MediaProjection介绍

MediaProjection可以用来捕捉屏幕，具体来说可以截取当前屏幕和录制屏幕视频。MediaProjection由MediaProjectionManager来管理和获取。

使用步骤

首先获取MediaProjectionManager，和其他的Manager一样通过 Context.getSystemService() 传入参数MEDIA_PROJECTION_SERVICE获得实例。

接着调用MediaProjectionManager.createScreenCaptureIntent()弹出dialog询问用户是否授权应用捕捉屏幕，同时覆写onActivityResult()获取授权结果。

如果授权成功，通过MediaProjectionManager.getMediaProjection(int resultCode, Intent resultData)获取MediaProjection实例，通过MediaProjection.createVirtualDisplay(String name, int width, int height, int dpi, int flags, Surface surface, VirtualDisplay.Callback callback, Handler handler)创建VirtualDisplay实例。实际上在上述方法中传入的surface参数，是真正用来截屏或者录屏的。

截屏

截屏这里用到ImageReader类，这个类的getSurface()方法获取到surface直接传入MediaProjection.createVirtualDisplay()方法中，此时就可以执行截取。通过ImageReader.acquireLatestImage()方法即可获取当前屏幕的Image，经过简单处理之后即可保存为Bitmap。

           private void startCapture() {

            mImageName = System.currentTimeMillis() + ".png";

            Log.e(TAG, "image name is : " + mImageName);

            Image image = mImageReader.acquireLatestImage();

            int width = image.getWidth();

            int height = image.getHeight();

            final Image.Plane[] planes = image.getPlanes();

            final ByteBuffer buffer = planes[0].getBuffer();

            int pixelStride = planes[0].getPixelStride();

            int rowStride = planes[0].getRowStride();

            int rowPadding = rowStride - pixelStride * width;

            Bitmap bitmap = Bitmap.createBitmap(width + rowPadding / pixelStride, height, Bitmap.Config.ARGB_8888);

            bitmap.copyPixelsFromBuffer(buffer);

            bitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height);

            image.close();

            if (bitmap != null) {

                Log.e(TAG, "bitmap  create success ");

                try {

                    File fileFolder = new File(mImagePath);

                    if (!fileFolder.exists())

                        fileFolder.mkdirs();

                    File file = new File(mImagePath, mImageName);

                    if (!file.exists()) {

                        Log.e(TAG, "file create success ");

                        file.createNewFile();

                    }

                    FileOutputStream out = new FileOutputStream(file);

                    bitmap.compress(Bitmap.CompressFormat.PNG, 100, out);

                    out.flush();

                    out.close();

                    Log.e(TAG, "file save success ");

                    Toast.makeText(this.getApplicationContext(), "截图成功", Toast.LENGTH_SHORT).show();

                } catch (IOException e) {

                    Log.e(TAG, e.toString());

                    e.printStackTrace();

                }

            }

        }

录屏

录屏需要用到上篇博文中的MediaCadec，这个类将原始的屏幕数据编码，在通过MediaMuxer分装为mp4格式保存。MediaCodec.createInputSurface()获取一个surface对象讲起传入MediaProjection.createVirtualDisplay()即可获取屏幕原始多媒体数据，之后读取MediaCodec编码输出数据经过MediaMuxer封装处理为mp4即可播放，实现录屏。

       private void recordVirtualDisplay() {//循环多去编解码器输出数据经过处理保存为mp4

        while (!mIsQuit.get()) {

            int index = mMediaCodec.dequeueOutputBuffer(mBufferInfo, 10000);

            Log.i(TAG, "dequeue output buffer index=" + index);

            if (index == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {//后续输出格式变化

                resetOutputFormat();

            } else if (index == MediaCodec.INFO_TRY_AGAIN_LATER) {//请求超时

                Log.d(TAG, "retrieving buffers time out!");

                try {

                    // wait 10ms

                    Thread.sleep(10);

                } catch (InterruptedException e) {

                }

            } else if (index >= 0) {//有效输出

                if (!mMuxerStarted) {

                    throw new IllegalStateException("MediaMuxer dose not call addTrack(format) ");

                }

                encodeToVideoTrack(index);

                mMediaCodec.releaseOutputBuffer(index, false);

            }

        }

    }

        private void encodeToVideoTrack(int index) {//输出数据为mp4文件

        ByteBuffer encodedData = mMediaCodec.getOutputBuffer(index);

        if ((mBufferInfo.flags & MediaCodec.BUFFER_FLAG_CODEC_CONFIG) != 0) {//是特定格式信息等配置数据，不是媒体数据

            // The codec config data was pulled out and fed to the muxer when we got

            // the INFO_OUTPUT_FORMAT_CHANGED status.

            // Ignore it.

            Log.d(TAG, "ignoring BUFFER_FLAG_CODEC_CONFIG");

            mBufferInfo.size = 0;

        }

        if (mBufferInfo.size == 0) {

            Log.d(TAG, "info.size == 0, drop it.");

            encodedData = null;

        } else {

            Log.d(TAG, "got buffer, info: size=" + mBufferInfo.size

                    + ", presentationTimeUs=" + mBufferInfo.presentationTimeUs

                    + ", offset=" + mBufferInfo.offset);

        }

        if (encodedData != null) {//存在编码数据

            encodedData.position(mBufferInfo.offset);

            encodedData.limit(mBufferInfo.offset + mBufferInfo.size);

            mMuxer.writeSampleData(mVideoTrackIndex, encodedData, mBufferInfo);//写入

            Log.i(TAG, "sent " + mBufferInfo.size + " bytes to muxer...");

        }

    }

        private void resetOutputFormat() {

        // should happen before receiving buffers, and should only happen once

        if (mMuxerStarted) {

            throw new IllegalStateException("output format already changed!");

        }

        MediaFormat newFormat = mMediaCodec.getOutputFormat();

        Log.i(TAG, "output format changed.\n new format: " + newFormat.toString());

        mVideoTrackIndex = mMuxer.addTrack(newFormat);

        mMuxer.start();

        mMuxerStarted = true;

        Log.i(TAG, "started media muxer, videoIndex=" + mVideoTrackIndex);

    }

附录参考

官方文档

Android视频录制

Android 5.0截屏

Android录屏代码 
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