Android音频开发（7）：音乐可视化-FFT频谱图

项目地址：https://github.com/zhaolewei/MusicVisualizer
视频演示地址：https://www.bilibili.com/video/av30388154/

一、演示

image

二、实现

• 实现流程：

1. 使用MediaPlayer播放传入的音乐，并拿到mediaPlayerId
2. 使用Visualizer类拿到拿到MediaPlayer播放中的音频数据（wave/fft）
3. 将数据用自定义控件展现出来

三、准备工作

• 使用Visualizer需要录音的动态权限， 如果播放sd卡音频需要STORAGE权限

      private static final String[] PERMISSIONS = new String[]{
            Manifest.permission.RECORD_AUDIO,
            Manifest.permission.MODIFY_AUDIO_SETTINGS
      };
      
      ActivityCompat.requestPermissions(MainActivity.this, PERMISSIONS, 1);
      
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

四、开始播放

private MediaPlayer.OnPreparedListener preparedListener = new 
    /**
     * 播放音频
     *
     * @param raw 资源文件id
     */
    private  void doPlay(final int raw) {
        try {
            mediaPlayer = MediaPlayer.create(MyApp.getInstance(), raw);
            if (mediaPlayer == null) {
                Logger.e(TAG, "mediaPlayer is null");
                return;
            }

            mediaPlayer.setOnErrorListener(errorListener);
            mediaPlayer.setOnPreparedListener(preparedListener);
        } catch (Exception e) {
            Logger.e(e, TAG, e.getMessage());
        }
    }
    
    /**
    * 获取MediaPlayerId
    * 可视化类Visualizer需要此参数
    * @return  MediaPlayerId
    */
    public int getMediaPlayerId() {
        return mediaPlayer.getAudioSessionId();
    }

五、使用可视化类Visualizer获取当前音频数据

Visualizer 有两个比较重要的参数

1. 设置可视化数据的数据大小 范围[Visualizer.getCaptureSizeRange()[0]~Visualizer.getCaptureSizeRange()[1]]
2. 社会可视化数据的采集频率 范围[0~Visualizer.getMaxCaptureRate()]

• OnDataCaptureListener 有2个回调，一个用于显示FFT数据，展示不同频率的振幅，另一个用于显示声音的波形图

private Visualizer.OnDataCaptureListener dataCaptureListener = new Visualizer.OnDataCaptureListener() {
        @Override
        public void onWaveFormDataCapture(Visualizer visualizer, final byte[] waveform, int samplingRate) {
            audioView.post(new Runnable() {
                @Override
                public void run() {
                    audioView.setWaveData(waveform);
                }
            });
        }

        @Override
        public void onFftDataCapture(Visualizer visualizer, final byte[] fft, int samplingRate) {
            audioView2.post(new Runnable() {
                @Override
                public void run() {
                    audioView2.setWaveData(fft);
                }
            });
        }
    };
    
private void initVisualizer() {
    try {
        int mediaPlayerId = mediaPlayer.getMediaPlayerId();
        if (visualizer != null) {
            visualizer.release();
        }
        visualizer = new Visualizer(mediaPlayerId);
        
        /**
         *可视化数据的大小： getCaptureSizeRange()[0]为最小值，getCaptureSizeRange()[1]为最大值
         */
        int captureSize = Visualizer.getCaptureSizeRange()[1];
        int captureRate = Visualizer.getMaxCaptureRate() * 3 / 4;
        
        visualizer.setCaptureSize(captureSize);
        visualizer.setDataCaptureListener(dataCaptureListener, captureRate, true, true);
        visualizer.setScalingMode(Visualizer.SCALING_MODE_NORMALIZED);
        visualizer.setEnabled(true);
    } catch (Exception e) {
        Logger.e(TAG, "请检查录音权限");
    }
}    

波形数据和傅里叶数据的关系请看面这张图：

image

六、编写自定义控件，展示数据

1. 处理数据： visualizer 回调中的数据中是存在负数的，需要转换一下，用于显示

• 当byte 为 -128时Math.abs(fft[i]) 计算出来的值会越界，需要手动处理一下

byte 的范围： -128~127

    /**
     * 预处理数据
     *
     * @return
     */
    private static byte[] readyData(byte[] fft) {
        byte[] newData = new byte[LUMP_COUNT];
        byte abs;
        for (int i = 0; i < LUMP_COUNT; i++) {
            abs = (byte) Math.abs(fft[i]);
            //描述：Math.abs -128时越界
            newData[i] = abs < 0 ? 127 : abs;
        }
        return newData;
    }

2. 紧接着就是根据数据去绘制图形

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        wavePath.reset();

        for (int i = 0; i < LUMP_COUNT; i++) {
            if (waveData == null) {
                canvas.drawRect((LUMP_WIDTH + LUMP_SPACE) * i,
                        LUMP_MAX_HEIGHT - LUMP_MIN_HEIGHT,
                        (LUMP_WIDTH + LUMP_SPACE) * i + LUMP_WIDTH,
                        LUMP_MAX_HEIGHT,
                        lumpPaint);
                continue;
            }

            switch (upShowStyle) {
                case STYLE_HOLLOW_LUMP:
                    drawLump(canvas, i, false);
                    break;
                case STYLE_WAVE:
                    drawWave(canvas, i, false);
                    break;
                default:
                    break;
            }

            switch (downShowStyle) {
                case STYLE_HOLLOW_LUMP:
                    drawLump(canvas, i, true);
                    break;
                case STYLE_WAVE:
                    drawWave(canvas, i, true);
                    break;
                default:
                    break;
            }
        }
    }
    
    /**
     * 绘制矩形条
     */
    private void drawLump(Canvas canvas, int i, boolean reversal) {
        int minus = reversal ? -1 : 1;

        if (waveData[i] < 0) {
            Logger.w("waveData", "waveData[i] < 0 data: %s", waveData[i]);
        }
        float top = (LUMP_MAX_HEIGHT - (LUMP_MIN_HEIGHT + waveData[i] * SCALE) * minus);

        canvas.drawRect(LUMP_SIZE * i,
                top,
                LUMP_SIZE * i + LUMP_WIDTH,
                LUMP_MAX_HEIGHT,
                lumpPaint);
    }

    /**
     * 绘制曲线
     * 这里使用贝塞尔曲线来绘制
     */
    private void drawWave(Canvas canvas, int i, boolean reversal) {
        if (pointList == null || pointList.size() < 2) {
            return;
        }
        float ratio = SCALE * (reversal ? -1 : 1);
        if (i < pointList.size() - 2) {
            Point point = pointList.get(i);
            Point nextPoint = pointList.get(i + 1);
            int midX = (point.x + nextPoint.x) >> 1;
            if (i == 0) {
                wavePath.moveTo(point.x, LUMP_MAX_HEIGHT - point.y * ratio);
            }
            wavePath.cubicTo(midX, LUMP_MAX_HEIGHT - point.y * ratio,
                    midX, LUMP_MAX_HEIGHT - nextPoint.y * ratio,
                    nextPoint.x, LUMP_MAX_HEIGHT - nextPoint.y * ratio);

            canvas.drawPath(wavePath, lumpPaint);
        }
    }