Android多媒体编程基础

#多媒体概念
* 文字、图片、音频、视频
#计算机图片大小的计算
> 图片大小 = 图片的总像素 * 每个像素占用的大小

* 单色图：每个像素占用1/8个字节
* 16色图：每个像素占用1/2个字节
* 256色图：每个像素占用1个字节
* 24位图：每个像素占用3个字节

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#加载大图片到内存
>Android系统以ARGB表示每个像素，所以每个像素占用4个字节，很容易内存溢出

##对图片进行缩放
* 获取屏幕宽高

        Display dp = getWindowManager().getDefaultDisplay();
        int screenWidth = dp.getWidth();
        int screenHeight = dp.getHeight();
* 获取图片宽高

        Options opts = new Options();
        //请求图片属性但不申请内存
        opts.inJustDecodeBounds = true;
        BitmapFactory.decodeFile("sdcard/dog.jpg", opts);
        int imageWidth = opts.outWidth;
        int imageHeight = opts.outHeight;
* 图片的宽高除以屏幕宽高，算出宽和高的缩放比例，取较大值作为图片的缩放比例
 
        int scale = 1;
        int scaleX = imageWidth / screenWidth;
        int scaleY = imageHeight / screenHeight;
        if(scaleX >= scaleY && scaleX > 1){
            scale = scaleX;
        }
        else if(scaleY > scaleX && scaleY > 1){
            scale = scaleY;
        }
* 按缩放比例加载图片

        //设置缩放比例
        opts.inSampleSize = scale;
        //为图片申请内存
        opts.inJustDecodeBounds = false;
        Bitmap bm = BitmapFactory.decodeFile("sdcard/dog.jpg", opts);
        iv.setImageBitmap(bm);

---
#在内存中创建图片的副本
>直接加载的bitmap对象是只读的，无法修改，要修改图片只能在内存中创建出一个一模一样的bitmap副本，然后修改副本
        
        //加载原图
        Bitmap srcBm = BitmapFactory.decodeFile("sdcard/photo3.jpg");
        iv_src.setImageBitmap(srcBm);
        
        //创建与原图大小一致的空白bitmap
        Bitmap copyBm = Bitmap.createBitmap(srcBm.getWidth(), srcBm.getHeight(), srcBm.getConfig());
        //定义画笔
        Paint paint = new Paint();
        //把纸铺在画版上
        Canvas canvas = new Canvas(copyBm);
        //把srcBm的内容绘制在copyBm上
        canvas.drawBitmap(srcBm, new Matrix(), paint);
        
        iv_copy.setImageBitmap(copyBm);
##对图片进行特效处理
* 首先定义一个矩阵对象

        Matrix mt = new Matrix();
* 缩放效果

        //x轴缩放1倍，y轴缩放0.5倍
        mt.setScale(1, 0.5f);

* 旋转效果

        //以copyBm.getWidth() / 2, copyBm.getHeight() / 2点为轴点，顺时旋转30度
        mt.setRotate(30, copyBm.getWidth() / 2, copyBm.getHeight() / 2);
* 平移

        //x轴坐标+10，y轴坐标+20
        mt.setTranslate(10, 20);
* 镜面

        //把X坐标都变成负数
        mt.setScale(-1, 1);
        //图片整体向右移
        mt.postTranslate(copyBm.getWidth(), 0);
* 倒影

        //把Y坐标都变成负数
        mt.setScale(1, -1);
        //图片整体向下移
        mt.postTranslate(0, copyBm.getHeight());

---
#画画板
>记录用户触摸事件的XY坐标，绘制直线
* 给ImageView设置触摸侦听，得到用户的触摸事件，并获知用户触摸ImageView的坐标

        iv.setOnTouchListener(new OnTouchListener() {
            
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                // TODO Auto-generated method stub
                switch (event.getAction()) {
                //触摸屏幕
                case MotionEvent.ACTION_DOWN:
                    //得到触摸屏幕时手指的坐标
                    startX = (int) event.getX();
                    startY = (int) event.getY();
                    break;
                //在屏幕上滑动
                case MotionEvent.ACTION_MOVE:
                    //用户滑动手指，坐标不断的改变，获取最新坐标
                    int newX = (int) event.getX();
                    int newY = (int) event.getY();
                    //用上次onTouch方法得到的坐标和本次得到的坐标绘制直线
                    canvas.drawLine(startX, startY, newX, newY, paint);
                    iv.setImageBitmap(copyBm);
                    startX = newX;
                    startY = newY;
                    break;

                }
                return true;
            }
        });
* 刷子效果，加粗画笔

        paint.setStrokeWidth(8);
* 调色板，改变画笔颜色

        paint.setColor(Color.GREEN);
* 保存图片至SD卡

        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(new File("sdcard/dazuo.png"));
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        //保存图片
        copyBm.compress(CompressFormat.PNG, 100, fos);
* 系统每次收到SD卡就绪广播时，都会去遍历sd卡的所有文件和文件夹，把遍历到的所有多媒体文件都在MediaStore数据库保存一个索引，这个索引包含多媒体文件的文件名、路径、大小
* 图库每次打开时，并不会去遍历sd卡获取图片，而是通过内容提供者从MediaStore数据库中获取图片的信息，然后读取该图片
* 系统开机或者点击加载sd卡按钮时，系统会发送sd卡就绪广播，我们也可以手动发送就绪广播

        Intent intent = new Intent();
        intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
        intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));
        sendBroadcast(intent);

