参考官方的VideoView

官方的videoView继承与SurfaceView，它对MediaPlayer进行了一次封装，使用SurfaceView显示MediaPlayer的最少代码：

class videoView extends SurfaceView{
  //构造函数
   
  //增加回调
  getHolder().addCallback(mSHCallback);
  //创建构造的实例 mSHCallback
      private SurfaceHolder.Callback mSHCallback = new SurfaceHolder.Callback() {
        @Override
        public void surfaceCreated(@NonNull SurfaceHolder holder) {
//看一眼mediePlayer需要设置什么setDisplay(holder)
            player.setDisplay(holder);
        }

        @Override
        public void surfaceChanged(@NonNull SurfaceHolder holder, int format, int width, int height) {

        }

        @Override
        public void surfaceDestroyed(@NonNull SurfaceHolder holder) {

        }
    };
}

至于怎么绘制交给了MediaPlayerl来完成了。

VideoView源码

在构造函数中设置了绘制回调和当前focus.

getHolder().addCallback(mSHCallback);
getHolder().setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
setFocusable(true);
setFocusableInTouchMode(true);
requestFocus();

VideoView

    @UnsupportedAppUsage
    SurfaceHolder.Callback mSHCallback = new SurfaceHolder.Callback()
    {
        public void surfaceChanged(SurfaceHolder holder, int format,
                                    int w, int h)
        {
            mSurfaceWidth = w;
            mSurfaceHeight = h;
            //判断状态
            boolean isValidState =  (mTargetState == STATE_PLAYING);
            //视口的大小是不是发生改变了，因为create方法之后就会调用这个方法，如果大小没有发生变化，那么就直接设置 进度就可以了
            boolean hasValidSize = (mVideoWidth == w && mVideoHeight == h);
            if (mMediaPlayer != null && isValidState && hasValidSize) {
                if (mSeekWhenPrepared != 0) {
                    seekTo(mSeekWhenPrepared);
                }
                start();
            }
        }

        public void surfaceCreated(SurfaceHolder holder)
        {
            mSurfaceHolder = holder;
            openVideo();
        }

        public void surfaceDestroyed(SurfaceHolder holder)
        {
            // after we return from this we can't use the surface any more
            mSurfaceHolder = null;
            if (mMediaController != null) mMediaController.hide();
            release(true);
        }
    };

getDefaultSize

返回默认大小

• 如果MeasureSpec 没有施加任何约束，则使用提供的大小。
• 如果 MeasureSpec 允许将变大

参数说明

• size 这个视图的默认大小
• measureSpec 由父级强加的约束
• return 这个视图应该是的大小。

 public static int getDefaultSize(int size, int measureSpec) {
        int result = size;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        switch (specMode) {
        case MeasureSpec.UNSPECIFIED:
            result = size;
            break;
        case MeasureSpec.AT_MOST:
        case MeasureSpec.EXACTLY:
            result = specSize;
            break;
        }
        return result;
    }

onMeasure方法

• 根据宽和高，如果都是固定的，那么就使用比例
• 如果宽固定，那么就按照比例得到高，如果大于限定值就使用限定值
• 高同理
• 宽度和高度都不固定，请尝试使用实际视频大小

 @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int width = getDefaultSize(mVideoWidth, widthMeasureSpec);
        int height = getDefaultSize(mVideoHeight, heightMeasureSpec);
        if (mVideoWidth > 0 && mVideoHeight > 0) {

            int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
            int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);
            int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
            int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);
        //如果宽和高都是固定的，我们根据比例
            if (widthSpecMode == MeasureSpec.EXACTLY && heightSpecMode == MeasureSpec.EXACTLY) {
                // the size is fixed
                width = widthSpecSize;
                height = heightSpecSize;

