video/opencv: fix crash with obscure backends

Issue: #726

3 files changed, 14 insertions, 2 deletions

diff --git a/video-opencv/impl-camera.cpp b/video-opencv/impl-camera.cpp
index 8a540134..3f2a1b1a 100644
--- a/video-opencv/impl-camera.cpp
+++ b/video-opencv/impl-camera.cpp
@@ -33,7 +33,7 @@ bool cam::is_open()
 bool cam::start(info& args)
 {
     stop();
-    cap.emplace(idx);
+    cap.emplace(idx + video_capture_backend);
 
     if (args.width > 0 && args.height > 0)
     {
diff --git a/video-opencv/impl.hpp b/video-opencv/impl.hpp
index 3d793490..db569823 100644
--- a/video-opencv/impl.hpp
+++ b/video-opencv/impl.hpp
@@ -31,6 +31,15 @@ struct metadata : camera_
 
 struct cam final : camera
 {
+static constexpr int video_capture_backend =
+#ifdef _WIN32
+    cv::CAP_DSHOW;
+#elif !defined __APPLE__
+    cv::CAP_V4L2;
+#else
+    cv::CAP_ANY;
+#endif
+
     cam(int idx);
     ~cam() override;
 
diff --git a/video-opencv/video-property-page.cpp b/video-opencv/video-property-page.cpp
index a43a5ba0..078898a5 100644
--- a/video-opencv/video-property-page.cpp
+++ b/video-opencv/video-property-page.cpp
@@ -14,6 +14,7 @@
 #include "compat/run-in-thread.hpp"
 #include "compat/library-path.hpp"
 #include "compat/thread-name.hpp"
+#include "impl.hpp"
 
 #include <cstring>
 
@@ -49,6 +50,7 @@ prop_settings_worker::prop_settings_worker(int idx_)
     int ret = (int)cap.get(cv::CAP_PROP_SETTINGS);
 
     if (ret != 0)
+    {
         run_in_thread_async(qApp, [] {
             QMessageBox::warning(nullptr,
                                  "Camera properties",
@@ -56,6 +58,7 @@ prop_settings_worker::prop_settings_worker(int idx_)
                                  QMessageBox::Cancel,
                                  QMessageBox::NoButton);
         });
+    }
     else
     {
         idx = idx_;
@@ -67,7 +70,7 @@ prop_settings_worker::prop_settings_worker(int idx_)
 
 void prop_settings_worker::open_prop_page()
 {
-    cap.open(idx);
+    cap.open(idx + opencv_camera_impl::cam::video_capture_backend);
 
     if (cap.isOpened())
     {