Question

I’m using openCV to split a video into frames. For that I need the fps and duration. Both of these value return 1 when asking them via cvGetCaptureProperty.

I’ve made a hack where I use AVURLAsset to get the fps and duration, but when I combine that with openCV I get only a partial video. It seems like it’s missing frames.

This is my code right now:

while (cvGrabFrame(capture)) {
    frameCounter++;

    if (frameCounter % (int)(videoFPS / MyDesiredFramesPerSecond) == 0) {
      IplImage *frame = cvCloneImage(cvRetrieveFrame(capture));
      // Do Stuff     
    }

    if (frameCounter > duration*fps)
    break; // this is here because the loop never stops on its own
}

How can I get all the frames of a video using openCV on iOS? (opencv 2.3.2)

Answer 1

According to the documentation you should check the value returned by cvRetrieveFrame(), if a null pointer is returned you’re at the end of the video sequence. Then you break the loop when that happens, instead of relying on the accuracy of FPS*frame_number.