                // for compatibility, we adjust size based on aspect ratio
                if ( mVideoWidth * height  < width * mVideoHeight ) {
                    //Log.i("@@@", "image too wide, correcting");
                    width = height * mVideoWidth / mVideoHeight;
                } else if ( mVideoWidth * height  > width * mVideoHeight ) {
                    //Log.i("@@@", "image too tall, correcting");
                    height = width * mVideoHeight / mVideoWidth;
                }
            } else if (widthSpecMode == MeasureSpec.EXACTLY) {
                // only the width is fixed, adjust the height to match aspect ratio if possible
                width = widthSpecSize;
                height = width * mVideoHeight / mVideoWidth;
                if (heightSpecMode == MeasureSpec.AT_MOST && height > heightSpecSize) {
                    // couldn't match aspect ratio within the constraints
                    height = heightSpecSize;
                }
            } else if (heightSpecMode == MeasureSpec.EXACTLY) {
                // only the height is fixed, adjust the width to match aspect ratio if possible
                height = heightSpecSize;
                width = height * mVideoWidth / mVideoHeight;
                if (widthSpecMode == MeasureSpec.AT_MOST && width > widthSpecSize) {
                    // couldn't match aspect ratio within the constraints
                    width = widthSpecSize;
                }
            } else {
                // neither the width nor the height are fixed, try to use actual video size
                width = mVideoWidth;
                height = mVideoHeight;
                if (heightSpecMode == MeasureSpec.AT_MOST && height > heightSpecSize) {
                    // too tall, decrease both width and height
                    height = heightSpecSize;
                    width = height * mVideoWidth / mVideoHeight;
                }
                if (widthSpecMode == MeasureSpec.AT_MOST && width > widthSpecSize) {
                    // too wide, decrease both width and height
                    width = widthSpecSize;
                    height = width * mVideoHeight / mVideoWidth;
                }
            }
        } else {
            // no size yet, just adopt the given spec sizes
        }
        setMeasuredDimension(width, height);
    }

设置URI

设置URI，可是URI是什么东西，看一眼源代码：

• URI转换为String

public static String getRealFilePath(final Context context, final Uri uri ) {
        if ( null == uri ) return null;
      //使用的文件格式吧  返回值比如是http  file……
        final String scheme = uri.getScheme();
        String data = null;
        if ( scheme == null )
            data = uri.getPath();
        else if ( ContentResolver.SCHEME_FILE.equals( scheme ) ) {
            data = uri.getPath();
        } else if ( ContentResolver.SCHEME_CONTENT.equals( scheme ) ) {
            Cursor cursor = context.getContentResolver().query( uri, new String[] { MediaStore.Images.ImageColumns.DATA }, null, null, null );
            if ( null != cursor ) {
                if ( cursor.moveToFirst() ) {
                    int index = cursor.getColumnIndex( MediaStore.Images.ImageColumns.DATA );
                    if ( index > -1 ) {
                        data = cursor.getString( index );
                    }
                }
                cursor.close();
            }
        }
        return data;
    }

• setVideoURI(Uri uri,Map<String,String> headers)

* 使用特定标题设置视频 URI。 
* @param uri 视频的 URI。 
* @param headers URI 请求的标头。 
* 请注意，默认情况下允许跨域重定向，但可以通过 headers 参数使用键/值对进行更改，其中 "android-allow-cross-domain-redirect" 作为键和 "0" 或 "1" " 作为值禁止或允许跨域重定向。

openVideo

• 如果没有渲染平面， 或者uri为null的时候返回
• 如果有已经播放的就停止掉
• 创建MediaPlayer
  -设置监听

    public void stopPlayback() {
        if (mMediaPlayer != null) {
            mMediaPlayer.stop();
            mMediaPlayer.release();
            mMediaPlayer = null;
            mCurrentState = STATE_IDLE;
            mTargetState  = STATE_IDLE;
            mAudioManager.abandonAudioFocus(null);
        }
    }

    private void openVideo() {
        if (mUri == null || mSurfaceHolder == null) {
            // not ready for playback just yet, will try again later
            return;
        }
        // we shouldn't clear the target state, because somebody might have
        // called start() previously
        release(false);

        if (mAudioFocusType != AudioManager.AUDIOFOCUS_NONE) {
            // TODO this should have a focus listener
            mAudioManager.requestAudioFocus(null, mAudioAttributes, mAudioFocusType, 0 /*flags*/);
        }

