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@DevWiki 2018-12-06T15:40:54.000000Z 字数 5530 阅读 4722

Android中Pcm文件转Amr文件

Android

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最经在做一个聊天的模块,聊天的模块很简单:

录音-上传-接收-播放

录音

录音部分可以采用MediaRecord和AudioRecord两个类进行录音.但是各有优缺点.

MediaRecord已经封装了很多方法,方便使用.
AudioRecord能获取录音的原生数据,以便对录音二次加工.

在录音过程我采用的是AudioRecord.但是AudioRecord录音数据是PCM格式,数据占用存储空间很大.必须压缩后才能传输.项目中的压缩是项目其他成员写的一个so库进行压缩的,有点不太方便.在网上翻阅了下,其实Android系统内部已经携带有压缩的库文件了.

压缩库

Android自带的有一个Pcm转amr的库:media_jni.so.
但是由于是Android系统内部的库,无法直接使用.根据网上的说明,最终终于弄明白如何使用了.

AmrInputStream

在要使用压缩库的项目中新建包:

  1. com.android.media

在此包中新建AmrInputStream类,代码如下:

  1. public final class AmrInputStream extends InputStream {
  3.     static {
  4.         System.loadLibrary("media_jni");
  5.     }
  7.     private final static String TAG = "AmrInputStream";
  9.     // frame is 20 msec at 8.000 khz
  10.     private final static int SAMPLES_PER_FRAME = 8000 * 20 / 1000;
  12.     // pcm input stream
  13.     private InputStream mInputStream;
  15.     // native handle
  16.     private int mGae;
  18.     // result amr stream
  19.     private byte[] mBuf = new byte[SAMPLES_PER_FRAME * 2];
  20.     private int mBufIn = 0;
  21.     private int mBufOut = 0;
  23.     // helper for bytewise read()
  24.     private byte[] mOneByte = new byte[1];
  26.     /**
  27.      * Create a new AmrInputStream, which converts 16 bit PCM to AMR
  28.      * @param inputStream InputStream containing 16 bit PCM.
  29.      */
  30.     public AmrInputStream(InputStream inputStream) {
  31.         mInputStream = inputStream;
  32.         mGae = GsmAmrEncoderNew();
  33.         GsmAmrEncoderInitialize(mGae);
  34.     }
  36.     @Override
  37.     public int read() throws IOException {
  38.         int rtn = read(mOneByte, 0, 1);
  39.         return rtn == 1 ? (0xff & mOneByte[0]) : -1;
  40.     }
  42.     @Override
  43.     public int read(byte[] b) throws IOException {
  44.         return read(b, 0, b.length);
  45.     }
  47.     @Override
  48.     public int read(byte[] b, int offset, int length) throws IOException {
  49.         if (mGae == 0) throw new IllegalStateException("not open");
  51.         // local buffer of amr encoded audio empty
  52.         if (mBufOut >= mBufIn) {
  53.             // reset the buffer
  54.             mBufOut = 0;
  55.             mBufIn = 0;
  57.             // fetch a 20 msec frame of pcm
  58.             for (int i = 0; i < SAMPLES_PER_FRAME * 2; ) {
  59.                 int n = mInputStream.read(mBuf, i, SAMPLES_PER_FRAME * 2 - i);
  60.                 if (n == -1) return -1;
  61.                 i += n;
  62.             }
  64.             // encode it
  65.             mBufIn = GsmAmrEncoderEncode(mGae, mBuf, 0, mBuf, 0);
  66.         }
  68.         // return encoded audio to user
  69.         if (length > mBufIn - mBufOut) length = mBufIn - mBufOut;
  70.         System.arraycopy(mBuf, mBufOut, b, offset, length);
  71.         mBufOut += length;
  73.         return length;
  74.     }
  76.     @Override
  77.     public void close() throws IOException {
  78.         try {
  79.             if (mInputStream != null) mInputStream.close();
  80.         } finally {
  81.             mInputStream = null;
  82.             try {
  83.                 if (mGae != 0) GsmAmrEncoderCleanup(mGae);
  84.             } finally {
  85.                 try {
  86.                     if (mGae != 0) GsmAmrEncoderDelete(mGae);
  87.                 } finally {
  88.                     mGae = 0;
  89.                 }
  90.             }
  91.         }
  92.    }
  94.     @Override
  95.     protected void finalize() throws Throwable {
  96.         if (mGae != 0) {
  97.             close();
  98.             throw new IllegalStateException("someone forgot to close AmrInputStream");
  99.         }
  100.     }
  102.     //
  103.     // AudioRecord JNI interface
  104.     //
  105.     private static native int GsmAmrEncoderNew();
  106.     private static native void GsmAmrEncoderInitialize(int gae);
  107.     private static native int GsmAmrEncoderEncode(int gae,
  108.            byte[] pcm, int pcmOffset, byte[] amr, int amrOffset) throws IOException;
  109.     private static native void GsmAmrEncoderCleanup(int gae);
  110.     private static native void GsmAmrEncoderDelete(int gae);
  111. }

