Android開發視訊播放器，一般都是使用MediaPlayer+SurfaceView來實現，VideoView也是使用了MediaPlayer+SurfaceView方式（不信看原始碼）。所以，我打算使用MediaPlayer+SurfaceView封裝自己的視訊播放庫。

可以看出SurfaceView佔滿整個螢幕，和match_parent的效果是一樣的，而且視訊被拉伸，嚴重變形！！這顯然不是我想要的。

之前看過VideoView的原始碼，裡面有這種變形的解決辦法。所以，開發視訊播放器，第一步，就是自定義一個適配視訊的SurfaceView。

程式碼如下：

public
 
 class VideoSurfaceView extends SurfaceView {

    // 視訊寬度
    private int videoWidth;
    // 視訊高度
    private int videoHeight;

    public VideoSurfaceView(Context context) {
        this(context, null);
    }

    public VideoSurfaceView(Context context, AttributeSet attrs) {
        this(context, attrs, 0
 
);
    }

    public VideoSurfaceView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        videoWidth = 0;
        videoHeight = 0;
        setFocusable(true);
        setFocusableInTouchMode(true);
        requestFocus();
    }

    /**
     * 根據視訊的寬高設定SurfaceView的寬高
     * @param
 
 widthMeasureSpec
     * @param heightMeasureSpec
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int width = getDefaultSize(videoWidth, widthMeasureSpec);
        int height = getDefaultSize(videoHeight, heightMeasureSpec);
        if (videoWidth > 0 && videoHeight > 0) {
            // 獲取測量模式和測量大小
            int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
            int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);
            int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
            int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);
            // 分情況設定大小
            if (widthSpecMode == MeasureSpec.EXACTLY && heightSpecMode == MeasureSpec.EXACTLY) {
                // layout_width = 確定值或match_parent
                // layout_height = 確定值或match_parent
                // the size is fixed
                width = widthSpecSize;
                height = heightSpecSize;
                // 做適配，不讓視訊拉伸，保持原來寬高的比例
                // for compatibility, we adjust size based on aspect ratio
                if ( videoWidth * height  < width * videoHeight) {
                    //Log.i("@@@", "image too wide, correcting");
                    width = height * videoWidth / videoHeight;
                } else if ( videoWidth * height  > width * videoHeight) {
                    //Log.i("@@@", "image too tall, correcting");
                    height = width * videoHeight / videoWidth;
                }
            } else if (widthSpecMode == MeasureSpec.EXACTLY) {
                // layout_width = 確定值或match_parent
                // layout_height = wrap_content
                // only the width is fixed, adjust the height to match aspect ratio if possible
                width = widthSpecSize;
                // 計算高多少，保持原來寬高的比例
                height = width * videoHeight / videoWidth;
                if (heightSpecMode == MeasureSpec.AT_MOST && height > heightSpecSize) {
                    // couldn't match aspect ratio within the constraints
                    height = heightSpecSize;
                }
            } else if (heightSpecMode == MeasureSpec.EXACTLY) {
                // layout_width = wrap_content
                // layout_height = 確定值或match_parent
                // only the height is fixed, adjust the width to match aspect ratio if possible
                height = heightSpecSize;
                // 計算寬多少，保持原來寬高的比例
                width = height * videoWidth / videoHeight;
                if (widthSpecMode == MeasureSpec.AT_MOST && width > widthSpecSize) {
                    // couldn't match aspect ratio within the constraints
                    width = widthSpecSize;
                }
            } else {
                // layout_width = wrap_content
                // layout_height = wrap_content
                // neither the width nor the height are fixed, try to use actual video size
                width = videoWidth;
                height = videoHeight;
                if (heightSpecMode == MeasureSpec.AT_MOST && height > heightSpecSize) {
                    // too tall, decrease both width and height
                    height = heightSpecSize;
                    width = height * videoWidth / videoHeight;
                }
                if (widthSpecMode == MeasureSpec.AT_MOST && width > widthSpecSize) {
                    // too wide, decrease both width and height
                    width = widthSpecSize;
                    height = width * videoHeight / videoWidth;
                }
            }
        } else {
            // no size yet, just adopt the given spec sizes
        }
        // 設定SurfaceView的寬高
        setMeasuredDimension(width, height);
    }

