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(python) VideoCapture() returns zero for all CV cap props

asked 2016-09-08 04:13:10 -0500

Hello everybody,

I am trying to create a plot as overlay in my video (uisng openCV and matplotlib). The first thing would be to detect the frames of the video. This is what I am trying to do:

cap = cv2.VideoCapture('C:/PyDev/workspace/MyProject/src/files/video.mp4')
pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)

Using the debugger, the variable cap hold the value

 VideoCapture: <VideoCapture 000000000425D310>

but the value of pos_frame is 0.0.

I already tried other videos and other formats. Also I installed the K-Lite Codec Pack. Unfortunately it didn't help. I don't really understand if the video is loaded successfully (I think yes, as cap is not empty). Also calling

cap.grab()

retuns False.

Does anyone know how to solve this problem?

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Not sure what you did here VideoCapture: <VideoCapture 000000000425D310>, but did you already tried visualising the frames first?

StevenPuttemans gravatar imageStevenPuttemans ( 2016-09-08 04:49:45 -0500 )edit
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1st thing: please check, if your video was loaded: cap.isOpened() == True

(the VideoCapture object itself will always be valid, video loaded or not)

berak gravatar imageberak ( 2016-09-08 05:01:29 -0500 )edit
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@StevenPuttemans: This is just the value of the cap variable during runtime. I can't visualize the frames, as the video seems not to be loaded correctly. @berak: Thanks, I tried it and isOpened() returns False. Which means there is a problem loading the video. The path is correct. What else could I try?

user7761 gravatar imageuser7761 ( 2016-09-08 05:11:01 -0500 )edit
1

to rule out a codec issue, could you try one of the vids from opencv/samples/data ? e.g. the 768x576.avi ?

(if that works, you know, it's a mp4 problem, and you have to hunt for codecs to install.

berak gravatar imageberak ( 2016-09-08 05:17:07 -0500 )edit

Thank you very much @berak. By using the sample video I could find out, that this is a codec problem. Installed K-Lite Codec Pack and Windows 7 Codec Pack but unfortunetaly it didn't help. Can you give an advice, in which direction i should go with my research?

user7761 gravatar imageuser7761 ( 2016-09-08 05:36:10 -0500 )edit

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answered 2016-09-08 06:09:56 -0500

I converted the video to avi using the following ffmpeg command: ffmpeg -i input.mp4 -c:v libxvid output.avi. It works fine now. Many thanks for the help!

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My video is already in .avi but still same problem. I can read the first frame and display it however cv2.CAP_PROP_FRAME_COUNT returns 0.0

Akanksha Rathore gravatar imageAkanksha Rathore ( 2019-02-25 06:15:25 -0500 )edit
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Asked: 2016-09-08 04:12:04 -0500

Seen: 1,550 times

Last updated: Sep 08 '16