Android音視頻學習(二)

引用

感謝灰色飄零大佬的這篇指南

概念

Android提供了兩種音頻錄製方式, 這裏講比較底層一些的AudioRecord.

引用一下google的定義:

AudioRecord類管理Java程序的音頻資源, 以記錄來自音頻輸入硬件的音頻. 這是經過向AudioRecord對象讀取數據來實現的. 應用經過如下三種方法之一及時的查詢AudioRecord對象:

1. read(byte[], int, int)
2. read(short[], int, int)
3. read(ByteBuffer, int)

具體使用哪一個, 是根據音頻數據存儲格式自由選擇的. 建立後, AudioRecord對象初始化其關聯的音頻緩衝區, 它將填充新的音頻數據. 在構造期間指定的緩衝區大小決定了AudioRecord在"過分運行"時, 還沒有讀取的數據能夠保存多長時間. 所以從音頻硬件讀取的數據塊大小應該小於緩衝區大小.

下面是具體實現

權限申請

private void checkPermission() {
    //6.0之後須要動態申請權限
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
      //檢查是否已經獲取權限, 沒有獲取的權限放到list裏
      for (String permission : permissions) {
        if (ContextCompat.checkSelfPermission(this, permission)
            != PackageManager.PERMISSION_GRANTED) {
          mPermissionList.add(permission);
        }
      }

      //list不爲空, 就去申請所須要的權限
      if (!mPermissionList.isEmpty()) {
        String[] permissions = mPermissionList.toArray(new String[0]);
        ActivityCompat.requestPermissions(this, permissions, MY_PERMISSIONS_REQUEST);
      }
    }
  }
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建立AudioRecord

這裏寫了個方法來建立AudioRecord:

private void createAudioRecord() {
    //這裏經過AudioRecord類獲取最小的緩存大小
    recordBufSize =
        AudioRecord.getMinBufferSize(GlobalConfig.SAMPLE_RATE_INHZ, GlobalConfig.CHANNEL_CONFIG,
            GlobalConfig.AUDIO_FORMAT);
    mAudioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, GlobalConfig.SAMPLE_RATE_INHZ,
        GlobalConfig.CHANNEL_CONFIG, GlobalConfig.AUDIO_FORMAT, recordBufSize);
  }
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用到的配置類:

public class GlobalConfig {

  //採樣率
  public static final int SAMPLE_RATE_INHZ = 44100;

  //聲道
  public static final int CHANNEL_CONFIG = AudioFormat.CHANNEL_IN_MONO;

  //返回的音頻數據格式
  public static final int AUDIO_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
}
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開始錄製音頻

private void startRecord() {
    createAudioRecord();

    //buffer, 用來從AudioRecord中獲取錄製的音頻
    final byte[] data = new byte[recordBufSize];
    //pcm文件存儲位置
    final File file = new File(getExternalFilesDir(Environment.DIRECTORY_MUSIC), "test.pcm");
    if (!file.mkdirs()) {
      Log.d(TAG, "startRecord: " + "Directory not created");
    }
    if (file.exists()) {
      file.delete();
    }

    //開始錄製
    mAudioRecord.startRecording();
    //錄製標記
    isRecording = true;

    //不阻塞主線程
    new Thread(new Runnable() {
      @Override public void run() {
        //新建文件輸出流, 把錄製音頻存儲
        FileOutputStream fileOutputStream = null;
        try {
          fileOutputStream = new FileOutputStream(file);
        } catch (FileNotFoundException e) {
          e.printStackTrace();
        }

        if (fileOutputStream != null) {
          while (isRecording) {
            //將錄製音頻傳到buffer裏
            int read = mAudioRecord.read(data, 0, recordBufSize);
            if (read != AudioRecord.ERROR_INVALID_OPERATION) {
              try {
                //buffer數據沒問題寫入到文件中
                fileOutputStream.write(data);
              } catch (IOException e) {
                e.printStackTrace();
              }
            }
          }

          try {
            //不要忘記關文件輸出流
            fileOutputStream.close();
          } catch (IOException e) {
            e.printStackTrace();
          }
        }
      }
    }).start();
  }
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中止錄製

private void stopRecord() {
  //中止錄音
  isRecording = false;
  //不要泄露
  if (mAudioRecord != null) {
    mAudioRecord.stop();
    mAudioRecord.release();
    mAudioRecord = null;
  }
}
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原始音頻文件轉化

