python上的cv2.VideoCapture

Question

I am running the following code:

import numpy as np
import cv2
import os

count = 0

cap = cv2.VideoCapture("/home/simon/PROJECT/real_data/00000020.mp4")

while not cap.isOpened():
    cap = cv2.VideoCapture("./00000020.mp4")
    cv2.waitKey(1000)
    print "Wait for the header"

pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
while True:
    flag, frame = cap.read()
    if flag:
        # The frame is ready and already captured
        cv2.imshow('video', frame)
        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
        print str(pos_frame)+" frames"
    else:
        # The next frame is not ready, so we try to read it again
        cap.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, pos_frame-1)
        print "frame is not ready"
        # It is better to wait for a while for the next frame to be ready
        cv2.waitKey(1000)

    if cv2.waitKey(10) & 0xFF == 27:
        break
    if cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES) ==       cap.get(cv2.cv.CV_CAP_PROP_FRAME_COUNT):
    # If the number of captured frames is equal to the total number of frames,
    # we stop
    break


if ret == True:
    frame = cv2.VideoCapture.grab()
    frame = 'frame%d' % count 

    cv2.imwrite('frame%d.png', frame)

    count += 1
else:
    print 'stopped at' + count
    break

And whenever I run it, it loops on the while not loop, printing "wait for header". There is never an error code or anything like that either.

I have tried to run it as a more simple piece of code, where it doesnt have all these checks, and again that doesn't throw any errors.

I am attempting to run this code to open a video, and then save the frames as png files throughout the video.

Does anyone spot any particular problems with the code? Or alternatively does anyone know a piece of code that would do what i want more efficiently, as I have trawled through google searches and stack overflow a lot recently and haven't found anything

Thanks in advance Panda

Answer 1

You need to include a couple of DLLs in your python directory in order to play videos. Please see this for details:

https://li8bot.wordpress.com/2014/07/09/opencvpython-part-1-working-with-videos/