android-audio-techniques.pdf

Tuesday, May 25, 2010 Advanced Android Audio Techniques Dave Sparks 20-May-2010 Tuesday, May 25, 2010 http://bit.ly/aDtLRp View live notes and ask questions about this session on Google Wave: Tuesday, May 25, 2010 Agenda ? Native audio signal processing ? Tips on power and resource usage ? What’s new in Froyo? ? Roadmap ? QA 4 Tuesday, May 25, 2010 Native Audio Signal Processing Tuesday, May 25, 2010 AudioTrack Overview ? Raw PCM audio API ? Streaming or static buffers ? Can set callbacks to refill buffer ? Retrieve play position ? Useful for games or streaming audio 6 Tuesday, May 25, 2010 AudioTrack Sample Code Tuesday, May 25, 2010 package com.example.audiotracksample; public class AudioTrackSample implements Runnable { static private final int mBufferSize = 8000; private AudioTrack mTrack; private short mBuffer[]; private short mSample; class AudioTrackSample { mBuffer = new short[mBufferSize]; mTrack = new AudioTrack(STREAM_MUSIC, 44100, CHANNEL_OUT_MONO, ENCODING_PCM_16BIT, mBufferSize * 2, MODE_STREAM); mSample = 0; } public void run() { mTrack.play(); while(1) { // fill the buffer generateTone(mBuffer, mBufferSize); mTrack.write(mBuffer, 0, mBufferSize); } } ... Tuesday, May 25, 2010 // continuation of class AudioTrackSample ... public void generateTone(short [] data, int size) { for (int i = 0; i size; i++) { pData[i] = mSample; mSample += 600; // ~400 Hz sawtooth } } } Tuesday, May 25, 2010 Using Native Code ? Requires the Android NDK ? Build a Java application ? Create a native library ? Add “native” methods to Java class ? Load the native library ? Call native methods from Java 10 Tuesday, May 25, 2010 AudioTrack Native Code Tuesday, May 25, 2010 package com.example.jnisample; public class JNISample implements Runnable { static private final int mBufferSize = 8000; private AudioTrack mTrack; private short mBuffer[] = new short[mBufferSize]; private int mSample; class JNISample { mBuffer = new short[bufferSize]; mTrack = n