Added the How to create videos with OpenCV Tutorial. Made some corrections to the feature2d, to get rid of some documentation build errors.

samples/cpp/tutorial_code/HighGUI/video-write/video-write.cpp

@@ -0,0 +1,97 @@
+#include <iostream>	// for standard I/O
+#include <string>   // for strings
+
+#include <opencv2/core/core.hpp>        // Basic OpenCV structures (cv::Mat)
+#include <opencv2/highgui/highgui.hpp>  // Video write
+
+using namespace std;
+using namespace cv;
+
+void help()
+{
+    cout
+        << "\n--------------------------------------------------------------------------" << endl
+        << "This program shows how to write video files. You can extract the R or G or B color channel "
+        << " of the input video.write "  << endl
+        << "Usage:"                                                               << endl
+        << "./video-write inputvideoName [ R | G | B] [Y | N]"                   << endl
+        << "--------------------------------------------------------------------------"   << endl
+        << endl;
+}
+int main(int argc, char *argv[], char *window_name)
+{
+    help();
+    if (argc != 4)
+    {
+        cout << "Not enough parameters" << endl;
+        return -1;
+    }
+
+    const string source      = argv[1];            // the source file name
+    const bool askOutputType = argv[3][0] =='Y';  // If false it will use the inputs codec type
+   
+    VideoCapture inputVideo(source);        // Open input
+    if ( !inputVideo.isOpened())
+    {
+        cout  << "Could not open the input video." << source << endl;
+        return -1;
+    }
+
+    string::size_type pAt = source.find_last_of('.');   // Find extension point
+    const string NAME = source.substr(0, pAt) + argv[2][0] + ".avi";   // Form the new name with container
+    int ex = static_cast<int>(inputVideo.get(CV_CAP_PROP_FOURCC));     // Get Codec Type- Int form
+
+    // Transform from int to char via Bitwise operators
+    char EXT[] = {ex & 0XFF , (ex & 0XFF00) >> 8,(ex & 0XFF0000) >> 16,(ex & 0XFF000000) >> 24, 0};
+
+    Size S = Size((int) inputVideo.get(CV_CAP_PROP_FRAME_WIDTH),    //Acquire input size
+                  (int) inputVideo.get(CV_CAP_PROP_FRAME_HEIGHT));    
+
+    VideoWriter outputVideo;                                        // Open the output
+    if (askOutputType)
+            outputVideo.open(NAME  , ex=-1, inputVideo.get(CV_CAP_PROP_FPS),S, true);  
+    else
+        outputVideo.open(NAME , ex, inputVideo.get(CV_CAP_PROP_FPS),S, true);
+    
+    if (!outputVideo.isOpened())
+    {
+        cout  << "Could not open the output video for write: " << source << endl;
+        return -1;
+    }
+
+    union { int v; char c[5];} uEx ;
+    uEx.v = ex;                              // From Int to char via union
+    uEx.c[4]='\0';
+
+    cout << "Input frame resolution: Width=" << S.width << "  Height=" << S.height
+        << " of nr#: " << inputVideo.get(CV_CAP_PROP_FRAME_COUNT) << endl;
+    cout << "Input codec type: " << EXT << endl;
+
+    int channel = 2;    // Select the channel to save
+    switch(argv[2][0])
+    {
+    case 'R' : {channel = 2; break;}
+    case 'G' : {channel = 1; break;}
+    case 'B' : {channel = 0; break;}
+    }
+    Mat src,res;
+    vector<Mat> spl; 
+
+    while( true) //Show the image captured in the window and repeat
+    {
+        inputVideo >> src;              // read
+        if( src.empty()) break;         // check if at end
+
+       split(src, spl);                 // process - extract only the correct channel
+       for( int i =0; i < 3; ++i)       
+        if (i != channel)
+           spl[i] = Mat::zeros(S, spl[0].type());
+       merge(spl, res);
+
+       //outputVideo.write(res); //save or
+       outputVideo << res;
+    }
+
+    cout << "Finished writing" << endl;
+    return 0;
+}