android camera2 API流程分析

時間 2019-11-06

標籤 android camera2 camera api 流程分析欄目 Android 简体版

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Android camera2 API流程分析
Android5.0以後，新推出來了一個類，android.hardware.camera2，與原來的camera的類實現照相和拍視頻的流程有所不一樣，原來的camera的類並無深刻分析。在作項目的時候，因爲須要涉及到這方面的知識，本身學了一下。因爲本人英文也不是很優秀，看着看着還要看前人的總結。這個是在半年前就簡單總結了一下，如今po上來。若有錯誤，敬請指教！android

1、整體分析session

Camera2流程示意圖：ide

CameraManager：管理全部的攝像頭（CameraDevice）設備的管理者，打開攝像頭等功能。函數

CameraDevice：一個手機設備通常有兩個攝像頭（CameraDevice），前置和後置。該類經過CameraCharacteristics對象提供攝像頭的硬件信息，配置信息和輸出參數等。ui

CameraCaptureSession:經過CameraDevice 中createCaptureSession(List, CameraCaptureSession.StateCallback, Handler)建立一個CaptureSession會話，全部的CaptureRequest和返回的data都在這個會話中進行。其中，該類中的capture (CaptureRequest request, CameraCaptureSession.CaptureCallback listener, Handler handler)的功能是捕獲一次（one-shot），通常用於照相setRepeatingRequest (CaptureRequest request, CameraCaptureSession.CaptureCallbacklistener, Handler handler)是不停的發出capture的請求，也就是一直在捕獲畫面，通常用於捕獲畫面輸出至預覽界面或者錄製視頻。Capture()比setRepeatingRequest ()優先級高，當在setRepeatingRequest 時進行Capture，會先處理Capture,而後繼續setRepeatingRequest 。（PS:能夠根據平時使用相機時，首先咱們看到的預覽界面是setRepeatingRequest 顯示出來的，當點擊拍照時執行Capture，而後又出現預覽界面繼續實行setRepeatingRequest ）。.net

CameraRequest：request中定義了照相效果的一些參數，而且必須使用addTarget()函數爲這個request添加一個target surface，在最後CameraDevice返回的數據送到這個target surface中。在android camera2的API文檔中，這個target surface能夠是Surface View，Surface Texture，將返回的數據傳遞到預覽界面中；還能夠是MediaRecorder或mageReader，將返回的數據傳給這兩個類，進行進一步處理，造成視頻文件或者圖片。線程

TotalCaptureResult：繼承CaptureResult類，CaptureResult繼承CameraMetadata類。包含camera device的狀態信息。code

2、照相流程分析（參考Camera2Basic）orm

Camera2Basic在顯示預覽界面和拍照時建立了一個session,兩個request，mPreviewRequest和captureBuilder.build()分別將數據返回給預覽界面和Image。視頻

顯示preview的代碼：

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);//根據mCameraId打開前置或者後置攝像頭
//mBackgroundHandler是處理打開攝像頭的線程
//mStateCallback打開攝像頭後，進入這個回調函數
} 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) {//若成功打開，進入這個函數
// This method is called when the camera is opened. We start camera preview here.
mCameraOpenCloseLock.release();
mCameraDevice = cameraDevice;
createCameraPreviewSession();//建立顯示預覽界面的函數
}
//………
}

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爲surface，就是手機的界面

// Here, we create a CameraCaptureSession for camera preview.
mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),//拍照的session，注意這裏有兩個surface
//一個是手機的界面，一個是圖片。
//也就是說，這個session造成的數據流，
//能夠一個傳向手機界面，一個造成圖片
//具體看Caputre()或者SetRepeatingRequest函數裏面的
//參數request的addtarget()裏面的值

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是手機界面的surface，就是造成預覽
//所以須要setRepeatingRequest，持續捕獲幀造成視頻
mCaptureCallback, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}

//……….
}

CameraDevice.StateCallback：

當CameraDevice狀態改變（打開或關閉）後調用該函數，通常在該函數執行以下功能：

建立CameraDevice.TEMPLATE_PREVIEW類型的previewRequest，設置addTarget()爲preview的surface。

建立session，這個session有兩個request，所以要把request的target surface都放到List中，createCaptureSession(List, CameraCaptureSession.StateCallback, Handler)中的List爲preview和ImageReader的surface。CameraCaptureSession.StateCallback裏面進行setRepeatingCapture()，將捕獲的畫面顯示在preview上。mCaptureCallback說是捕獲完成後的回調函數，暫不分析。

拍照（捕獲靜態圖像）的代碼：

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();//停掉以前的setrepeating的持續不斷的捕獲
mCaptureSession.capture(captureBuilder.build(), CaptureCallback, null);//capture的時候，數據流造成image
} catch (CameraAccessException e) {
e.printStackTrace();
}
}

相似上述分析，不過此時request的類型cameraDevice.TEMPLATE_STILL_CAPTURE而且addTarget()的對象ImageReader，另外setRepeatingCapture換成了capture。即捕獲一個frame，返回至ImageReader中造成圖片。

3、錄像流程分析（參考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];//後置攝像頭的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);//打開相機，進入回調函數
//……
}

private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {

@Override
public void onOpened(CameraDevice cameraDevice) {
mCameraDevice = cameraDevice;
startPreview(); //進入這個函數
mCameraOpenCloseLock.release();
if (null != mTextureView) {
configureTransform(mTextureView.getWidth(), mTextureView.getHeight());
}
}
//……
}

private void startPreview() {
if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
return;
}
try {
setUpMediaRecorder();//設置mediarecoder的參數，具體的介紹看android developer文檔
SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);//此時request的參數是record
List<Surface> surfaces = new ArrayList<Surface>();

Surface previewSurface = new Surface(texture);
surfaces.add(previewSurface);
mPreviewBuilder.addTarget(previewSurface);//target是預覽界面

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();//進入這個函數
}

//……….
}, mBackgroundHandler);}

//此爲mediaRecoder的設置，具體見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發送請求，持續捕獲幀
} catch (CameraAccessException e) {
e.printStackTrace();
}
}

//進行上面設置以後，點擊button，執行startRecordingVideo（）函數，mMediaRecorder.start();開始錄製視頻

private void startRecordingVideo() {
try {
// UI
mButtonVideo.setText(R.string.stop);
mIsRecordingVideo = true;

// Start recording
mMediaRecorder.start();
} catch (IllegalStateException e) {
e.printStackTrace();
}
}
//再次點擊button，中止錄製。源代碼會出現一些問題，應該先關閉capture以後再中止錄製，具體問題在stackoverflow裏面有寫。

private void stopRecordingVideo() {
// UI
mIsRecordingVideo = false;
mButtonVideo.setText(R.string.record);
//modifying!!!!~~~~~android官方的demo裏面在中止拍攝的時候會卡，因此改了一點
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();//最後執行這個函數，從新開始預覽，準備錄製視頻
}
}

在Camera2Video中：只建立了一個session，一個request有兩個target surface-MediaRecorder和Preview。SetRepeatingRequest()不停的捕獲畫面一方面顯示在preview上，另外一方面造成視頻流。當MediaRecorder.start()時，開始錄製，以前SetRepeatingRequest的幀（frame）拋棄掉，從start開始幀輸出到指定的文件中。

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