android camera2 API流程分析

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() {

        @Override
        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() {

                        @Override
                        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() {

                @Override
                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() {

        @Override
        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 surfaces = new ArrayList();

            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() {

                @Override
                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。