From f59a955bea1df94218d698a4a8b1d3507fd9153c Mon Sep 17 00:00:00 2001
From: Alexander Smorkalov <alexander.smorkalov@opencv.ai>
Date: Tue, 15 Jul 2025 13:25:40 +0300
Subject: [PATCH] Added command line option to select VideoCapture backend.

---
 apps/interactive-calibration/calibCommon.hpp  |  1 +
 .../interactive-calibration/calibPipeline.cpp |  4 +--
 apps/interactive-calibration/main.cpp         | 26 ++++++++++++++++---
 .../parametersController.cpp                  | 23 +++++++++++++++-
 4 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/apps/interactive-calibration/calibCommon.hpp b/apps/interactive-calibration/calibCommon.hpp
index 73cb4ab9fc..ed6c3613d1 100644
--- a/apps/interactive-calibration/calibCommon.hpp
+++ b/apps/interactive-calibration/calibCommon.hpp
@@ -92,6 +92,7 @@ namespace calib
         std::string videoFileName;
         bool flipVertical;
         int camID;
+        int camBackend;
         int fps;
         cv::Size cameraResolution;
         int maxFramesNum;
diff --git a/apps/interactive-calibration/calibPipeline.cpp b/apps/interactive-calibration/calibPipeline.cpp
index ac54764e41..4eae5469d6 100644
--- a/apps/interactive-calibration/calibPipeline.cpp
+++ b/apps/interactive-calibration/calibPipeline.cpp
@@ -34,7 +34,7 @@ PipelineExitStatus CalibPipeline::start(std::vector<cv::Ptr<FrameProcessor> > pr
     auto open_camera = [this] () {
         if(mCaptureParams.source == Camera)
         {
-            mCapture.open(mCaptureParams.camID);
+            mCapture.open(mCaptureParams.camID, mCaptureParams.camBackend);
             cv::Size maxRes = getCameraResolution();
             cv::Size neededRes = mCaptureParams.cameraResolution;
 
@@ -55,7 +55,7 @@ PipelineExitStatus CalibPipeline::start(std::vector<cv::Ptr<FrameProcessor> > pr
             mCapture.set(cv::CAP_PROP_AUTOFOCUS, 0);
         }
         else if (mCaptureParams.source == File)
-            mCapture.open(mCaptureParams.videoFileName);
+            mCapture.open(mCaptureParams.videoFileName, mCaptureParams.camBackend);
     };
 
     if(!mCapture.isOpened()) {
diff --git a/apps/interactive-calibration/main.cpp b/apps/interactive-calibration/main.cpp
index 92ea2a93ae..b9ec7e8805 100644
--- a/apps/interactive-calibration/main.cpp
+++ b/apps/interactive-calibration/main.cpp
@@ -6,7 +6,7 @@
 #include <opencv2/calib3d.hpp>
 #include <opencv2/cvconfig.h>
 #include <opencv2/highgui.hpp>
-
+#include <opencv2/videoio/registry.hpp>
 
 #include <string>
 #include <vector>
@@ -23,9 +23,25 @@
 
 using namespace calib;
 
-const std::string keys  =
+static std::string getVideoIoBackendsString()
+{
+    std::string result;
+    auto backs = cv::videoio_registry::getBackends();
+    for (const auto& b: backs)
+    {
+        if (!result.empty())
+            result += ", ";
+
+        result += cv::videoio_registry::getBackendName(b);
+    }
+
+    return result;
+}
+
+const char* keys  =
         "{v        |         | Input from video file }"
-        "{ci       | 0       | Default camera id }"
+        "{ci       | 0       | Camera id }"
+        "{vb       |         | Video I/O back-end. One of: %s }"
         "{flip     | false   | Vertical flip of input frames }"
         "{t        | circles | Template for calibration (circles, chessboard, dualCircles, charuco, symcircles) }"
         "{sz       | 16.3    | Distance between two nearest centers of circles or squares on calibration board}"
@@ -95,11 +111,13 @@ static void undistortButton(int state, void* data)
 
 int main(int argc, char** argv)
 {
-    cv::CommandLineParser parser(argc, argv, keys);
+    cv::CommandLineParser parser(argc, argv, cv::format(keys, getVideoIoBackendsString().c_str()));
+
     if(parser.has("help")) {
         parser.printMessage();
         return 0;
     }
+
     std::cout << consoleHelp << std::endl;
     parametersController paramsController;
 
diff --git a/apps/interactive-calibration/parametersController.cpp b/apps/interactive-calibration/parametersController.cpp
index 4ce81f352a..90d24b04c9 100644
--- a/apps/interactive-calibration/parametersController.cpp
+++ b/apps/interactive-calibration/parametersController.cpp
@@ -4,7 +4,7 @@
 
 #include "parametersController.hpp"
 #include <opencv2/objdetect/aruco_dictionary.hpp>
-
+#include <opencv2/videoio/registry.hpp>
 #include <iostream>
 
 template <typename T>
@@ -106,6 +106,27 @@ bool calib::parametersController::loadFromParser(cv::CommandLineParser &parser)
         mCapParams.camID = parser.get<int>("ci");
     }
 
+    mCapParams.camBackend = cv::CAP_ANY;
+    if (parser.has("vb"))
+    {
+        std::string backendName = parser.get<std::string>("vb");
+        auto backs = cv::videoio_registry::getBackends();
+        bool backendSet = false;
+        for (const auto& b: backs)
+        {
+            if (backendName == cv::videoio_registry::getBackendName(b))
+            {
+                mCapParams.camBackend = b;
+                backendSet = true;
+            }
+        }
+        if (!backendSet)
+        {
+            std::cout << "Unknown or unsupported backend " << backendName << std::endl;
+            return false;
+        }
+    }
+
     std::string templateType = parser.get<std::string>("t");
 
     if(templateType.find("symcircles", 0) == 0) {