这是Android音视频的第一篇文章，终于回到了我的老本行上。之前好像从来没有做过Camera相关的开发，这块对我来说还是有点陌生，所以从头开始学起。
Camera2
在Android API21中Google发布了Camera2来取代原本的Camera，两者的变动也是比较大的。
image
Camera2中Google采用了pipeline（管道）的概念，将Camera Device相机设备和Android Device安卓设备连接起来， Android Device通过管道发送CaptureRequest请求给Camera Device，Camera Device通过管道返回CameraMetadata数据给Android Device，这一切建立在一个叫作CameraCaptureSession的会话中。
Camera2主要类说明
在Camera2 架构在核心参与类角色有：CameraManager、CameraDevice、CameraCharacteristics、CameraRequest与CameraRequest.Builder、CameraCaptureSession以及CaptureResult。
CameraManager
位于android.hardware.camera2.CameraManager下，也是Android 21(5.0)添加的，和其他系统服务一样通过 Context.getSystemService(Context.CAMERA_SERVICE) 来完成初始化，主要用于管理系统摄像头。
-
manager.getCameraIdList()获取Android设备的摄像头列表 -
manager.getCameraCharacteristics(cameraId)获取指定摄像头的相关特性 -
manager.openCamera(String cameraId, CameraDevice.StateCallback callback, Handler handler)打开指定Id的摄像头，StateCallback 是打开状态的一个监听回调，Handler 表示使用哪个线程处理回调，如果为null则表示当前线程。
CameraDevice
CameraDevice是Camera2抽象出来的一个对象，直接与系统硬件摄像头相联系。
-
通过CameraDevice.StateCallback监听摄像头的状态
private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback(){ @Override public void onOpened(@NonNull CameraDevice camera) { //摄像头打开，可以创建会话，开始预览 } @Override public void onDisconnected(@NonNull CameraDevice camera) { } @Override public void onError(@NonNull CameraDevice camera, int error) { } }; 管理CameraCaptureSession会话，相当于Android Device和Camera Device之间的管道，后面的数据交流都在这个会话中完成。
管理CaptureRequest，主要包括通过createCaptureRequest（int templateType）创建捕获请求，在需要预览、拍照、再次预览的时候都需要通过创建请求来完成。
CameraCaptureSession
正如前面所说，系统向摄像头发送 Capture 请求，而摄像头会返回 CameraMetadata，这一切都是在由对应的CameraDevice创建的CameraCaptureSession 会话完成，当程序需要预览、拍照、再次预览时，都需要先通过会话。CameraCaptureSession一旦被创建，直到对应的CameraDevice关闭才会死掉。虽然CameraCaptureSession会话用于从摄像头中捕获图像，但是只有同一个会话才能再次从同一摄像头中捕获图像。
- 管理CameraCaptureSession.StateCallback状态回调，用于接收有关CameraCaptureSession状态的更新的回调对象，主要回调方法有两个当CameraDevice 完成配置，对应的会话开始处理捕获请求时触发onConfigured(CameraCaptureSession session)方法，反之配置失败时候触发onConfigureFailed(CameraCaptureSession session)方法。
- 管理CameraCaptureSession.CaptureCallback捕获回调，用于接收捕获请求状态的回调，当请求触发捕获已启动时、捕获完成时、在捕获图像时发生错误的情况下都会触发该回调对应的方法。
- 通过调用方法capture(CaptureRequest request, CameraCaptureSession.CaptureCallback listener, Handler handler)提交捕获图像请求，即拍照。
- 通过调用方法setRepeatingRequest(CaptureRequest request, CameraCaptureSession.CaptureCallback listener, Handler handler)请求不断重复捕获图像，即实现预览。
- 通过方法调用stopRepeating()实现停止捕获图像，即停止预览。
CameraCharacteristics
描述Cameradevice属性的对象，可以使用CameraManager通过getCameraCharacteristics（String cameraId）进行查询。
CameraRequest与CameraRequest.Builder
CameraRequest代表了一次捕获请求
CameraRequest.Builder用于描述捕获图片的各种参数设置，包含捕获硬件（传感器，镜头，闪存），对焦模式、曝光模式，处理流水线，控制算法和输出缓冲区的配置，然后传递到对应的会话中进行设置。CameraRequest.Builder负责生成CameraRequest对象。
CaptureResult
CaptureRequest描述是从图像传感器捕获单个图像的结果的子集的对象。
代码实现
谷歌有写两个示例程序，介绍如何使用Camera2
android-Camera2Basic
android-Camera2Video
示例程序中有预览、拍照、录像等功能，非常好的入门学习代码。
在这里还是过一遍整个流程，加深理解。
1、打开摄像头
private void openCamera(int width, int height) {
// 判断权限
if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.CAMERA)
!= PackageManager.PERMISSION_GRANTED) {
requestCameraPermission();
return;
}
// 设置参数，获取摄像头ID、设置预览宽高等
setUpCameraOutputs(width, height);
// 配置TextureView的纹理转换，解决Camera显示变形问题
configureTransform(width, height);
Activity activity = getActivity();
CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
try {
//Semaphore 信号量，保证只能有一条线程使用Camera设备
if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
throw new RuntimeException("Time out waiting to lock camera opening.");
}
//真正去打开摄像头，在mStateCallback中获取成功或失败的回调
manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
} 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(@NonNull CameraDevice cameraDevice) {
// This method is called when the camera is opened. We start camera preview here.
