Second ProgramâAVI Video
Playing a video with OpenCV is almost as easy as displaying a single picture. The only new issue we face is that we need some kind of loop to read each frame in sequence; we may also need some way to get out of that loop if the movie is too boring. See Example 2-2.
Example 2-2. A simple OpenCV program for playing a video file from disk
#include "highgui.h" int main( int argc, char** argv ) { cvNamedWindow( "Example2", CV_WINDOW_AUTOSIZE ); CvCapture* capture = cvCreateFileCapture( argv[1] ); IplImage* frame; while(1) { frame = cvQueryFrame( capture ); if( !frame ) break; cvShowImage( "Example2", frame ); char c = cvWaitKey(33); if( c == 27 ) break; } cvReleaseCapture( &capture ); cvDestroyWindow( "Example2" ); }
Here we begin the function main()
with the usual
creation of a named window, in this case "Example2
".
Things get a little more interesting after that.
CvCapture* capture = cvCreateFileCapture( argv[1] );
The function cvCreateFileCapture()
takes as its
argument the name of the AVI file to be loaded and then returns a pointer to a CvCapture
structure. This structure contains all of the
information about the AVI file being read, including state information. When
created in this way, the CvCapture
structure is
initialized to the beginning of the AVI.
frame = cvQueryFrame( capture );
Once inside of the while(1)
loop, we begin reading from the AVI file. cvQueryFrame()
takes as its argument a pointer to a CvCapture
structure. It then grabs the next video ...
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