feat(android): allow saving recorded audio as wav on startRealtimeTra…

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* feat: android startRealtimeTranscribe allow saving recorded audio as .wav

This change allows use cases such as playing back audio while highlighting the current audio segment

* style: remove uneeded changes to spacing

bad prettier format

* fix: remove forced .wav extension on written audio files

Fix to comment

* fix: update audioOutputPath comment

---------

Co-authored-by: Jhen-Jie Hong <iainst0409@gmail.com>

android/src/main/java/com/rnwhisper/WhisperContext.java

@@ -24,6 +24,8 @@
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.DataOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.PushbackInputStream;
@@ -86,6 +88,80 @@ private void rewind() {
     fullHandler = null;
   }
 
+  public byte[] shortToByte(short[] shortInts) {
+    int j = 0;
+    int length = shortInts.length;
+    byte[] byteData = new byte[length * 2];
+    for (int i = 0; i < length; i++) {
+      byteData[j++] = (byte) (shortInts[i] >>> 8);
+      byteData[j++] = (byte) (shortInts[i] >>> 0);
+    }
+    return byteData;
+  }
+
+  public byte[] concatShortBuffers(ArrayList<short[]> buffers) {
+    int totalLength = 0;
+    for (int i = 0; i < buffers.size(); i++) {
+      totalLength += buffers.get(i).length;
+    }
+    byte[] result = new byte[totalLength * 2];
+    int offset = 0;
+    for (int i = 0; i < buffers.size(); i++) {
+      byte[] bytes = shortToByte(buffers.get(i));
+      System.arraycopy(bytes, 0, result, offset, bytes.length);
+      offset += bytes.length;
+    }
+
+    return result;
+  }
+
+  public byte[] removeTrailingZeros(byte[] audioData) {
+    int i = audioData.length - 1;
+    while (i >= 0 && audioData[i] == 0) {
+      --i;
+    }
+    byte[] newData = new byte[i + 1];
+    System.arraycopy(audioData, 0, newData, 0, i + 1);
+    return newData;
+  }
+
+  private void saveWavFile(byte[] rawData, String audioOutputFile) throws IOException {
+    Log.d(NAME, "call saveWavFile");
+    rawData = removeTrailingZeros(rawData);
+    DataOutputStream output = null;
+    try {
+      output = new DataOutputStream(new FileOutputStream(audioOutputFile));
+      // WAVE header
+      // see http://ccrma.stanford.edu/courses/422/projects/WaveFormat/
+      output.writeBytes("RIFF"); // chunk id
+      output.writeInt(Integer.reverseBytes(36 + rawData.length)); // chunk size
+      output.writeBytes("WAVE"); // format
+      output.writeBytes("fmt "); // subchunk 1 id
+      output.writeInt(Integer.reverseBytes(16)); // subchunk 1 size
+      output.writeShort(Short.reverseBytes((short) 1)); // audio format (1 = PCM)
+      output.writeShort(Short.reverseBytes((short) 1)); // number of channels
+      output.writeInt(Integer.reverseBytes(SAMPLE_RATE)); // sample rate
+      output.writeInt(Integer.reverseBytes(SAMPLE_RATE * 2)); // byte rate
+      output.writeShort(Short.reverseBytes((short) 2)); // block align
+      output.writeShort(Short.reverseBytes((short) 16)); // bits per sample
+      output.writeBytes("data"); // subchunk 2 id
+      output.writeInt(Integer.reverseBytes(rawData.length)); // subchunk 2 size
+      // Audio data (conversion big endian -> little endian)
+      short[] shorts = new short[rawData.length / 2];
+      ByteBuffer.wrap(rawData).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(shorts);
+      ByteBuffer bytes = ByteBuffer.allocate(shorts.length * 2);
+      for (short s : shorts) {
+        bytes.putShort(s);
+      }
+      Log.d(NAME, "writing audio file: " + audioOutputFile);
+      output.write(bytes.array());
+    } finally {
+      if (output != null) {
+        output.close();
+      }
+    }
+  }
+
   public int startRealtimeTranscribe(int jobId, ReadableMap options) {
     if (isCapturing || isTranscribing) {
       return -100;
@@ -111,6 +187,8 @@ public int startRealtimeTranscribe(int jobId, ReadableMap options) {
 
     isUseSlices = audioSliceSec < audioSec;
 
+    String audioOutputPath = options.hasKey("audioOutputPath") ? options.getString("audioOutputPath") : null;
+
     shortBufferSlices = new ArrayList<short[]>();
     shortBufferSlices.add(new short[audioSliceSec * SAMPLE_RATE]);
     sliceNSamples = new ArrayList<Integer>();
@@ -183,6 +261,8 @@ public void run() {
               Log.e(NAME, "Error transcribing realtime: " + e.getMessage());
             }
           }
+          Log.d(NAME, "Begin saving wav file to " + audioOutputPath);
+          saveWavFile(concatShortBuffers(shortBufferSlices), audioOutputPath);
           if (!isTranscribing) {
             emitTranscribeEvent("@RNWhisper_onRealtimeTranscribeEnd", Arguments.createMap());
           }

src/index.ts

@@ -58,6 +58,12 @@ export type TranscribeRealtimeOptions = TranscribeOptions & {
    * (Default: Equal to `realtimeMaxAudioSec`)
    */
   realtimeAudioSliceSec?: number
+  /**
+   * Output path for audio file. If not set, the audio file will not be saved
+   * TODO: Support iOS
+   * (Default: Undefined)
+   */
+  audioOutputPath?: string
 }
 
 export type TranscribeRealtimeEvent = {