问题
My problem is this: I want a background service, that will obtain frames from the camera in real-time, so that I can analyze them. I've seen a lot of similar topics here that supposedly address this issue, but none of them has really worked in my case.
My first attempt was to create an Activity, which started a Service, and inside the service I created a surfaceView, from which I got a holder and implemented a callback to it in which I prepared the camera and everything. Then, on a previewCallback, I could make a new thread, which could analyze the data I was getting from the onPreviewFrame method of PreviewCallback.
That worked well enough, while I had that service in the foreground, but as soon as I opened up another application (with the service still running in the background), I realized that the preview wasn't there so I couldn't get the frames from it.
Searching on the internet, I found out I could perhaps solve this with SurfaceTexture. So, I created an Activity which'd start my service, like this:
public class SurfaceTextureActivity extends Activity {
public static TextureView mTextureView;
public static Vibrator mVibrator;
public static GLSurfaceView mGLView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mGLView = new GLSurfaceView(this);
mTextureView = new TextureView(this);
setContentView(mTextureView);
try {
Intent intent = new Intent(SurfaceTextureActivity.this, RecorderService.class);
intent.putExtra(RecorderService.INTENT_VIDEO_PATH, "/folder-path/");
startService(intent);
Log.i("ABC", "Start Service "+this.toString()+" + "+mTextureView.toString()+" + "+getWindowManager().toString());
}
catch (Exception e) {
Log.i("ABC", "Exc SurfaceTextureActivity: "+e.getMessage());
}
}
}
And then I made the RecorderService implement SurfaceTextureListener, so that I could open the camera and do the other preparations, and then perhaps capture the frames. My RecorderService currently looks like this:
public class RecorderService extends Service implements TextureView.SurfaceTextureListener, SurfaceTexture.OnFrameAvailableListener {
private Camera mCamera = null;
private TextureView mTextureView;
private SurfaceTexture mSurfaceTexture;
private float[] mTransformMatrix;
private static IMotionDetection detector = null;
public static Vibrator mVibrator;
@Override
public void onCreate() {
try {
mTextureView = SurfaceTextureActivity.mTextureView;
mTextureView.setSurfaceTextureListener(this);
Log.i("ABC","onCreate");
// startForeground(START_STICKY, new Notification()); - doesn't work
} catch (Exception e) {
Log.i("ABC","onCreate exception "+e.getMessage());
e.printStackTrace();
}
}
@Override
public void onFrameAvailable(SurfaceTexture surfaceTexture)
{
//How do I obtain frames?!
// SurfaceTextureActivity.mGLView.queueEvent(new Runnable() {
//
// @Override
// public void run() {
// mSurfaceTexture.updateTexImage();
//
// }
// });
}
@Override
public void onSurfaceTextureAvailable(SurfaceTexture surface, int width,
int height) {
mSurfaceTexture = surface;
mSurfaceTexture.setOnFrameAvailableListener(this);
mVibrator = (Vibrator)this.getSystemService(VIBRATOR_SERVICE);
detector = new RgbMotionDetection();
int cameraId = 0;
Camera.CameraInfo info = new Camera.CameraInfo();
for (cameraId = 0; cameraId < Camera.getNumberOfCameras(); cameraId++) {
Camera.getCameraInfo(cameraId, info);
if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT)
break;
}
mCamera = Camera.open(cameraId);
Matrix transform = new Matrix();
Camera.Size previewSize = mCamera.getParameters().getPreviewSize();
int rotation = ((WindowManager)(getSystemService(Context.WINDOW_SERVICE))).getDefaultDisplay()
.getRotation();
Log.i("ABC", "onSurfaceTextureAvailable(): CameraOrientation(" + cameraId + ")" + info.orientation + " " + previewSize.width + "x" + previewSize.height + " Rotation=" + rotation);
try {
switch (rotation) {
case Surface.ROTATION_0:
mCamera.setDisplayOrientation(90);
mTextureView.setLayoutParams(new FrameLayout.LayoutParams(
previewSize.height, previewSize.width, Gravity.CENTER));
transform.setScale(-1, 1, previewSize.height/2, 0);
break;
case Surface.ROTATION_90:
mCamera.setDisplayOrientation(0);
mTextureView.setLayoutParams(new FrameLayout.LayoutParams(
previewSize.width, previewSize.height, Gravity.CENTER));
transform.setScale(-1, 1, previewSize.width/2, 0);
break;
case Surface.ROTATION_180:
mCamera.setDisplayOrientation(270);
mTextureView.setLayoutParams(new FrameLayout.LayoutParams(
previewSize.height, previewSize.width, Gravity.CENTER));
transform.setScale(-1, 1, previewSize.height/2, 0);
break;
case Surface.ROTATION_270:
mCamera.setDisplayOrientation(180);
mTextureView.setLayoutParams(new FrameLayout.LayoutParams(
previewSize.width, previewSize.height, Gravity.CENTER));
transform.setScale(-1, 1, previewSize.width/2, 0);
break;
}
mCamera.setPreviewTexture(mSurfaceTexture);
Log.i("ABC", "onSurfaceTextureAvailable(): Transform: " + transform.toString());
mCamera.startPreview();
// mTextureView.setVisibility(0);
mCamera.setPreviewCallback(new PreviewCallback() {
@Override
public void onPreviewFrame(byte[] data, Camera camera) {
if (data == null) return;
Camera.Size size = mCamera.getParameters().getPreviewSize();
if (size == null) return;
//This is where I start my thread that analyzes images
DetectionThread thread = new DetectionThread(data, size.width, size.height);
thread.start();
}
});
}
catch (Exception t) {
Log.i("ABC", "onSurfaceTextureAvailable Exception: "+ t.getMessage());
}
}
However, similarly as in the other case, since my analyzing thread starts inside the onSurfaceTextureAvailable, which is only when the texture is there, and not when I open up another application, the frame capturing won't continue when I open up something else.
Some ideas have shown that it's possible, but I just don't know how. There was an idea, that I could implement SurfaceTexture.onFrameAvailable and then once new frame is available, trigger a runnable to be ran on render thread (GLSurfaceView.queueEvent(..)) and finally run a runnable call SurfaceTexture.updateTexImage(). Which is what I've tried (it's commented out in my code), but it doesn't work, the application crashes if I do that.
What else can I possibly do? I know that this can work somehow, because I've seen it used in apps like SpyCameraOS (yes, I know it's open-source and I've looked at the code, but I couldn't make a working solution), and I feel like I'm missing just a small piece somewhere, but I have no idea what I'm doing wrong. I've been at this for the past 3 days, and no success.
Help would be greatly appreciated.
回答1:
Summarizing the comments: direct the output of the Camera to a SurfaceTexture that isn't tied to a View object. A TextureView will be destroyed when the activity is paused, freeing its SurfaceTexture, but if you create a separate SurfaceTexture (or detach the one from the TextureView) then it won't be affected by changes in Activity state. The texture can be rendered to an off-screen Surface, from which pixels can be read.
Various examples can be found in Grafika.
来源：https://stackoverflow.com/questions/28222407/capture-camera-frames-in-background-android