onPreviewFrame not being called for every frame that is displayed on SurfaceView

问题

My subclass of SurfaceView implements Camera.PreviewCallback & SurfaceHolder.Callback.

private SurfaceHolder mHolder;
private Camera mCamera;

private final FPSCounter fpscounter = new FPSCounter();

public MySurfaceView(Context context, AttributeSet attrs) {
    super(context, attrs);
    mHolder = getHolder();
    mHolder.addCallback(this);
}

@Override
public void onPreviewFrame(byte[] data, Camera camera) {
    fpscounter.logFrame();
    Log.d("fps", String.valueOf(fpscounter.getLastFrameCount()));
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    synchronized (this) {
        mCamera.stopPreview();

        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setRecordingHint(true);
        parameters.setPreviewFormat(ImageFormat.NV21);

        mCamera.setParameters(parameters);

        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.setPreviewCallback(this);
            mCamera.startPreview();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    synchronized (this) {
        setWillNotDraw(false);
        mCamera = Camera.open();
    }
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    synchronized (this) {
        try {
            if (mCamera != null) {
                mCamera.stopPreview();
                mCamera.release();
            }
        } catch (Exception e) {
            Log.e("cam error", e.getMessage());
        }
    }
}

and the FPSCounter class

private long startTime; 
private int frames, lastFrameCount;

public void logFrame() {
    frames++;
    if (System.nanoTime() - startTime >= 1000000000) {
        lastFrameCount = frames;
        frames = 0;
        startTime = System.nanoTime();
    }
}

public int getLastFrameCount() {
    return lastFrameCount;
}

Even though the camera preview is extremely smooth, the onPreviewFrame() method is only called about 5 times a second. Why isn't it being called for every frame?

回答1:

You probably figured it out already: Camera.setPreviewCallback() puts too much pressure on Garbage Collector. You can use Camera.setPreviewCallbackWithBuffer() instead.

Second, if onPreviewFrame() arrives on the main (UI) thread, then it competes for single CPU time with UI events like touch, layout, or even rendering. To keep onPreviewFrame() on a separate thread, you should open() the camera on a secondary Looper thread, see e.g. https://stackoverflow.com/a/19154438/192373.

Third, even in this case, the preview callbacks are serialized. If fpscounter.logFrame() and Log().d take X milliseconds, then the FPS will not exceed 1000/X.

回答2:

It is called for every frame. You can refer to online reference of Camera. Look at this sentence "Installs a callback to be invoked for every preview frame in addition to displaying them on the screen."

来源：https://stackoverflow.com/questions/18859260/onpreviewframe-not-being-called-for-every-frame-that-is-displayed-on-surfaceview

标签

android

android-camera

surfaceview