OpenCV / cannot open an AVI file

Question

I'm using opencv to detect blinks. I was able to get my project running with a stream captured from camera and everything was fine. I was trying to test my algorithm on a database of *.avi files, but I can't open any of these. I checked the codec version of these and downloaded proper codecs, yet it's still not working. I decided to try to at least try to load the clip, using this code I found somewhere in the internet:

 int main( int argc, char** argv ){
 int key = 0;  

// Initialize camera and OpenCV image  
//CvCapture* capture = cvCaptureFromCAM( 0 );  
CvCapture* capture = cvCaptureFromAVI( "file.avi" );    
IplImage* frame = cvQueryFrame( capture );  

// Check   
if ( !capture )   
{  
    fprintf( stderr, "Cannot open AVI!\n" );  
    return 1;  
}  

// Get the fps, needed to set the delay  
int fps = ( int )cvGetCaptureProperty( capture, CV_CAP_PROP_FPS );  

// Create a window to display the video  
cvNamedWindow( "video", CV_WINDOW_AUTOSIZE );  

while( key != 'x' )   
{  
    // get the image frame   
    frame = cvQueryFrame( capture );  

    // exit if unsuccessful  
    if( !frame ) break;  

    // display current frame   
    cvShowImage( "video", frame );  

    // exit if user presses 'x'          
    key = cvWaitKey( 1000 / fps );  
}  

// Tidy up  
cvDestroyWindow( "video" );  
cvReleaseCapture( &capture );  

return 0; 

}

yet it still doesn't change anything and the capture is still a NULL. Any ideas what I could do now? Thanks in advance!

E: I use opencv 2.4.6 on x64 windows

Answer 1

The code seems to be correct.

You tagged the question as C++, but IplImage is derived from Intel Image Processing library and is part of native OpenCV C library. in OpenCV C++ library i guess there is no IplImage (or is not supposed to be used) and you must use cv::Mat instead.

Regarding the problem: Are you sure that you compiled OpenCV with proper ffmpeg (or any other video library) support? Make sure you have installed needed codecs and then recompile your opencv with necessary flags. Might help.

Make sure that the output of opencv installation cmake includes the similar text:

found gstreamer-base-0.10
GTK+ 2.x: YES
FFMPEG: YES
GStreamer: YES
V4L/V4L2: Using libv4l

PS. FFMPEG: YES

Answer 2

i had same problem, then i use class VideoCapture instead,

http://docs.opencv.org/modules/highgui/doc/reading_and_writing_images_and_video.html?highlight=videocapture#VideoCapture

Answer 3

I guess not right codecs are installed. We need to install correct Codecs following the suggestion from OpenCV at http://docs.opencv.org/modules/highgui/doc/reading_and_writing_images_and_video.html. Check the VideoWriter::VideoWriter section. We need Video Codecs by FOURCC at http://www.fourcc.org/codecs.php. Be careful. The installation may install garbage as well as codecs. Not all codecs are recognized. At least now I have mpeg4 and DivX and can open Megamind.avi, used by OpenCV's own demo program.