Preview callback

[liberorignanese]

it would be helpful if there was a callback for reading preview frame.

[Carpetfizz]

Any update on this? Is there no way to read frame data from the camera?

[xCatG]

Hi All,
I'm trying to add support for accessing preview frames, my current thinking is in CameraViewImpl, add a interface like

interface FrameCallback {
    void onFrame(byte[] data, int format);
}

We can then add a mFrameCallback so each subclasses can deal with it. In Camera1, in openCamera we can call setPreviewCallback to supply us with the frame; in Camera2 we add an extra ImageReader that does the per-frame reading, and on its callback we can again call onFrame() with the byte from the Image object, as well as its format.

int format in the onFrame() call might be changed to a different object containing image info, not sure yet as I haven't start coding.

Where I am not sure is how to accept a external hook from CameraView itself. I am not sure how many people will want this behavior by default, so a separate CameraViewWithPreviewCall that extends CameraView might be more desirable? Also, given these are usually inflated from layout xml, the entry where we set callbacks might not be easy (to be seen, again, I haven't start coding yet).

Any thoughts, comments?

[xCatG]

Another approach is
Add void onFrame(byte[] data, int format);' to CameraView.Callback, as well as CameraViewImpl.Callback. In Camera1, we call this in the onPreviewFrame(); in Camera2, this is called on a ImageReader's OnImageAvailableListener`.

@yaraki out of the two approaches, which one you prefer? Or you have other approaches that I should explore more about?

[xCatG]

The reason for including format as part of the callback is because Camera1 uses ImageFormat.NV21 or ImageFormat.YV12 and Camera2 recommends ImageFormat.YUV_420_888.

Haven't dig more, but we might have to also include image width and height, event stride value to correctly decode things. Still trying things out right now.

[xCatG]

PR #123 by @Sumsar is basically the second approach.

[jackyhieu1211]

@xCatG
Camera1 on device HTC Butterfly 4.3 API 18 not call
mCamera.setPreviewCallback(new Camera.PreviewCallback() {
@OverRide
public void onPreviewFrame(byte[] data, Camera camera) {
Timber.e("onPreviewFrame");
final Camera.Parameters parameters = camera.getParameters();
final int width = parameters.getPreviewSize().width;
final int height = parameters.getPreviewSize().height;
mCallback.onPreviewFrame(data, parameters.getPreviewFormat(), width, height);
}
});