Android camera2 API流程分析
Android5.0之后,新推出来了一个类,android.hardware.camera2,与原来的camera的类实现照相和拍视频的流程有所不同,原来的camera的类并没有深入分析。在做项目的时候,由于需要涉及到这方面的知识,自己学了一下。由于本人英文也不是很优秀,看着看着还要看前人的总结。这个是在半年前就简单总结了一下,现在po上来。如有错误,敬请指教!一、总体分析
Camera2流程示意图: CameraManager:管理所有的摄像头(CameraDevice)设备的管理者,打开摄像头等功能。
CameraDevice:一个手机设备一般有两个摄像头(CameraDevice),前置和后置。该类通过CameraCharacteristics对象提供摄像头的硬件信息,配置信息和输出参数等。
CameraCaptureSession:通过CameraDevice 中createCaptureSession(List, CameraCaptureSession.StateCallback, Handler)创建一个CaptureSession会话,所有的CaptureRequest和返回的data都在这个会话中进行。其中,该类中的capture (CaptureRequest request, CameraCaptureSession.CaptureCallback listener, Handler handler)的功能是捕获一次(one-shot),一般用于照相setRepeatingRequest (CaptureRequest request, CameraCaptureSession.CaptureCallbacklistener, Handler handler)是不停的发出capture的请求,也就是一直在捕获画面,一般用于捕获画面输出至预览界面或者录制视频。Capture()比setRepeatingRequest ()优先级高,当在setRepeatingRequest 时进行Capture,会先处理Capture,然后继续setRepeatingRequest 。(PS:可以根据平时使用相机时,首先我们看到的预览界面是setRepeatingRequest 显示出来的,当点击拍照时执行Capture,然后又出现预览界面继续实行setRepeatingRequest )。
CameraRequest:request中定义了照相效果的一些参数,并且必须使用addTarget()函数为这个request添加一个target surface,在最后CameraDevice返回的数据送到这个target surface中。在android camera2的API文档中,这个target surface可以是Surface View,Surface Texture,将返回的数据传递到预览界面中;还可以是MediaRecorder或mageReader,将返回的数据传给这两个类,进行进一步处理,形成视频文件或者图片。
TotalCaptureResult:继承CaptureResult类,CaptureResult继承CameraMetadata类。包含camera device的状态信息。
二、照相流程分析(参考Camera2Basic) Camera2Basic在显示预览界面和拍照时创建了一个session,两个request,mPreviewRequest和captureBuilder.build()分别将数据返回给预览界面和Image。 显示preview的代码: private void openCamera(int width, int height) { setUpCameraOutputs(width, height); configureTransform(width, height); Activity activity = getActivity(); CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE); try { if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) { throw new RuntimeException("Time out waiting to lock camera opening."); } manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);//根据mCameraId打开前置或者后置摄像头 //mBackgroundHandler是处理打开摄像头的线程 //mStateCallback打开摄像头后,进入这个回调函数 } catch (CameraAccessException e) { e.printStackTrace(); } catch (InterruptedException e) { throw new RuntimeException("Interrupted while trying to lock camera opening.", e); } } private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() { public void onOpened(CameraDevice cameraDevice) {//若成功打开,进入这个函数 // This method is called when the camera is opened. We start camera preview here. mCameraOpenCloseLock.release(); mCameraDevice = cameraDevice; createCameraPreviewSession();//创建显示预览界面的函数 } //……… } private void createCameraPreviewSession() { try { SurfaceTexture texture = mTextureView.getSurfaceTexture(); assert texture != null; // We configure the size of default buffer to be the size of camera preview we want. texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight()); // This is the output Surface we need to start preview. Surface surface = new Surface(texture); // We set up a CaptureRequest.Builder with the output Surface. mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW); mPreviewRequestBuilder.addTarget(surface);//target为surface,就是手机的界面 // Here, we create a CameraCaptureSession for camera preview. mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),//拍照的session,注意这里有两个surface //一个是手机的界面,一个是图片。 //也就是说,这个session形成的数据流, //可以一个传向手机界面,一个形成图片 //具体看Caputre()或者SetRepeatingRequest函数里面的 //参数request的addtarget()里面的值 new CameraCaptureSession.StateCallback() { public void onConfigured(CameraCaptureSession cameraCaptureSession) { // The camera is already closed if (null == mCameraDevice) { return; } // When the session is ready, we start displaying the preview. mCaptureSession = cameraCaptureSession; try { // Auto focus should be continuous for camera preview. mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE); // Flash is automatically enabled when necessary. mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH); // Finally, we start displaying the camera preview. mPreviewRequest = mPreviewRequestBuilder.build(); mCaptureSession.setRepeatingRequest(mPreviewRequest,//mPreviewRequest的target是手机界面的surface,就是形成预览 //因此需要setRepeatingRequest,持续捕获帧形成视频 mCaptureCallback, mBackgroundHandler); } catch (CameraAccessException e) { e.printStackTrace(); } } //………. }CameraDevice.StateCallback:
当CameraDevice状态改变(打开或关闭)后调用该函数,一般在该函数执行如下功能:
创建CameraDevice.TEMPLATE_PREVIEW类型的previewRequest,设置addTarget()为preview的surface。
创建session,这个session有两个request,因此要把request的target surface都放到List中,createCaptureSession(List, CameraCaptureSession.StateCallback, Handler)中的List为preview和ImageReader的surface。CameraCaptureSession.StateCallback里面进行setRepeatingCapture(),将捕获的画面显示在preview上。mCaptureCallback说是捕获完成后的回调函数,暂不分析。
拍照(捕获静态图像)的代码:
private void captureStillPicture() {
try { final Activity activity = getActivity(); if (null == activity || null == mCameraDevice) { return; } // This is the CaptureRequest.Builder that we use to take a picture. final CaptureRequest.Builder captureBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE); captureBuilder.addTarget(mImageReader.getSurface()); //target是image // Use the same AE and AF modes as the preview. captureBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE); captureBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH); // Orientation int rotation = activity.getWindowManager().getDefaultDisplay().getRotation(); captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation)); CameraCaptureSession.CaptureCallback CaptureCallback = new CameraCaptureSession.CaptureCallback() { public void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request, TotalCaptureResult result) { showToast("Saved: " + mFile); unlockFocus(); } }; mCaptureSession.stopRepeating();//停掉之前的setrepeating的持续不断的捕获 mCaptureSession.capture(captureBuilder.build(), CaptureCallback, null);//capture的时候,数据流形成image } catch (CameraAccessException e) { e.printStackTrace(); } }类似上述分析,不过此时request的类型cameraDevice.TEMPLATE_STILL_CAPTURE并且addTarget()的对象ImageReader,另外setRepeatingCapture换成了capture。即捕获一个frame,返回至ImageReader中形成图片。
三、录像流程分析(参考Camera2Video) private void openCamera(int width, int height) { final Activity activity = getActivity(); if (null == activity || activity.isFinishing()) { return; } CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE); try { if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) { throw new RuntimeException("Time out waiting to lock camera opening."); } String cameraId = manager.getCameraIdList()[0];//后置摄像头的id // Choose the sizes for camera preview and video recording CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId); StreamConfigurationMap map = characteristics .get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP); mVideoSize = chooseVideoSize(map.getOutputSizes(MediaRecorder.class)); mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class), width, height, mVideoSize); int orientation = getResources().getConfiguration().orientation; if (orientation == Configuration.ORIENTATION_LANDSCAPE) { mTextureView.setAspectRatio(mPreviewSize.getWidth(), mPreviewSize.getHeight()); } else { mTextureView.setAspectRatio(mPreviewSize.getHeight(), mPreviewSize.getWidth()); } configureTransform(width, height); mMediaRecorder = new MediaRecorder(); manager.openCamera(cameraId, mStateCallback, null);//打开相机,进入回调函数 //…… } private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() { public void onOpened(CameraDevice cameraDevice) { mCameraDevice = cameraDevice; startPreview(); //进入这个函数 mCameraOpenCloseLock.release(); if (null != mTextureView) { configureTransform(mTextureView.getWidth(), mTextureView.getHeight()); } } //…… } private void startPreview() { if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) { return; } try { setUpMediaRecorder();//设置mediarecoder的参数,具体的介绍看android developer文档 SurfaceTexture texture = mTextureView.getSurfaceTexture(); assert texture != null; texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight()); mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);//此时request的参数是record List<Surface> surfaces = new ArrayList<Surface>(); Surface previewSurface = new Surface(texture); surfaces.add(previewSurface); mPreviewBuilder.addTarget(previewSurface);//target是预览界面 Surface recorderSurface = mMediaRecorder.getSurface(); surfaces.add(recorderSurface); mPreviewBuilder.addTarget(recorderSurface);//target是mediarecorder mCameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() { public void onConfigured(CameraCaptureSession cameraCaptureSession) { mPreviewSession = cameraCaptureSession; updatePreview();//进入这个函数 } //………. }, mBackgroundHandler);} //此为mediaRecoder的设置,具体见MediaRecorder private void setUpMediaRecorder() throws IOException { final Activity activity = getActivity(); if (null == activity) { return; } mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC); mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE); mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4); mMediaRecorder.setOutputFile(getVideoFile(activity).getAbsolutePath()); mMediaRecorder.setVideoEncodingBitRate(10000000); mMediaRecorder.setVideoFrameRate(30); mMediaRecorder.setVideoSize(mVideoSize.getWidth(), mVideoSize.getHeight()); mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264); mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC); int rotation = activity.getWindowManager().getDefaultDisplay().getRotation(); int orientation = ORIENTATIONS.get(rotation); mMediaRecorder.setOrientationHint(orientation); mMediaRecorder.prepare(); } private void updatePreview() { if (null == mCameraDevice) { return; } try { setUpCaptureRequestBuilder(mPreviewBuilder); mPreviewSession.setRepeatingRequest(mPreviewBuilder.build(), null, mBackgroundHandler);//session发送请求,持续捕获帧 } catch (CameraAccessException e) { e.printStackTrace(); } } //进行上面设置之后,点击button,执行startRecordingVideo()函数,mMediaRecorder.start();开始录制视频 private void startRecordingVideo() { try { // UI mButtonVideo.setText(R.string.stop); mIsRecordingVideo = true; // Start recording mMediaRecorder.start(); } catch (IllegalStateException e) { e.printStackTrace(); } } //再次点击button,停止录制。源代码会出现一些问题,应该先关闭capture之后再停止录制,具体问题在stackoverflow里面有写。 private void stopRecordingVideo() { // UI mIsRecordingVideo = false; mButtonVideo.setText(R.string.record); //modifying!!!!~~~~~android官方的demo里面在停止拍摄的时候会卡,所以改了一点 try { // Abort all pending captures. cameraCaptureSession.abortCaptures(); } catch (CameraAccessException e) { e.printStackTrace(); } // Stop recording mMediaRecorder.stop(); mMediaRecorder.reset(); Activity activity = getActivity(); if (null != activity) { Toast.makeText(activity, "Video saved: " + getVideoFile(activity), Toast.LENGTH_SHORT).show(); } startPreview();//最后执行这个函数,重新开始预览,准备录制视频 } } 在Camera2Video中:只创建了一个session,一个request有两个target surface-MediaRecorder和Preview。SetRepeatingRequest()不停的捕获画面一方面显示在preview上,另一方面形成视频流。当MediaRecorder.start()时,开始录制,之前SetRepeatingRequest的帧(frame)抛弃掉,从start开始帧输出到指定的文件中。