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      1 /*
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.example.android.common.midi.synth;
     18 
     19 import android.media.AudioFormat;
     20 import android.media.AudioManager;
     21 import android.media.AudioTrack;
     22 import android.util.Log;
     23 
     24 /**
     25  * Simple base class for implementing audio output for examples.
     26  * This can be sub-classed for experimentation or to redirect audio output.
     27  */
     28 public class SimpleAudioOutput {
     29 
     30     private static final String TAG = "AudioOutputTrack";
     31     public static final int SAMPLES_PER_FRAME = 2;
     32     public static final int BYTES_PER_SAMPLE = 4; // float
     33     public static final int BYTES_PER_FRAME = SAMPLES_PER_FRAME * BYTES_PER_SAMPLE;
     34     private AudioTrack mAudioTrack;
     35     private int mFrameRate;
     36 
     37     /**
     38      *
     39      */
     40     public SimpleAudioOutput() {
     41         super();
     42     }
     43 
     44     /**
     45      * Create an audio track then call play().
     46      *
     47      * @param frameRate
     48      */
     49     public void start(int frameRate) {
     50         stop();
     51         mFrameRate = frameRate;
     52         mAudioTrack = createAudioTrack(frameRate);
     53         // AudioTrack will wait until it has enough data before starting.
     54         mAudioTrack.play();
     55     }
     56 
     57     public AudioTrack createAudioTrack(int frameRate) {
     58         int minBufferSizeBytes = AudioTrack.getMinBufferSize(frameRate,
     59                 AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_FLOAT);
     60         Log.i(TAG, "AudioTrack.minBufferSize = " + minBufferSizeBytes
     61                 + " bytes = " + (minBufferSizeBytes / BYTES_PER_FRAME)
     62                 + " frames");
     63         int bufferSize = 8 * minBufferSizeBytes / 8;
     64         int outputBufferSizeFrames = bufferSize / BYTES_PER_FRAME;
     65         Log.i(TAG, "actual bufferSize = " + bufferSize + " bytes = "
     66                 + outputBufferSizeFrames + " frames");
     67 
     68         AudioTrack player = new AudioTrack(AudioManager.STREAM_MUSIC,
     69                 mFrameRate, AudioFormat.CHANNEL_OUT_STEREO,
     70                 AudioFormat.ENCODING_PCM_FLOAT, bufferSize,
     71                 AudioTrack.MODE_STREAM);
     72         Log.i(TAG, "created AudioTrack");
     73         return player;
     74     }
     75 
     76     public int write(float[] buffer, int offset, int length) {
     77         return mAudioTrack.write(buffer, offset, length,
     78                 AudioTrack.WRITE_BLOCKING);
     79     }
     80 
     81     public void stop() {
     82         if (mAudioTrack != null) {
     83             mAudioTrack.stop();
     84             mAudioTrack = null;
     85         }
     86     }
     87 
     88     public int getFrameRate() {
     89         return mFrameRate;
     90     }
     91 
     92     public AudioTrack getAudioTrack() {
     93         return mAudioTrack;
     94     }
     95 }
     96