        try {
            mMediaPlayer = new MediaPlayer();
            // TODO: create SubtitleController in MediaPlayer, but we need
            // a context for the subtitle renderers
            final Context context = getContext();
            final SubtitleController controller = new SubtitleController(
                    context, mMediaPlayer.getMediaTimeProvider(), mMediaPlayer);
            controller.registerRenderer(new WebVttRenderer(context));
            controller.registerRenderer(new TtmlRenderer(context));
            controller.registerRenderer(new Cea708CaptionRenderer(context));
            controller.registerRenderer(new ClosedCaptionRenderer(context));
            mMediaPlayer.setSubtitleAnchor(controller, this);

            if (mAudioSession != 0) {
                mMediaPlayer.setAudioSessionId(mAudioSession);
            } else {
                mAudioSession = mMediaPlayer.getAudioSessionId();
            }
            mMediaPlayer.setOnPreparedListener(mPreparedListener);
            mMediaPlayer.setOnVideoSizeChangedListener(mSizeChangedListener);
            mMediaPlayer.setOnCompletionListener(mCompletionListener);
            mMediaPlayer.setOnErrorListener(mErrorListener);
            mMediaPlayer.setOnInfoListener(mInfoListener);
            mMediaPlayer.setOnBufferingUpdateListener(mBufferingUpdateListener);
            mCurrentBufferPercentage = 0;
            mMediaPlayer.setDataSource(mContext, mUri, mHeaders);
            mMediaPlayer.setDisplay(mSurfaceHolder);
            mMediaPlayer.setAudioAttributes(mAudioAttributes);
            mMediaPlayer.setScreenOnWhilePlaying(true);
            mMediaPlayer.prepareAsync();

            for (Pair<InputStream, MediaFormat> pending: mPendingSubtitleTracks) {
                try {
                    mMediaPlayer.addSubtitleSource(pending.first, pending.second);
                } catch (IllegalStateException e) {
                    mInfoListener.onInfo(
                            mMediaPlayer, MediaPlayer.MEDIA_INFO_UNSUPPORTED_SUBTITLE, 0);
                }
            }

            // we don't set the target state here either, but preserve the
            // target state that was there before.
            mCurrentState = STATE_PREPARING;
            attachMediaController();
        } catch (IOException ex) {
            Log.w(TAG, "Unable to open content: " + mUri, ex);
            mCurrentState = STATE_ERROR;
            mTargetState = STATE_ERROR;
            mErrorListener.onError(mMediaPlayer, MediaPlayer.MEDIA_ERROR_UNKNOWN, 0);
            return;
        } catch (IllegalArgumentException ex) {
            Log.w(TAG, "Unable to open content: " + mUri, ex);
            mCurrentState = STATE_ERROR;
            mTargetState = STATE_ERROR;
            mErrorListener.onError(mMediaPlayer, MediaPlayer.MEDIA_ERROR_UNKNOWN, 0);
            return;
        } finally {
            mPendingSubtitleTracks.clear();
        }
    }

这个里面无论用户有没有加监听都会将视频常用的监听加上，用户如果有补充的监听，在通过回调的方式传递进来，在相对应的监听代码里面判断不为null，就进行调用。

@Override
public void onPrepared(MediaPlayer mp) {
      if (preparedListener != null) {
          preparedListener.onPrepared(mp);
      }
}

监听方法

OnPreparedListener

• 先设置进度
• 调用开始
• 改变状态

MediaPlayer.OnPreparedListener mPreparedListener = new MediaPlayer.OnPreparedListener() {
        public void onPrepared(MediaPlayer mp) {
            mCurrentState = STATE_PREPARED;
            if (mOnPreparedListener != null) {
                mOnPreparedListener.onPrepared(mMediaPlayer);
            }
            if (mMediaController != null) {
                mMediaController.setEnabled(true);
            }
            int seekToPosition = mSeekWhenPrepared;  // mSeekWhenPrepared may be changed after seekTo() call
      //我认为这里不需要判断也可以吧。开始的位就是0 ，设置0有什么问题 ？
       if (seekToPosition != 0) {
        seekTo(seekToPosition);
     }
      start();
}