VideoCapture always returns False in Python OPENCV [Linux]

Question

Every time that I use VideoCapture trying to access the frames from a video file, the return value (ret) is false. See the sample code below:

cap = cv2.VideoCapture('asd.mkv')
    vid = []
    while True:
        ret, img = cap.read()
        if not ret: # Always happens
            break
        vid.append(cv2.resize(img, (171, 128)))

I have already tried absolutely everything I could find today by googling, including the OpenCV guide and this long issue on Github. Also, I read some solutions involving moving ffmpeg dll files, but that only was in the case of Windows.

Any ideas? Because I defenitely ran out of them.

Can you try providing a full qualified file path to `cv2.VideoCapture('full/path/to/vid.mkv')` — ZdaR, Apr 03 '17 at 04:39
@chbchb55 No, it contains `None`. @ZdaR already tried that, and also different video formats. — Daniyal Shahrokhian, Apr 06 '17 at 14:22
I found your problem, http://stackoverflow.com/questions/20852514/list-file-extensions-supported-by-opencv, you can't use that format. The only format that VideoCapture works with is 'avi', 'mkv' isn't supported — Andria, Apr 06 '17 at 20:00

score 2 · Answer 1 · edited Jun 20 '20 at 09:12

2

For future reference: installing opencv with pip does not work with ffmpeg.

From the opencv-python FAQ:

Q: Why I can’t open video files on GNU/Linux distribution X or on macOS?

A: OpenCV video I/O depends heavily on FFmpeg. Manylinux and macOS OpenCV binaries are not compiled against it. The purpose of these packages is to provide as easy as possible installation experience for OpenCV Python bindings and they should work directly out-of-the-box. Adding FFmpeg as an additional dependency without a “universal” FFmpeg build (e.g. LGPL licensed build like in the Windows wheels) the goal is considerably harder to achieve. This might change in the future.

Solutions:

Build from source (docs). This worked for me.
Use scikit-video as a workaround (Github).

edited Jun 20 '20 at 09:12

Community

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answered Oct 26 '17 at 05:26

qwr

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could you please explain what "compiled against" means? Does it mean we can install ffmpeg ourselves? or does it mean it has to be included in the opencv package – Adam B Apr 27 '20 at 19:40
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@AdamB I don't know the internals but it means OpenCV when compiling had to include ffmpeg to enable ffmpeg features. I believe you have to compile yourself with ffmpeg enabled. – qwr Apr 27 '20 at 20:11
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A while ago I made a guide for ubuntu installing from source that may help https://askubuntu.com/a/1150443/477026 – qwr Apr 27 '20 at 20:14
Great! I’ll try that out. – Adam B Apr 27 '20 at 22:20

score 0 · Accepted Answer · answered Apr 07 '17 at 16:14

0

The problem was at my IDE (Visual Studio Code) and the association with bin files when installing OpenCV... my bad. This guide worked flawlessly.

answered Apr 07 '17 at 16:14

Daniyal Shahrokhian

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VideoCapture always returns False in Python OPENCV [Linux]

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