javacv: grabber.getFrameRate() return 0 - javacv

Question

I have used javacv for my project to deal with avi.
The video shows faster than normal, I want to get the fps to set the speed of the video. But grabber.getFrameRate() return 0, as the same with grabber.getLengthInFrames() and grabber.getSampleRate(), can anyone tell me why?
code snippet below:
FrameGrabber grabber = new OpenCVFrameGrabber("sample.avi");
double fps=grabber.getFrameRate();
System.out.println(fps);
//int n=grabber.getLengthInFrames();
//int f=grabber.getSampleRate();
CvMemStorage storage = CvMemStorage.create();
grabber.start();
grabbedImage = grabber.grab();
while (frame.isVisible() && (grabbedImage = grabber.grab()) != null)
{
BufferedImage bfimg = grabbedImage.getBufferedImage();
frame.showImage(bfimg);
frame.waitKey((int)(1000/fps));
cvClearMemStorage(storage);
}
grabber.stop();

Answer 1

you must call after start();
maybe you can
FrameGrabber grabber = new OpenCVFrameGrabber("sample.avi");
grabber.start();
double fps=grabber.getFrameRate();

Answer 2

I use this code to record mp4 video:
public static void main(String[] args) {
IplImage image;
CanvasFrame canvas = new CanvasFrame("Web Cam");
try {
OpenCVFrameGrabber grabber = new OpenCVFrameGrabber(0);
grabber.start();
IplImage grabbedImage = grabber.grab();
canvas.setCanvasSize(grabbedImage.width(), grabbedImage.height());
System.out.println("framerate = " + grabber.getFrameRate());
grabber.setFrameRate(grabber.getFrameRate());
FFmpegFrameRecorder recorder = new FFmpegFrameRecorder("c:/demo.mp4", 320, 240);
recorder.setVideoCodec(13);
recorder.setFormat("mp4");
recorder.setPixelFormat(avutil.AV_PIX_FMT_YUV420P);
recorder.setFrameRate(10);
recorder.setVideoBitrate(5*1024);
recorder.start();
System.out.println("framerate = " + grabber.getFrameRate());
while (canvas.isVisible() && (grabbedImage = grabber.grab()) != null) {
canvas.showImage(grabbedImage);
recorder.record(grabbedImage);
}
recorder.stop();
grabber.stop();
canvas.dispose();
} catch (Exception e) {
e.printStackTrace();
}
}

Answer 3

I tried this in a webcam example and it worked:
double time1,time2;
// your loop
while(....){
time1=System.currentTimeMillis(); // add this first in the loop
//code here
.
.
.
.
time2=System.currentTimeMillis(); // add this at the end of the loop
System.out.println("framerate = " + 1/(((time2-time)/1000)%60))
} //end of loop
In case of webcam example with code for webcam found:
http://opencvlover.blogspot.com/2012/05/accessing-webcam-using-javacv.html
it looks like this :
IplImage img
while (...) {
time1=System.currentTimeMillis(); // add this first in the loop
//inser grabed video fram to IplImage img
img = grabber.grab();
.
.
.
.
//Show video frame in canvas
canvas.showImage(img);
time2=System.currentTimeMillis(); // add this at the end of the loop
System.out.println("framerate = " + 1/(((time2-time)/1000)%60))
} //end of loop
.
.
.