Opencv does not write video - c++

Question

I am trying to write a very basic video capturing program using opencv, but despite all my efforts, nothing gets written. I am fairly sure that i am following all the tutorials one can find on the subject.
Here is the code i am using:
#include <opencv2\core\core.hpp>
#include <opencv2\imgproc\imgproc.hpp>
#include <opencv2\highgui\highgui.hpp>
#include <videoInput.h>
static const cv::Size _SIZE(640, 480);
static const int FPS = 20;
int webcam = 0;
std::auto_ptr<videoInput> VI(NULL);
std::auto_ptr<cv::VideoWriter> outputVideo(NULL);
cv::Mat frame(_SIZE.height, _SIZE.width, CV_8UC3);
// get device list create videoInput
videoInput::listDevices();
VI.reset(new videoInput())
// choose first device
VI->setupDevice(webcam, _SIZE.width, _SIZE.height);
// always check
if(!VI->isDeviceSetup(webcam))
return -1; //-->
// set device frame rate
VI->setIdealFramerate(webcam, FPS);
// create named window and image
cv::namedWindow("CAM");
do
if (VI->isFrameNew(webcam))
{
VI->getPixels(webcam, (unsigned char*)frame.data, false, true); // получение пикселей в BGR
if (outputVideo.get())
{
(*outputVideo).write( frame);
}
char c = cv::waitKey(5);
if (!IsWindowVisible((HWND)cvGetWindowHandle("CAM")) || c==27)
{
exit(0);
}
cv::imshow("CAM", frame);
} while(1);
I have tried various extension and various Fourcc values. Usually, on any extension except avi, writer is created but does nothing. on the contrary, avi files writers simply fail to be created.
I have read that probably codecs are missing, but what does that mean - what exactly do i need to put where for them to be found by opencv?
All in all, i am very confused. This is tutorial code, it should work.