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/test/test_gstreamer.cpp

@@ -26,6 +26,8 @@ TEST_P(videoio_gstreamer, read_check)
     ASSERT_NO_THROW(cap.open(pipeline.str(), CAP_GSTREAMER));
     ASSERT_TRUE(cap.isOpened());
 
+    EXPECT_EQ(CAP_PROP_UNKNOWN, cap.get(CV__CAP_PROP_LATEST));
+
     Mat buffer, decode_frame, gray_frame, rgb_frame;
     for (int i = 0; i < count_frames; ++i)
     {