http://blog.csdn.net/wds1181977/article/details/52174840
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.
new format: " + newFormat.toString());
mVideoTrackIndex = mMuxer.addTrack(newFormat);
mMuxer.start();
mMuxerStarted = true;
Log.i(TAG, "started media muxer, videoIndex=" + mVideoTrackIndex);
}