VideoWriter fps parameter

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@berak thanks for the reply. Is it possible to provide some clarifications on what is happening on the saved video when the parameter fps is different to the real fps? Is there an up-sampling or down-sampling procedure? In other words, how the saved frames are distributed? Thanks again.

again, the writer does not know anything about "real" fps. there is no magic under the hood. if you say: 25 fps, 25 frames per second will be played later, that's it. no sampling of any kind, uniform distribution.

Absolutely, berak.

I am also trouble in this issue. I set 10 fps in constructor function of VideoWriter, but I call videoWriter.write(frame) function more than 10 times per second. So what is the real fps in my saved video and which frames are saved?

videoWriter = cv2.VideoWriter('video_demo.avi', cv2.cv.CV_FOURCC('M', 'J', 'P', 'G'), 10, size)  

success, frame = videoCapture.read()  

while success :  
    cv2.imshow("Video demo", frame) 
    videoWriter.write(frame) 
    success, frame = videoCapture.read()  
    if cv2.waitKey(1) == 27: 
        break  # esc to quit

@jsplyy -- please do not post answers on this site, if you have a question or comment, thank you.

( and your video will run at 10 fps, but it will look faster or slower. again, all you can do is 1. make a reasonable assumption, on how fast your processing is, and how many frames you can render per second, and use (slightly less than) that for the fps. 2. adjust the actual framerate, using waitKey(some_millis_left_over) )