added static function to set preferred subtype for Directshow capture / Windows (#8433)

* added static function to set preferred subtype for Directshow capture / Windows

* missing implementation

Author: ofTheo

libs/openFrameworks/video/ofDirectShowGrabber.cpp

@@ -1,6 +1,17 @@
 #include "ofDirectShowGrabber.h"
 #include "ofUtils.h"
 #ifdef TARGET_WIN32
+
+//--------------------------------------------------------------------
+//Static members / functions 
+
+int ofDirectShowGrabber::preferredFormat = -1; 
+
+void ofDirectShowGrabber::setPreferredFormat(int aPreferredFormat) {
+	preferredFormat = aPreferredFormat;
+}
+
+
 //--------------------------------------------------------------------
 ofDirectShowGrabber::ofDirectShowGrabber(){
 
@@ -51,6 +62,9 @@ bool ofDirectShowGrabber::setup(int w, int h){
 		height = h;
 		bGrabberInited = false;
 
+		if (preferredFormat >= 0) {
+			VI.setRequestedMediaSubType(preferredFormat);
+		}
 		if( attemptFramerate >= 0){
 			VI.setIdealFramerate(device, attemptFramerate);
 		}

libs/openFrameworks/video/ofDirectShowGrabber.h

@@ -32,6 +32,13 @@ class ofDirectShowGrabber : public ofBaseVideoGrabber{
 		ofDirectShowGrabber();
 		virtual ~ofDirectShowGrabber();
 
+		/// \brief Sets the preffered DirectShow media subtype - MJPG / H264 can provide faster framerates 
+		///
+		/// /use formats like: MEDIASUBTYPE_H264, MEDIASUBTYPE_MJPG, MEDIASUBTYPE_Y800 etc, default is: MEDIASUBTYPE_RGB24
+		/// /use -1 to revert to the default behavior 
+		///
+		static void setPreferredFormat(int aPreferredFormat); 		
+
 		std::vector<ofVideoDevice>	listDevices() const;
 		bool					setup(int w, int h);
 		void					update();
@@ -56,9 +63,6 @@ class ofDirectShowGrabber : public ofBaseVideoGrabber{
 		void					setDeviceID(int _deviceID);
 		void					setDesiredFrameRate(int framerate);
 
-
-		
-
 	protected:
 
 		bool					bChooseDevice;
@@ -70,6 +74,7 @@ class ofDirectShowGrabber : public ofBaseVideoGrabber{
 		bool 					bIsFrameNew;	
 
 		int						width, height;	
+		static int				preferredFormat; 
 		//--------------------------------- directshow
 		#ifdef OF_VIDEO_CAPTURE_DIRECTSHOW
 			int 					device;