video: add one more constructor for VideoWriter

modules/videoio/include/opencv2/videoio.hpp

@@ -114,7 +114,8 @@ enum VideoCaptureAPIs {
        CAP_GSTREAMER    = 1800,         //!< GStreamer
        CAP_FFMPEG       = 1900,         //!< Open and record video file or stream using the FFMPEG library
        CAP_IMAGES       = 2000,         //!< OpenCV Image Sequence (e.g. img_%02d.jpg)
-       CAP_ARAVIS       = 2100          //!< Aravis SDK
+       CAP_ARAVIS       = 2100,         //!< Aravis SDK
+       CAP_OCV_MJPEG     = 2200         //!< Built-in MotionJPEG codec
      };
 
 /** @brief %VideoCapture generic properties identifier.
@@ -849,6 +850,13 @@ public:
     CV_WRAP VideoWriter(const String& filename, int fourcc, double fps,
                 Size frameSize, bool isColor = true);
 
+    /** @overload
+    The `apiPreference` parameter allows to specify API backends to use. Can be used to enforce a specific reader implementation
+    if multiple are available: e.g. cv::CAP_FFMPEG or cv::CAP_GSTREAMER.
+     */
+    CV_WRAP VideoWriter(int apiPreference, const String& filename, int fourcc, double fps,
+                Size frameSize, bool isColor = true);
+
     /** @brief Default destructor
 
     The method first calls VideoWriter::release to close the already opened file.
@@ -866,6 +874,17 @@ public:
     CV_WRAP virtual bool open(const String& filename, int fourcc, double fps,
                       Size frameSize, bool isColor = true);
 
+    /** @brief Initializes or reinitializes video writer.
+
+    The method opens video writer. Parameters are the same as in the constructor
+    VideoWriter::VideoWriter.
+    @return `true` if video writer has been successfully initialized
+
+    The method first calls VideoWriter::release to close the already opened file.
+     */
+    CV_WRAP bool open(int apiPreference, const String& filename, int fourcc, double fps,
+                      Size frameSize, bool isColor = true);
+
     /** @brief Returns true if video writer has been successfully initialized.
     */
     CV_WRAP virtual bool isOpened() const;

modules/videoio/include/opencv2/videoio/videoio_c.h

@@ -124,7 +124,8 @@ enum
     CV_CAP_FFMPEG = 1900,    // FFMPEG
     CV_CAP_IMAGES = 2000,    // OpenCV Image Sequence (e.g. img_%02d.jpg)
 
-    CV_CAP_ARAVIS = 2100     // Aravis GigE SDK
+    CV_CAP_ARAVIS = 2100,     // Aravis GigE SDK
+    CV_CAP_OCV_MJPEG = 2200   // Built-in MotionJPEG codec
 };
 
 /** @brief start capturing frames from camera: index = camera_index + domain_offset (CV_CAP_*)

modules/videoio/src/cap.cpp

@@ -371,47 +371,59 @@ CV_IMPL CvCapture * cvCreateFileCapture (const char * filename)
 CV_IMPL CvVideoWriter* cvCreateVideoWriter( const char* filename, int fourcc,
                                             double fps, CvSize frameSize, int is_color )
 {
-    // If none of the writers is used
-    // these statements suppress 'unused parameter' warnings.
+    return cvCreateVideoWriterWithPreference(CV_CAP_ANY, filename, fourcc, fps, frameSize, is_color);
+}
+
+CvVideoWriter* cvCreateVideoWriterWithPreference(int apiPreference, const char* filename, int fourcc,
+                                            double fps, CvSize frameSize, int is_color )
+{
     CV_UNUSED(frameSize);
     CV_UNUSED(is_color);
 
-    //CV_FUNCNAME( "cvCreateVideoWriter" );
-
     CvVideoWriter *result = 0;
 
     if(!fourcc || !fps)
         TRY_OPEN(result, cvCreateVideoWriter_Images(filename))
 
