Repository: opencv
Issue: OpenCV Crashes when reopening camera on Mac OSX Sierra and displaying
Labels: bug,priority: low,category: videoio(camera),platform: ios/osx

Reposting from [SO](http://stackoverflow.com/questions/40443825/opencv-crashes-when-reopening-camera-on-mac-osx-sierra-and-displaying):
When I reopen a webcam in OpenCV on Mac OSX Sierra, and I display images from it, I get NSExceptions.

This is the test code I'm working with to try to figure out the error mode.
```
import cv2

cam = cv2.VideoCapture(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)

cam.open(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)

cam.open(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)

cam.open(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)
```
The error I'm getting is:
```
2016-11-05 18:15:07.075 Python[1082:24157] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'An instance 0x7fca4ac3a6f0 of class AVCaptureDALDevice was deallocated while key value observers were still registered with it. Current observation info: <NSKeyValueObservationInfo 0x7fca4ac42f80> (
<NSKeyValueObservance 0x7fca4ae6df50: Observer: 0x7fca4ae6b410, Key path: open, Options: <New: NO, Old: NO, Prior: NO> Context: 0x7fffc9c99570, Property: 0x7fca4ac3fe30>
)'
*** First throw call stack:
(
    0   CoreFoundation                      0x00007fffafde96fb __exceptionPreprocess + 171
    1   libobjc.A.dylib                     0x00007fffc45f0a2a objc_exception_throw + 48
    2   CoreFoundation                      0x00007fffafe669a5 +[NSException raise:format:] + 197
    3   Foundation                          0x00007fffb17d1d84 NSKVODeallocate + 293
    4   AVFoundation                        0x00007fffac67dabe -[AVCaptureDeviceInput _setDevice:exceptionReason:] + 304
    5   AVFoundation                        0x00007fffac5ae914 -[AVCaptureDeviceInput dealloc] + 39
    6   CoreFoundation                      0x00007fffafe53a7b -[__NSSingleObjectArrayI dealloc] + 43
    7   libobjc.A.dylib                     0x00007fffc45e5e60 _ZN12_GLOBAL__N_119AutoreleasePoolPage3popEPv + 808
    8   CoreFoundation                      0x00007fffafd20d66 _CFAutoreleasePoolPop + 22
    9   CoreFoundation                      0x00007fffafd612c5 __CFRunLoopRun + 2229
    10  CoreFoundation                      0x00007fffafd607b4 CFRunLoopRunSpecific + 420
    11  HIToolbox                           0x00007fffaf2fcfbc RunCurrentEventLoopInMode + 240
    12  HIToolbox                           0x00007fffaf2fcdf1 ReceiveNextEventCommon + 432
    13  HIToolbox                           0x00007fffaf2fcc26 _BlockUntilNextEventMatchingListInModeWithFilter + 71
    14  AppKit                              0x00007fffad9e6b79 _DPSNextEvent + 1093
    15  AppKit                              0x00007fffae0fc1c3 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1637
    16  libopencv_highgui.2.4.dylib         0x000000010d79c0a6 cvWaitKey + 402
    17  cv2.so                              0x000000010cfa3ce1 _ZL16pyopencv_waitKeyP7_objectS0_S0_ + 103
    18  Python                              0x000000010cc001ab PyEval_EvalFrameEx + 27003
    19  Python                              0x000000010cbf963a PyEval_EvalCodeEx + 1617
    20  Python                              0x000000010cbf8fe3 PyEval_EvalCode + 48
    21  Python                              0x000000010cc1cc04 run_mod + 53
    22  Python                              0x000000010cc1cca7 PyRun_FileExFlags + 133
    23  Python                              0x000000010cc1c7f8 PyRun_SimpleFileExFlags + 702
    24  Python                              0x000000010cc2deba Py_Main + 3094
    25  libdyld.dylib                       0x00007fffc4ecd255 start + 1
    26  ???                                 0x0000000000000002 0x0 + 2
)
libc++abi.dylib: terminating with uncaught exception of type NSException
Abort trap: 6
```
I get this error consistently when I run it from iTerm or terminal. But I get it inconsistently from xterm.

I also get the same error when using cam.release() prior to all calls to cam.open(0).
```
import cv2

cam = cv2.VideoCapture(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)
cam.release()

cam.open(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)
cam.release()

cam.open(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)
cam.release()

cam.open(0)
ret, im = cam.read()
cv2.imshow('im', im)
cv2.waitKey(1)
cam.release()
```