    /**
     * 調整大小
     * @param videoWidth
     * @param videoHeight
     */
    public void adjustSize(int videoWidth, int videoHeight) {
        if (videoWidth == 0 || videoHeight == 0) return;
        // 賦值自己的寬高
        this.videoWidth = videoWidth;
        this.videoHeight = videoHeight;
        // 設定Holder固定的大小
        getHolder().setFixedSize(videoWidth, videoHeight);
        // 重新設定自己的大小
        requestLayout();
    }

}

程式碼註釋比較清晰，相信大家看得明白！！

然後需要有個時機去呼叫自定義VideoSurfaceView的adjustSize方法來調整大小，還是參照VideoView原始碼，時機是MediaPlayer監聽到OnVideoSizeChangedListener事件：

public class MainActivity extends AppCompatActivity implements SurfaceHolder.Callback, SeekBar.OnSeekBarChangeListener,
        View.OnClickListener, MediaPlayer.OnPreparedListener, MediaPlayer.OnCompletionListener, MediaPlayer.OnErrorListener,
        MediaPlayer.OnSeekCompleteListener, MediaPlayer.OnVideoSizeChangedListener {

    // 自定義的SurfaceView
    private VideoSurfaceView surfaceView;

    /**
     * 視訊大小改變的時候呼叫
     * @param player
     * @param width
     * @param height
     */
    @Override
    public void onVideoSizeChanged(MediaPlayer player, int width, int height) {
        // 調整SurfaceView的寬高
        surfaceView.adjustSize(player.getVideoWidth(), player.getVideoHeight());
    }

    ...

    // 初始化MediaPlayer
    player = new MediaPlayer();
    // 設定視訊大小改變監聽
    player.setOnVideoSizeChangedListener(this);

}

效果圖：

如圖，VideoSurfaceView做到了適配視訊的大小。

但是還有個小問題，如果我們一開始把VideoSurfaceView設定高度為wrap_content，當MediaPlayer沒有準備好，視訊還沒有被解析成功時，VideoSurfaceView的高度還是黑黑的全屏，所以我們一開始可以把VideoSurfaceView設為一個固定值。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <com.johan.video.VideoSurfaceView
        android:id="@+id/surface_view"
        android:layout_width="match_parent"
        android:layout_height="250dp"
        />

    ...

</LinearLayout>

而且注意一點，這個值應該比視訊的高度高一點，為什麼呢？我們分析一下VideoSurfaceView的onMeasure方法：

if (widthSpecMode == MeasureSpec.EXACTLY && heightSpecMode == MeasureSpec.EXACTLY) {
    // layout_width = 確定值或match_parent
    // layout_height = 確定值或match_parent
    // the size is fixed
    width = widthSpecSize;
    height = heightSpecSize;
    // 做適配，不讓視訊拉伸，保持原來寬高的比例
    // for compatibility, we adjust size based on aspect ratio
    if ( videoWidth * height  < width * videoHeight) {
        //Log.i("@@@", "image too wide, correcting");
        width = height * videoWidth / videoHeight;
    } else if ( videoWidth * height  > width * videoHeight) {
        //Log.i("@@@", "image too tall, correcting");
        height = width * videoHeight / videoWidth;
    }
} 

如果我們設定的高度比視訊的高度低的話，為了不讓視訊變形，會將width設值為height * videoWidth / videoHeight，也就是width變小，導致SurfaceView不能佔滿整個螢幕的寬度。

當然你也可以把判斷去掉，這樣無論什麼情況都可以佔滿整個螢幕的寬度。不知道之後會出現什麼情況，所以暫時不改這裡的邏輯。

好了，自定義SurfaceView到這裡！！