-#ifdef HAVE_FFMPEG
+    switch(apiPreference)
+    {
+        default:
+            //exit if the specified API is unavaliable
+            if (apiPreference != CV_CAP_ANY) break;
+        #ifdef HAVE_FFMPEG
+        case CV_CAP_FFMPEG:
             TRY_OPEN(result, cvCreateVideoWriter_FFMPEG_proxy (filename, fourcc, fps, frameSize, is_color))
-#endif
-
-#ifdef HAVE_VFW
+            if (apiPreference != CV_CAP_ANY) break;
+        #endif
+        #ifdef HAVE_VFW
+        case CV_CAP_VFW:
             TRY_OPEN(result, cvCreateVideoWriter_VFW(filename, fourcc, fps, frameSize, is_color))
-#endif
-
-#ifdef HAVE_MSMF
+            if (apiPreference != CV_CAP_ANY) break;
+        #endif
+        #ifdef HAVE_MSMF
+        case CV_CAP_MSMF:
             TRY_OPEN(result, cvCreateVideoWriter_MSMF(filename, fourcc, fps, frameSize, is_color))
-#endif
-
-/*  #ifdef HAVE_XINE
-    TRY_OPEN(result, cvCreateVideoWriter_XINE(filename, fourcc, fps, frameSize, is_color))
+            if (apiPreference != CV_CAP_ANY) break;
         #endif
-*/
-#ifdef HAVE_AVFOUNDATION
+        #ifdef HAVE_AVFOUNDATION
+        case CV_CAP_AVFOUNDATION:
             TRY_OPEN(result, cvCreateVideoWriter_AVFoundation(filename, fourcc, fps, frameSize, is_color))
-#endif
-
-#if defined(HAVE_QUICKTIME) || defined(HAVE_QTKIT)
+            if (apiPreference != CV_CAP_ANY) break;
+        #endif
+        #if defined(HAVE_QUICKTIME) || defined(HAVE_QTKIT)
+        case(CV_CAP_QT):
             TRY_OPEN(result, cvCreateVideoWriter_QT(filename, fourcc, fps, frameSize, is_color))
-#endif
-
-#ifdef HAVE_GSTREAMER
-    TRY_OPEN(result, cvCreateVideoWriter_GStreamer(filename, fourcc, fps, frameSize, is_color))
-#endif
-
+            if (apiPreference != CV_CAP_ANY) break;
+        #endif
+        #ifdef HAVE_GSTREAMER
+        case CV_CAP_GSTREAMER:
+            TRY_OPEN(result, cvCreateVideoWriter_GStreamer (filename, fourcc, fps, frameSize, is_color))
+            if (apiPreference != CV_CAP_ANY) break;
+        #endif
+        case CV_CAP_IMAGES:
             TRY_OPEN(result, cvCreateVideoWriter_Images(filename))
+            if (apiPreference != CV_CAP_ANY) break;
+    }
 
     return result;
 }
@@ -543,10 +555,11 @@ static Ptr<IVideoCapture> IVideoCapture_create(const String& filename)
     return Ptr<IVideoCapture>();
 }
 
-static Ptr<IVideoWriter> IVideoWriter_create(const String& filename, int _fourcc, double fps, Size frameSize, bool isColor)
+static Ptr<IVideoWriter> IVideoWriter_create(int apiPreference, const String& filename, int _fourcc, double fps, Size frameSize, bool isColor)
 {
     Ptr<IVideoWriter> iwriter;
-    if( _fourcc == CV_FOURCC('M', 'J', 'P', 'G') )
+    if( (apiPreference == CAP_OCV_MJPEG || apiPreference == CAP_ANY)
+            && _fourcc == CV_FOURCC('M', 'J', 'P', 'G') )
         iwriter = createMotionJpegWriter(filename, fps, frameSize, isColor);
     return iwriter;
 }
@@ -725,6 +738,12 @@ VideoWriter::VideoWriter(const String& filename, int _fourcc, double fps, Size f
     open(filename, _fourcc, fps, frameSize, isColor);
 }
 
+
+VideoWriter::VideoWriter(int apiPreference, const String& filename, int _fourcc, double fps, Size frameSize, bool isColor)
+{
+    open(apiPreference, filename, _fourcc, fps, frameSize, isColor);
+}
+
 void VideoWriter::release()
 {
     iwriter.release();
@@ -737,14 +756,19 @@ VideoWriter::~VideoWriter()
 }
 
 bool VideoWriter::open(const String& filename, int _fourcc, double fps, Size frameSize, bool isColor)
+{
+    return open(CAP_ANY, filename, _fourcc, fps, frameSize, isColor);
+}
+
+bool VideoWriter::open(int apiPreference, const String& filename, int _fourcc, double fps, Size frameSize, bool isColor)
 {
     CV_INSTRUMENT_REGION()
 
     if (isOpened()) release();
-    iwriter = IVideoWriter_create(filename, _fourcc, fps, frameSize, isColor);
+    iwriter = IVideoWriter_create(apiPreference, filename, _fourcc, fps, frameSize, isColor);
     if (!iwriter.empty())
         return true;
-    writer.reset(cvCreateVideoWriter(filename.c_str(), _fourcc, fps, frameSize, isColor));
+    writer.reset(cvCreateVideoWriterWithPreference(apiPreference, filename.c_str(), _fourcc, fps, frameSize, isColor));
     return isOpened();
 }
 

modules/videoio/src/precomp.hpp

@@ -163,6 +163,10 @@ CvCapture * cvCreateCameraCapture_Unicap  (const int     index);
 CvCapture * cvCreateCameraCapture_PvAPI  (const int     index);
 CvVideoWriter* cvCreateVideoWriter_GStreamer( const char* filename, int fourcc,
                                             double fps, CvSize frameSize, int is_color );
+CvVideoWriter* cvCreateVideoWriterWithPreference(int api, const char* filename, int fourcc,
+                                           double fps, CvSize frame_size,
+                                           int is_color CV_DEFAULT(1));
+
 
 namespace cv
 {