content: /*
   * Copyright (C) 2015 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.example.android.common.midi.synth;
  
  import android.media.AudioFormat;
  import android.media.AudioManager;
  import android.media.AudioTrack;
  import android.util.Log;
  
  /**
   * Simple base class for implementing audio output for examples.
   * This can be sub-classed for experimentation or to redirect audio output.
   */
  public class SimpleAudioOutput {
  
      private static final String TAG = "AudioOutputTrack";
      public static final int SAMPLES_PER_FRAME = 2;
      public static final int BYTES_PER_SAMPLE = 4; // float
      public static final int BYTES_PER_FRAME = SAMPLES_PER_FRAME * BYTES_PER_SAMPLE;
      private AudioTrack mAudioTrack;
      private int mFrameRate;
  
      /**
       *
       */
      public SimpleAudioOutput() {
          super();
      }
  
      /**
       * Create an audio track then call play().
       *
       * @param frameRate
       */
      public void start(int frameRate) {
          stop();
          mFrameRate = frameRate;
          mAudioTrack = createAudioTrack(frameRate);
          // AudioTrack will wait until it has enough data before starting.
          mAudioTrack.play();
      }
  
      public AudioTrack createAudioTrack(int frameRate) {
          int minBufferSizeBytes = AudioTrack.getMinBufferSize(frameRate,
                  AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_FLOAT);
          Log.i(TAG, "AudioTrack.minBufferSize = " + minBufferSizeBytes
                  + " bytes = " + (minBufferSizeBytes / BYTES_PER_FRAME)
                  + " frames");
          int bufferSize = 8 * minBufferSizeBytes / 8;
          int outputBufferSizeFrames = bufferSize / BYTES_PER_FRAME;
          Log.i(TAG, "actual bufferSize = " + bufferSize + " bytes = "
                  + outputBufferSizeFrames + " frames");
  
          AudioTrack player = new AudioTrack(AudioManager.STREAM_MUSIC,
                  mFrameRate, AudioFormat.CHANNEL_OUT_STEREO,
                  AudioFormat.ENCODING_PCM_FLOAT, bufferSize,
                  AudioTrack.MODE_STREAM);
          Log.i(TAG, "created AudioTrack");
          return player;
      }
  
      public int write(float[] buffer, int offset, int length) {
          return mAudioTrack.write(buffer, offset, length,
                  AudioTrack.WRITE_BLOCKING);
      }
  
      public void stop() {
          if (mAudioTrack != null) {
              mAudioTrack.stop();
              mAudioTrack = null;
          }
      }
  
      public int getFrameRate() {
          return mFrameRate;
      }
  
      public AudioTrack getAudioTrack() {
          return mAudioTrack;
      }
  }
  