
      break;
  }
});

OpenHarmony音频采集开发

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