read/write avi video on MAC using openCV - c

Question

I am trying to read avi video and write it again as it is without any change using openCV 2.4.0 on MAC 10.6.8
My videos is grayscale with frame_rate = 25 and Codec = 827737670 which is FFV1 (I guess)
The problem is ....
when I read and write the video as it is .... I see many changes in size and in color ...
After 3 or 4 times of writing I can see the video start to be (Pink) color !!!
I am not sure what is the problem !!!
this is my code for the people who interest
Appreciate your help in advance :D
Seereen
Note : I have on my computer FFMPEG V 0.11 (I do not know if this important)
{
int main (int argc, char * const argv[]) {
char name[50];
if (argc==1)
{
printf("\nEnter the name of the video:");
scanf("%s",name);
} else if (argc == 2)
strcpy(name, argv[1]);
else
{
printf("To run this program you should enter the name of the program at least, or you can enter the name of the program then the file name");
return 0;
}
cvNamedWindow( "Read the video", CV_WINDOW_AUTOSIZE );
// GET video
CvCapture* capture = cvCreateFileCapture( name );
if (!capture )
{
printf( "Unable to read input video." );
return 0;
}
double fps = cvGetCaptureProperty( capture,CV_CAP_PROP_FPS);
printf( "fps %f ",fps );
int codec = cvGetCaptureProperty( capture,CV_CAP_PROP_FOURCC);
printf( "codec %d ",codec );
// Read frame
IplImage* frame = cvQueryFrame( capture );
// INIT the video writer
CvVideoWriter *writer = cvCreateVideoWriter( "x7.avi", codec, fps, cvGetSize(frame),1);
while(1)
{
cvWriteFrame( writer, frame );
cvShowImage( "Read the video", frame );
// READ next frame
frame = cvQueryFrame( capture );
if( !frame )
break;
char c = cvWaitKey(33);
if( c == 27 )
break;
}
// CLEAN everything
cvReleaseImage( &frame );
cvReleaseCapture( &capture );
cvReleaseVideoWriter( &writer );
cvDestroyWindow( "Read the video" );
return 0;}
}

Answer 1

Check this list of fourcc codes, and search for the uncompressed ones, like HFYU.
You also might find this article interesting: Truly lossless video recording with OpenCV.
EDIT:
I have a Mac OS X 10.7.5 at my disposal and since you gave us the video for testing I decided to share my findings.
I wrote the following source code for testing purposes: it loads your video file and writes it to a new file out.avi while preserving the codec information:
#include <cv.h>
#include <highgui.h>
#include <iostream>
int main(int argc, char* argv[])
{
// Load input video
cv::VideoCapture input_cap(argv[1]);
if (!input_cap.isOpened())
{
std::cout << "!!! Input video could not be opened" << std::endl;
return -1;
}
// Setup output video
cv::VideoWriter output_cap("out.avi",
input_cap.get(CV_CAP_PROP_FOURCC),
input_cap.get(CV_CAP_PROP_FPS),
cv::Size(input_cap.get(CV_CAP_PROP_FRAME_WIDTH), input_cap.get(CV_CAP_PROP_FRAME_HEIGHT)));
if (!output_cap.isOpened())
{
std::cout << "!!! Output video could not be opened" << std::endl;
return -1;
}
// Loop to read from input and write to output
cv::Mat frame;
while (true)
{
if (!input_cap.read(frame))
break;
output_cap.write(frame);
}
input_cap.release();
output_cap.release();
return 0;
}
The output video presented the same characteristics of the input:
Codec: FFMpeg Video 1 (FFV1)
Resolution: 720x480
Frame rate: 25
Decoded format: Planar 4:2:0 YUV
and it looked fine when playing.
I'm using OpenCV 2.4.3.

Answer 2

I figure out the problem ,,,,,
The original videos written in YUV240 pixel format (and it is gray)
the openCV read the video on BGR by default , so each time when I read it the openCV convert the pixel values to BGR
after few time of reading and writing , the error start to be bigger (because the conversion operation)
that why the pixels values change .....and I see the video pink !
The Solution is , read and write this kind of videos by FFMPEG project which provide YUV240 and many other format
there is a code can do this operation in the tutorial of FFMPEG
I hope this can help the others who face similar problem