這裏直接給一個大佬提供的轉化工具類:

/** * 將pcm音頻文件轉換爲wav音頻文件 */
public class PcmToWavUtil {

    /** * 緩存的音頻大小 */
    private int mBufferSize;
    /** * 採樣率 */
    private int mSampleRate;
    /** * 聲道數 */
    private int mChannel;


    /** * @param sampleRate sample rate、採樣率 * @param channel channel、聲道 * @param encoding Audio data format、音頻格式 */
    PcmToWavUtil(int sampleRate, int channel, int encoding) {
        this.mSampleRate = sampleRate;
        this.mChannel = channel;
        this.mBufferSize = AudioRecord.getMinBufferSize(mSampleRate, mChannel, encoding);
    }


    /** * pcm文件轉wav文件 * * @param inFilename 源文件路徑 * @param outFilename 目標文件路徑 */
    public void pcmToWav(String inFilename, String outFilename) {
        FileInputStream in;
        FileOutputStream out;
        long totalAudioLen;
        long totalDataLen;
        long longSampleRate = mSampleRate;
        int channels = mChannel == AudioFormat.CHANNEL_IN_MONO ? 1 : 2;
        long byteRate = 16 * mSampleRate * channels / 8;
        byte[] data = new byte[mBufferSize];
        try {
            in = new FileInputStream(inFilename);
            out = new FileOutputStream(outFilename);
            totalAudioLen = in.getChannel().size();
            totalDataLen = totalAudioLen + 36;

            writeWaveFileHeader(out, totalAudioLen, totalDataLen,
                longSampleRate, channels, byteRate);
            while (in.read(data) != -1) {
                out.write(data);
            }
            in.close();
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    /** * 加入wav文件頭 */
    private void writeWaveFileHeader(FileOutputStream out, long totalAudioLen, long totalDataLen, long longSampleRate, int channels, long byteRate) throws IOException {
        byte[] header = new byte[44];
        // RIFF/WAVE header
        header[0] = 'R';
        header[1] = 'I';
        header[2] = 'F';
        header[3] = 'F';
        header[4] = (byte) (totalDataLen & 0xff);
        header[5] = (byte) ((totalDataLen >> 8) & 0xff);
        header[6] = (byte) ((totalDataLen >> 16) & 0xff);
        header[7] = (byte) ((totalDataLen >> 24) & 0xff);
        //WAVE
        header[8] = 'W';
        header[9] = 'A';
        header[10] = 'V';
        header[11] = 'E';
        // 'fmt ' chunk
        header[12] = 'f';
        header[13] = 'm';
        header[14] = 't';
        header[15] = ' ';
        // 4 bytes: size of 'fmt ' chunk
        header[16] = 16;
        header[17] = 0;
        header[18] = 0;
        header[19] = 0;
        // format = 1
        header[20] = 1;
        header[21] = 0;
        header[22] = (byte) channels;
        header[23] = 0;
        header[24] = (byte) (longSampleRate & 0xff);
        header[25] = (byte) ((longSampleRate >> 8) & 0xff);
        header[26] = (byte) ((longSampleRate >> 16) & 0xff);
        header[27] = (byte) ((longSampleRate >> 24) & 0xff);
        header[28] = (byte) (byteRate & 0xff);
        header[29] = (byte) ((byteRate >> 8) & 0xff);
        header[30] = (byte) ((byteRate >> 16) & 0xff);
        header[31] = (byte) ((byteRate >> 24) & 0xff);
        // block align
        header[32] = (byte) (2 * 16 / 8);
        header[33] = 0;
        // bits per sample
        header[34] = 16;
        header[35] = 0;
        //data
        header[36] = 'd';
        header[37] = 'a';
        header[38] = 't';
        header[39] = 'a';
        header[40] = (byte) (totalAudioLen & 0xff);
        header[41] = (byte) ((totalAudioLen >> 8) & 0xff);
        header[42] = (byte) ((totalAudioLen >> 16) & 0xff);
        header[43] = (byte) ((totalAudioLen >> 24) & 0xff);
        out.write(header, 0, 44);
    }
}
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總結

到這裏, 就能夠進行音頻錄製啦