Python OpenCV视频录制快速转发

Question

I've made a short script that is the beginings of a rubik's cube timer, but when I play back the recorded video it is extremely sped up.

My webcam is a 'Creative Labs Live! Cam Chat HD' and has a resolution of 1280*720 pixels, Side note; when I try and run the script encoding in that resolution playback fails, and a framerate of 30 fps.

Below is the code and a link of a video demonstrating the effect.

from time import clock as t
import time
import cv2
import numpy as np
cap = cv2.VideoCapture(0)
fourcc = cv2.VideoWriter_fourcc(*"XVID")
out = cv2.VideoWriter("output.avi", fourcc, 30.0, (640, 480))
timing = False

while True:
    ret, frame = cap.read()
    #frame = cv2.flip(frame, 1)
    cv2.imshow("frame", frame)

    if timing:
        out.write(frame)

    if cv2.waitKey(1) & 0xFF == ord(" "):
        if timing:
            after = t()
            break
        else:
            timing = True
            start = t()

cap.release()
out.release()
cv2.destroyAllWindows()

print(after - start)

Example of the accelerated video.

Answer 1

You are writing output at 30 fps,and your webcam possibly not recording at 30 fps. Thats why your video is fast. Find proper fps and output will be normal.

Find framerate like fps=cap.get(cv2.CAP_PROP_FPS) for opencv >=3

Answer 2

I encountered the same issues. I think it was caused by the write action. You tried to save the video at 30fps, but the write action can't handle that. For example, you want to save 180frame at 30fps, that video should be 6 seconds. But the write action can only save 10 frames per second, so 20 frames will be dropped per second. But the video still played at 30fps, so 6 seconds video becomes 2 seconds. Seems faster.