mCameraOpenCloseLock.release();
mCameraDevice = cameraDevice;
//创建会话，开始预览
createCameraPreviewSession();
}
@Override
public void onDisconnected(@NonNull CameraDevice cameraDevice) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
}
@Override
public void onError(@NonNull CameraDevice cameraDevice, int error) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
Activity activity = getActivity();
if (null != activity) {
activity.finish();
}
}
};
2、创建会话，开始预览
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);
//这里是指实时图像数据的输出目标，以后录制视频、直播等都需要在这里添加对应的Target
mPreviewRequestBuilder.addTarget(surface);
// Here, we create a CameraCaptureSession for camera preview.
mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
// The camera is already closed
if (null == mCameraDevice) {
return;
}
// When the session is ready, we start displaying the preview.
mCaptureSession = cameraCaptureSession;
try {
// 设置自动对焦
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
// Flash is automatically enabled when necessary.
setAutoFlash(mPreviewRequestBuilder);
// Finally, we start displaying the camera preview.
mPreviewRequest = mPreviewRequestBuilder.build();
//不断捕获图像，显示预览图像
mCaptureSession.setRepeatingRequest(mPreviewRequest,
mCaptureCallback, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
@Override
public void onConfigureFailed(
@NonNull CameraCaptureSession cameraCaptureSession) {
showToast("Failed");
}
}, null
);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
3、拍照
/**
* Initiate a still image capture.
*/
private void takePicture() {
lockFocus();
}
/**
* Lock the focus as the first step for a still image capture.
*/
private void lockFocus() {
try {
// 告诉摄像机开始对焦
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
CameraMetadata.CONTROL_AF_TRIGGER_START);
// Tell #mCaptureCallback to wait for the lock.
mState = STATE_WAITING_LOCK;
// 发送CaptureRequest要求摄像机捕捉图像
mCaptureSession.capture(mPreviewRequestBuilder.build(), mCaptureCallback,
mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private CameraCaptureSession.CaptureCallback mCaptureCallback
= new CameraCaptureSession.CaptureCallback() {
private void process(CaptureResult result) {
//处理对焦、闪光灯等
.......
case STATE_WAITING_LOCK: {
.......
//对焦完成，保存一张图片
captureStillPicture()；
.......
break;
}
}
}
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.
// 将mImageReader作为目标，获得的图片数据会交给mImageReader处理
// 初始化时 mImageReader.setOnImageAvailableListener(mOnImageAvailableListener, mBackgroundHandler);
// 所以数据最终会在mOnImageAvailableListener中处理
final CaptureRequest.Builder captureBuilder =
mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
captureBuilder.addTarget(mImageReader.getSurface());
// Use the same AE and AF modes as the preview.
captureBuilder.set(CaptureRequest.CONTROL_AF_MODE,
CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
setAutoFlash(captureBuilder);
// Orientation
int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));
// 拍照事件的最终回调，图片处理完后调用onCaptureCompleted
CameraCaptureSession.CaptureCallback CaptureCallback
= new CameraCaptureSession.CaptureCallback() {
@Override
public void onCaptureCompleted(@NonNull CameraCaptureSession session,
@NonNull CaptureRequest request,
@NonNull TotalCaptureResult result) {
showToast("Saved: " + mFile);
Log.d(TAG, mFile.toString());
unlockFocus();
}
};
mCaptureSession.stopRepeating();
mCaptureSession.abortCaptures();
mCaptureSession.capture(captureBuilder.build(), CaptureCallback, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
// 数据处理、保存
private final ImageReader.OnImageAvailableListener mOnImageAvailableListener
= new ImageReader.OnImageAvailableListener() {
@Override
public void onImageAvailable(ImageReader reader) {
//mBackgroundHandler.post(new ImageSaver(reader.acquireNextImage(), mFile));
Image mImage = reader.acquireNextImage();
ByteBuffer buffer = mImage.getPlanes()[0].getBuffer();
byte[] bytes = new byte[buffer.remaining()];
buffer.get(bytes);
// 文件操作
// ......
