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mp4while (!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 10msThread.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 onceif (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 
本文Demo