---
#撕衣服
* 原理：把穿内衣和穿外衣的照片重叠显示，内衣照在下面，用户滑动屏幕时，触摸的是外衣照，把手指经过的像素都置为透明，内衣照就显示出来了

         iv.setOnTouchListener(new OnTouchListener() {
            
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                case MotionEvent.ACTION_MOVE:
                    int newX = (int) event.getX();
                    int newY = (int) event.getY();
                    //把指定的像素变成透明
                    copyBm.setPixel(newX, newY, Color.TRANSPARENT);
                    iv.setImageBitmap(copyBm);
                    break;

                }
                return true;
            }
        });
* 每次只设置一个像素点太慢，以触摸的像素为圆心，半径为5画圆，圆内的像素全部置为透明

        for (int i = -5; i < 6; i++) {
            for (int j = -5; j < 6; j++) {
                if(Math.sqrt(i * i + j * j) <= 5)
                    copyBm.setPixel(newX + i, newY + j, Color.TRANSPARENT);
            }
        }

---
#音乐播放器
##播放服务
* 播放音频的代码应该运行在服务中，定义一个播放服务MusicService
* 服务里定义play、stop、pause、continuePlay等方法

            private void play() {
                // TODO Auto-generated method stub
                player.reset();
                try {
                    player.setDataSource("sdcard/bzj.mp3");
                    player.prepare();
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } 
                player.start();
                
            }
            private void pause() {
                player.pause();
            }
            private void stop() {
                player.stop();
            }
            private void continuePlay() {
                player.start();
            }
* 把这几个方法抽取成一个接口MusicInterface
* 定义一个中间人类，继承Binder，实现MusicInterface
* 先start启动MusicService，再bind

        Intent intent = new Intent(this, MusicService.class);
        startService(intent);
        bindService(intent, conn, BIND_AUTO_CREATE);
##根据播放进度设置进度条
* 获取当前的播放时间和当前音频的最长时间

        int currentPosition = player.getCurrentPosition();
        int duration = player.getDuration();
* 播放进度需要不停的获取，不停的刷新进度条，使用计时器每500毫秒获取一次播放进度
* 发消息至Handler，把播放进度放进Message对象中，在Handler中更新SeekBar的进度

        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            
            @Override
            public void run() {
                int currentPosition = player.getCurrentPosition();
                int duration = player.getDuration();
                Message msg = Message.obtain();
                //把播放进度存入Message中
                Bundle data = new Bundle();
                data.putInt("currentPosition", currentPosition);
                data.putInt("duration", duration);
                msg.setData(data);
                MainActivity.handler.sendMessage(msg);
            }
        }, 5, 500);
* 在Activity中定义Handler

        static Handler handler = new Handler(){
            public void handleMessage(android.os.Message msg) {
                //取出消息携带的数据
                Bundle data = msg.getData();
                int currentPosition = data.getInt("currentPosition");
                int duration = data.getInt("duration");
            
                //设置播放进度
                sb.setMax(duration);
                sb.setProgress(currentPosition);
            };
        };
##拖动进度条改变播放进度

         //给sb设置一个拖动侦听
         sb.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
            //停止拖动时调用
            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
                // TODO Auto-generated method stub
                int progress = seekBar.getProgress();
                mi.seekTo(progress);
            }
            //开始拖动时调用            
            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {
                // TODO Auto-generated method stub
                
            }
            //拖动的时候不断调用            
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress,
                    boolean fromUser) {
                // TODO Auto-generated method stub
                
            }
        });    

---
#视频播放器
##SurfaceView
* 对画面的实时更新要求较高
* 双缓冲技术：内存中有两个画布，A画布显示至屏幕，B画布在内存中绘制下一帧画面，绘制完毕后B显示至屏幕，A在内存中继续绘制下一帧画面
* 播放视频也是用MediaPlayer，不过跟音频不同，要设置显示在哪个SurfaceView

        SurfaceView sv = (SurfaceView) findViewById(R.id.sv);
        SurfaceHolder sh = sv.getHolder();
                        
        MediaPlayer player = new MediaPlayer();
        player.reset();
        try {
            player.setDataSource("sdcard/2.3gp");
            player.setDisplay(sh);
            player.prepare();
        } catch (Exception e) {
            e.printStackTrace();
        }
        player.start();
* SurfaceView是重量级组件，可见时才会创建
* 给SurfaceHolder设置CallBack，类似于侦听，可以知道SurfaceView的状态

        sh.addCallback(new Callback() {
            //SurfaceView销毁时调用
            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {
                // TODO Auto-generated method stub
                
            }
            //SurfaceView创建时调用
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                // TODO Auto-generated method stub
                
            }
            
            @Override
            public void surfaceChanged(SurfaceHolder holder, int format, int width,
                    int height) {
                // TODO Auto-generated method stub
                
            }
        });
* SurfaceView一旦不可见，就会被销毁，一旦可见，就会被创建，销毁时停止播放，再次创建时再开始播放


---
#摄像头
* 启动系统提供的拍照程序

        //隐式启动系统提供的拍照Activity
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        //设置照片的保存路径
        File file = new File(Environment.getExternalStorageDirectory(), "haha.jpg"); 
        intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(file)); 
        startActivityForResult(intent, 0);
* 启动系统提供的摄像程序

        Intent intent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);

        File file = new File(Environment.getExternalStorageDirectory(), "haha.3gp"); 
        intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(file)); 
        //设置保存视频文件的质量
        intent.putExtra(MediaStore.EXTRA_VIDEO_QUALITY, 1);
        startActivityForResult(intent, 0);