// 这里获取到的是视频的原始数据，要对数据做进一步的算法处理、或者采用第三方的编码库进行压缩、以及网络传输等，都可以从这里拿到数据。
mImage.close()；
}
};
4、录像
主要看一下MediaRecorder录制视频相关代码
private void startRecordingVideo() {
if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
return;
}
try {
// 关闭之前的会话，新的会话会添加录像的Target
closePreviewSession();
// 配置MediaRecorder，音频、视频来源，编码格式等
setUpMediaRecorder();
SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
// 创建一个适合视频录制的请求
mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);
List surfaces = new ArrayList<>();
// Set up Surface for the camera preview
Surface previewSurface = new Surface(texture);
surfaces.add(previewSurface);
mPreviewBuilder.addTarget(previewSurface);
// Set up Surface for the MediaRecorder 重要的一步，视频信息会交给mMediaRecorder处理
Surface recorderSurface = mMediaRecorder.getSurface();
surfaces.add(recorderSurface);
mPreviewBuilder.addTarget(recorderSurface);
// Start a capture session
// Once the session starts, we can update the UI and start recording
mCameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
mPreviewSession = cameraCaptureSession;
updatePreview();
getActivity().runOnUiThread(new Runnable() {
@Override
public void run() {
// UI
mButtonVideo.setText(R.string.stop);
mIsRecordingVideo = true;
// 开始录制
mMediaRecorder.start();
}
});
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
Activity activity = getActivity();
if (null != activity) {
Toast.makeText(activity, "Failed", Toast.LENGTH_SHORT).show();
}
}
}, mBackgroundHandler);
} catch (CameraAccessException | IOException e) {
e.printStackTrace();
}
}
// 配置MediaRecorder
private void setUpMediaRecorder() throws IOException {
final Activity activity = getActivity();
if (null == activity) {
return;
}
// 设置要用于录制的音频源。
mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
// 设置要用于录制的视频源。
mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
// 设置录制期间生成的输出文件的格式。
mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
// 生成MP4文件路径
if (mNextVideoAbsolutePath == null || mNextVideoAbsolutePath.isEmpty()) {
mNextVideoAbsolutePath = getVideoFilePath(getActivity());
}
mMediaRecorder.setOutputFile(mNextVideoAbsolutePath);
// 设置用于录制的视频编码比特率。
mMediaRecorder.setVideoEncodingBitRate(10000000);
// 设置要捕获的视频的帧速率。
mMediaRecorder.setVideoFrameRate(30);
mMediaRecorder.setVideoSize(mVideoSize.getWidth(), mVideoSize.getHeight());
// 设置要用于录制的视频编码器。
mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
// 设置要用于录制的音频编码器。
mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
switch (mSensorOrientation) {
case SENSOR_ORIENTATION_DEFAULT_DEGREES:
mMediaRecorder.setOrientationHint(DEFAULT_ORIENTATIONS.get(rotation));
break;
case SENSOR_ORIENTATION_INVERSE_DEGREES:
mMediaRecorder.setOrientationHint(INVERSE_ORIENTATIONS.get(rotation));
break;
}
// 在调用start前必须的一步
mMediaRecorder.prepare();
}
/**
* 常规使用MediaRecorder去录制视频的例子如下：
* MediaRecorder recorder = new MediaRecorder();
* recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
* recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
* recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
* recorder.setOutputFile(PATH_NAME);
* recorder.prepare();
* recorder.start(); // Recording is now started
* ...
* recorder.stop();
* recorder.reset(); // You can reuse the object by going back to setAudioSource() step
* recorder.release(); // Now the object cannot be reused
**/
Camera2预览、拍照和录像的大概流程就是这样，相对来说挺复杂的，但也非常重要，后面会继续深入分析原理和源码。