Called by the service when it needs the latest video frame. The frame should be provided through a call to the ITextCaptureService.submitRequestedFrame method.
This method is to be implemented on the client side.
void onRequestLatestFrame( byte buffer )
The buffer to be filled with image data for latest frame. Only NV21 format is currently supported.
Can be passed directly to Camera.addCallbackBuffer. When the buffer is filled with data, it should be passed back to the service by calling submitRequestedFrame.