Added framerate decimation

Former-commit-id: 8f7eb09978aef5364cbab1f5dfe12afbf60e6cac

test/v4l2png/V4L2Grabber.cpp

@@ -19,13 +19,16 @@
 
 #define CLEAR(x) memset(&(x), 0, sizeof(x))
 
-V4L2Grabber::V4L2Grabber(const std::string &device, int input, VideoStandard videoStandard, double fps) :
+V4L2Grabber::V4L2Grabber(const std::string &device, int input, VideoStandard videoStandard, int frameDecimation, int pixelDecimation) :
 	_deviceName(device),
 	_ioMethod(IO_METHOD_MMAP),
 	_fileDescriptor(-1),
 	_buffers(),
 	_width(0),
-    _height(0)
+	_height(0),
+	_frameDecimation(frameDecimation),
+	_pixelDecimation(pixelDecimation),
+	_currentFrame(0)
 {
 	open_device();
 	init_device(videoStandard, input);
@@ -42,23 +45,24 @@ void V4L2Grabber::start()
 	start_capturing();
 }
 
-void V4L2Grabber::capture()
+void V4L2Grabber::capture(int frameCount)
 {
-    int count = 1;
-    while (count-- > 0) {
-            for (;;) {
+	for (int count = 0; count < frameCount || frameCount < 0; ++count)
+	{
+		for (;;)
+		{
+			// the set of file descriptors for select
 			fd_set fds;
-                    struct timeval tv;
-                    int r;
-
 			FD_ZERO(&fds);
 			FD_SET(_fileDescriptor, &fds);
 
-                    /* Timeout. */
+			// timeout
+			struct timeval tv;
 			tv.tv_sec = 2;
 			tv.tv_usec = 0;
 
-                    r = select(_fileDescriptor + 1, &fds, NULL, NULL, &tv);
+			// block until data is available
+			int r = select(_fileDescriptor + 1, &fds, NULL, NULL, &tv);
 
 			if (-1 == r)
 			{
@@ -545,6 +549,10 @@ int V4L2Grabber::read_frame()
 
 void V4L2Grabber::process_image(const void *p, int size)
 {
+	if (++_currentFrame >= _frameDecimation)
+	{
+		// We do want a new frame...
+
 		if (size != 2*_width*_height)
 		{
 			std::cout << "Frame too small: " << size << " != " << (2*_width*_height) << std::endl;
@@ -552,6 +560,8 @@ void V4L2Grabber::process_image(const void *p, int size)
 		else
 		{
 			process_image(reinterpret_cast<const uint8_t *>(p));
+			_currentFrame = 0; // restart counting
+		}
 	}
 }
 

test/v4l2png/V4L2Grabber.h

@@ -15,12 +15,12 @@ public:
 	};
 
 public:
-    V4L2Grabber(const std::string & device, int input, VideoStandard videoStandard, double fps);
+	V4L2Grabber(const std::string & device, int input, VideoStandard videoStandard, int frameDecimation, int pixelDecimation);
 	virtual ~V4L2Grabber();
 
 	void start();
 
-    void capture();
+	void capture(int frameCount = -1);
 
 	void stop();
 
@@ -73,4 +73,8 @@ private:
 
 	int _width;
 	int _height;
+	const int _frameDecimation;
+	const int _pixelDecimation;
+
+	int _currentFrame;
 };

test/v4l2png/v4l2png.cpp

@@ -40,9 +40,9 @@ int main(int argc, char** argv)
 		return 1;
 	}
 
-    V4L2Grabber grabber("/dev/video0", 0, V4L2Grabber::PAL, 10.0);
+	V4L2Grabber grabber("/dev/video0", 0, V4L2Grabber::PAL, 25, 8);
 	grabber.start();
-    grabber.capture();
+	grabber.capture(250);
 	grabber.stop();
 
 	return 0;