OpenCV Python视频播放 - 如何为cv2.waitKey()设置正确的延迟

Question

我使用以下代码捕获视频文件,翻转并保存.

#To save a Video File

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object
fourcc = cv2.cv.CV_FOURCC(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))

while(cap.isOpened()):
    ret, frame = cap.read()
    if ret==True:
        frame = cv2.flip(frame,0)

        # write the flipped frame
        out.write(frame)

        cv2.imshow('frame',frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    else:
        break

# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()

该程序将输出保存为output.avi

现在,为了播放视频文件,我使用了以下程序

#Playing Video from File

import numpy as np
import cv2

cap = cv2.VideoCapture('output.avi')

print cap.get(5) #to display frame rate of video
#print cap.get(cv2.cv.CV_CAP_PROP_FPS)

while(cap.isOpened()): 
    ret, frame = cap.read()

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY) #convert to grayscale

    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'): 
        break

cap.release()
cv2.destroyAllWindows()

该程序播放从第一个程序保存的视频文件output.avi.问题是,这个视频出现了快进.所以,我尝试更改cv2.waitKey()的延迟值.当我放100时,视频看起来很好.我怎么知道放在哪个值？它应该与帧速率有关吗？我检查了output.avi的帧速率(见第二个程序中的cap.get(5)行)并得到20.但如果我使用20作为cv2.waitKey()的延迟,则视频仍然太快.

任何帮助,将不胜感激.

Answer 1

该函数cv.waitKey([, delay])无限地等待键事件(当延迟<= 0时)或等待延迟毫秒,当它为正时.

如果FPS等于20,那么您应该在连续帧之间等待0.05秒.所以放在delay <= 0后面delay,它将以正常速度显示.