本demo主要针对于声音波形播放的演示。
本demo中应用了很多知识点，在后面一一进行介绍和解读，现在先上一下本demo的运行界面。
接下来看一下简单的波形控件自定义类
class VisualizerView extends View {
private byte[] mBytes;
private float[] mPoints;
private Rect mRect = new Rect();
private Paint mForePaint = new Paint();
public VisualizerView(Context context) {
super(context);
init();
}
private void init() {
mBytes = null;
mForePaint.setStrokeWidth(1f);
mForePaint.setAntiAlias(true);
mForePaint.setColor(Color.rgb(0, 128, 255));
}
public void updateVisualizer(byte[] bytes) {
mBytes = bytes;
invalidate();
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (mBytes == null) {
return;
}
if (mPoints == null || mPoints.length < mBytes.length * 4) {
mPoints = new float[mBytes.length * 4];
}
mRect.set(0, 0, getWidth(), getHeight());
for (int i = 0; i < mBytes.length - 1; i++) {
mPoints[i * 4] = mRect.width() * i / (mBytes.length - 1);
mPoints[i * 4 + 1] = mRect.height() / 2
+ ((byte) (mBytes[i] + 128)) * (mRect.height() / 2) / 128;
mPoints[i * 4 + 2] = mRect.width() * (i + 1) / (mBytes.length - 1);
mPoints[i * 4 + 3] = mRect.height() / 2
+ ((byte) (mBytes[i + 1] + 128)) * (mRect.height() / 2) / 128;
}
canvas.drawLines(mPoints, mForePaint);
}
}
自定义控件的知识，就不在此处赘述了，有兴趣的小伙伴可以翻阅之前的自定义控件章节。
接下来看下运行时的Activity
做频谱应用到了Visualizer 类，这个类只在Android 2.3以上的API才支持
public class AudioFxDemo extends Activity {
private static final String TAG = "AudioFxDemo";
private static final float VISUALIZER_HEIGHT_DIP = 50f;
private MediaPlayer mMediaPlayer;
private Visualizer mVisualizer;
private Equalizer mEqualizer;
private LinearLayout mLinearLayout;
private VisualizerView mVisualizerView;
private TextView mStatusTextView;
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setVolumeControlStream(AudioManager.STREAM_MUSIC);
mStatusTextView = new TextView(this);
mLinearLayout = new LinearLayout(this);
mLinearLayout.setOrientation(LinearLayout.VERTICAL);
mLinearLayout.addView(mStatusTextView);
setContentView(mLinearLayout);
//创建媒体播放器Create the MediaPlayer
mMediaPlayer = MediaPlayer.create(this, R.raw.test_cbr);
/ /创建一个VisualizerView(自定义)，它将呈现简化的音频波浪形式到画布。
setupVisualizerFxAndUI();
setupEqualizerFxAndUI();
// Make sure the visualizer is enabled only when you actually want to receive data, and
// when it makes sense to receive data.
mVisualizer.setEnabled(true);
// When the stream ends, we don't need to collect any more data. We don't do this in
// setupVisualizerFxAndUI because we likely want to have more, non-Visualizer related code
// in this callback.
mMediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
public void onCompletion(MediaPlayer mediaPlayer) {
mVisualizer.setEnabled(false);
}
});
mMediaPlayer.start();
mStatusTextView.setText("Playing audio...");
}
private void setupEqualizerFxAndUI() {
/ /创建均衡器对象(一个AudioEffect子类)并将其附加到我们的媒体播放器上， 具有默认优先级(0)。
mEqualizer = new Equalizer(0, mMediaPlayer.getAudioSessionId());
mEqualizer.setEnabled(true);
TextView eqTextView = new TextView(this);
eqTextView.setText("Equalizer:");
mLinearLayout.addView(eqTextView);
short bands = mEqualizer.getNumberOfBands();
final short minEQLevel = mEqualizer.getBandLevelRange()[0];
final short maxEQLevel = mEqualizer.getBandLevelRange()[1];
for (short i = 0; i < bands; i++) {
final short band = i;
TextView freqTextView = new TextView(this);
freqTextView.setLayoutParams(new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.FILL_PARENT,
ViewGroup.LayoutParams.WRAP_CONTENT));
freqTextView.setGravity(Gravity.CENTER_HORIZONTAL);
freqTextView.setText((mEqualizer.getCenterFreq(band) / 1000) + " Hz");
mLinearLayout.addView(freqTextView);
LinearLayout row = new LinearLayout(this);
row.setOrientation(LinearLayout.HORIZONTAL);
TextView minDbTextView = new TextView(this);
minDbTextView.setLayoutParams(new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT));
minDbTextView.setText((minEQLevel / 100) + " dB");
TextView maxDbTextView = new TextView(this);
maxDbTextView.setLayoutParams(new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT));
maxDbTextView.setText((maxEQLevel / 100) + " dB");
LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.FILL_PARENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
layoutParams.weight = 1;
SeekBar bar = new SeekBar(this);
bar.setLayoutParams(layoutParams);
bar.setMax(maxEQLevel - minEQLevel);
bar.setProgress(mEqualizer.getBandLevel(band));
bar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser) {
mEqualizer.setBandLevel(band, (short) (progress + minEQLevel));
}
public void onStartTrackingTouch(SeekBar seekBar) {}
public void onStopTrackingTouch(SeekBar seekBar) {}
});
row.addView(minDbTextView);
row.addView(bar);
row.addView(maxDbTextView);
mLinearLayout.addView(row);
}
}
private void setupVisualizerFxAndUI() {
// Create a VisualizerView (defined below), which will render the simplified audio
// wave form to a Canvas.
mVisualizerView = new VisualizerView(this);
mVisualizerView.setLayoutParams(new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.FILL_PARENT,
(int)(VISUALIZER_HEIGHT_DIP * getResources().getDisplayMetrics().density)));
mLinearLayout.addView(mVisualizerView);
// 首先实例化Visualizer，参数SessionId可以通过MediaPlayer的对象获得
mVisualizer = new Visualizer(mMediaPlayer.getAudioSessionId());
//接着设置需要转换的音乐内容长度，专业的说这就是采样，该采样值一般为2的指数倍，如64,128,256,512,1024 mVisualizer.setCaptureSize(Visualizer.getCaptureSizeRange()[1]);
//为visualizer设置监听器，当Capture一段数据后，就会触发两个函数进行处理samplingRate是采样速率，即rate值，512mHz。其中两个byte[] waveform和byte[] fft数组，分别是获得波形数据和FFT的数据，该byte数组的大小即为之前设置的采样值大小128，获得数据如下图所示。其中n为采样值，index 0 表示直流分量，Rf表示FFT计算后的实部，If表示FFT计算后的虚部。 mVisualizer.setDataCaptureListener(new Visualizer.OnDataCaptureListener() { public void onWaveFormDataCapture(Visualizer visualizer, byte[] bytes, int samplingRate) { mVisualizerView.updateVisualizer(bytes); } public void onFftDataCapture(Visualizer visualizer, byte[] bytes, int samplingRate) {} }, Visualizer.getMaxCaptureRate() / 2, true, false); }//暂停播放器 @Override protected void onPause() { super.onPause(); if (isFinishing() && mMediaPlayer != null) { mVisualizer.release(); mEqualizer.release(); mMediaPlayer.release(); mMediaPlayer = null; } }}