Merge pull request #21337 from mansourmoufid:videocapture-get-property-return

Make cv::VideoCapture::get return cv::CAP_PROP_UNKNOWN (-1) for unsupported properties #21337

The return value indicating an unsupported property is not consistent across backends.

I stumbled on this issue because my code was determining if a property value is valid if it's non-zero (like the documentation says), which worked fine on macOS, but not on Android.

For example, auto-exposure is not supported on macOS, so get() returns 0. But it is supported on Android and 0 means auto-exposure is off.

I think -1 is the better return value to indicate unsupported properties.

I made changes to all the backends. I think I got every case. This breaks API compatibility for some backends, so I based this on branch 3.4.

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
- [x] The PR is proposed to proper branch
- [ ] There is reference to original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/videoio/misc/python/test/test_videoio.py

@@ -45,6 +45,7 @@ class Bindings(NewOpenCVTests):
         with open(self.find_file("cv/video/768x576.avi"), "rb") as f:
             cap = cv.VideoCapture(f, api_pref, [])
             self.assertTrue(cap.isOpened())
+            self.assertEqual(cv.CAP_PROP_UNKNOWN, cap.get(-1))
             hasFrame, frame = cap.read()
             self.assertTrue(hasFrame)
             self.assertEqual(frame.shape, (576, 768, 3))