AmrEmcoder

只有AmrInputStream类是不够,还需要一个转码的类AmrEncoder,代码如下:

  1. public class AmrEncoder {
  3.     public static void pcm2Amr(String pcmPath , String amrPath) {
  4.         FileInputStream fis;
  5.         try {
  6.             fis = new FileInputStream(pcmPath);
  7.             pcm2Amr(fis, amrPath);
  8.             fis.close();
  9.         } catch (FileNotFoundException e1) {
  10.             e1.printStackTrace();
  11.         } catch (IOException e) {
  12.             e.printStackTrace();
  13.         }
  14.     }
  16.     public static void pcm2Amr(InputStream pcmStream, String amrPath) {
  17.         try {
  18.             AmrInputStream ais = new AmrInputStream(pcmStream);
  19.             OutputStream out = new FileOutputStream(amrPath);
  20.             byte[] buf = new byte[4096];
  21.             int len = -1;
  22.             /*
  23.              * 下面的AMR的文件头,缺少这几个字节是不行的
  24.              */
  25.             out.write(0x23);
  26.             out.write(0x21);
  27.             out.write(0x41);
  28.             out.write(0x4D);
  29.             out.write(0x52);
  30.             out.write(0x0A);   
  31.             while((len = ais.read(buf)) >0){
  32.                 out.write(buf,0,len);
  33.             }
  34.             out.close();
  35.             ais.close();
  36.         } catch (FileNotFoundException e) {
  37.             e.printStackTrace();
  38.         } catch (IOException e) {
  39.             e.printStackTrace();
  40.         }       
  41.     }
  42. }

这里有两个方法:
1. pcm2Amr(String pcmPath , String amrPath): 将pcm文件转为amr文件
2. pcm2Amr(InputStream pcmStream, String amrPath): 将pcm数据流转为amr文件

测试

测试的界面

测试的界面很简单,就一个按钮一个文本显示,布局界面就不再给出,下面是MainActivity代码:

  1. public class MainActivity extends Activity implements OnClickListener{
  3.     @Override
  4.     protected void onCreate(Bundle savedInstanceState) {
  5.         super.onCreate(savedInstanceState);
  6.         setContentView(R.layout.activity_main);
  8.         initView();
  9.     }
  11.     private TextView hintView;
  12.     private Button startButton;
  13.     private void initView() {
  14.         startButton = (Button) findViewById(R.id.btn_start);
  15.         startButton.setOnClickListener(this);
  16.         hintView = (TextView) findViewById(R.id.hint);
  17.     }
  19.     @Override
  20.     public void onClick(View v) {
  21.         if (v.getId() == R.id.btn_start) {
  22.             transferButtonClicked();
  23.         }
  24.     }
  26.     private void transferButtonClicked(){
  27.         showWaitDialog();
  28.         startTransfer();
  29.     }
  31.     private ProgressDialog waitDialog;
  32.     private void showWaitDialog(){
  33.         waitDialog = new ProgressDialog(this);
  34.         waitDialog.setTitle(getResources().getString(R.string.transfer_wait_title));
  35.         waitDialog.setMessage(getResources().getString(R.string.transfer_wait_message));
  36.         waitDialog.show();
  37.     }
  39.     private void startTransfer() {
  40.         new TransferThread(this, new TransferCallback() {
  42.             @Override
  43.             public void onSuccess() {
  44.                 transferSuccess();
  45.             }
  47.             @Override
  48.             public void onFailed() {
  49.             }
  50.         }).start();
  51.     }
  53.     private void transferSuccess() {
  54.         runOnUiThread(new Runnable() {
  56.             @Override
  57.             public void run() {
  58.                 waitDialog.dismiss();
  59.                 hintView.setText(getResources().getString(R.string.transfer_result));
  60.                 ToastUtil.showShort(MainActivity.this, R.string.success_hint);
  61.             }
  62.         });
  63.     }
  64. }

转换线程

由于文件转换是耗时操作,所以需要一个转换线程来实现文件转换.

  1. public class TransferThread extends Thread{
  3.     private TransferCallback callback;
  4.     private Context context;
  5.     public TransferThread(Context context, TransferCallback callback){
  6.         this.callback = callback;
  7.         this.context = context;
  8.     }
  10.     @Override
  11.     public void run() {
  12.         transfer();
  13.     }
  15.     private void transfer(){
  16.         String rootPath = Environment.getExternalStorageDirectory().getPath();
  17.         String amrPath = rootPath + "/test.amr";
  18.         try {
  19.             InputStream pcmStream = context.getAssets().open("test.pcm");
  20.             AmrEncoder.pcm2Amr(pcmStream, amrPath);
  21.             callback.onSuccess();
  22.         } catch (IOException e) {
  23.             callback.onFailed();
  24.             e.printStackTrace();
  25.         }
  26.     }
  29.     public static interface TransferCallback{
  30.         void onSuccess();
  32.         void onFailed();
  33.     }
  34. }

测试结果

经过测试,160KB的test.pcm压缩后的amr文件大小为15KB,且可以正常播放.

本文的项目文件在此:Pcm2Amr

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