无法在OpenCV上播放.h264视频？

Question

I captured a standard video from camera of Raspberry pi. The codec of the file is h264. To play the video I do:

import numpy as np
import cv2

cap = cv2.VideoCapture('foo.h264')

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

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

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

cap.release()
cv2.destroyAllWindows()

Video starts But stops after sometime throwing this error:

Traceback (most recent call last):
  File "play_video.py", line 9, in <module>
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.error: /home/nikhil/Downloads/opencv-2.4/modules/imgproc/src/color.cpp:3739: error: (-215) scn == 3 || scn == 4 in function cvtColor

My machine has Ubuntu 12.04. I played an .avi file it plays smoothly. Is the problem with the .h264 or with the OpenCV?

Answer 1

Your loop should check that frame is not-empty, and not that the video was opened successfully - this check should be done just once at the beginning.
When the frame after last is read frame is empty and you are then trying to convert it to gray.