Python opencv videocapture fails to open file with python3 but works with python2

Question

I've tried numerous things including building from source (both opencv and ffmpeg with codecs) and nothing seems to help. I have a mp4 file that works fine with the python2.7 environment, but fails to load with python 3.5.

I know I have different builds installed, but I can't figure out why opencv fails to load for the python3.5 environment. I've checked paths, etc. I can't find anything amiss.

Python 2.7.12:

Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
>>> cv2.__version__
'3.3.1'
>>> a=cv2.VideoCapture("Serenity.mp4")
>>> a.isOpened()
True

Python 3.5.2:

Python 3.5.2 (default, Sep 14 2017, 22:51:06) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
>>> cv2.__version__
'3.3.0'
>>> a=cv2.VideoCapture("Serenity.mp4")
>>> a.isOpened()
False

I've done the following:

Uninstalled python and python3, and opencv
Checked paths to modules
video plays fine on vlc and ffmpeg has no problems
test code using python2.7 plays video fine via opencv
tried answers found here: Can't open video using opencv
Tried this too Python OpenCV : VideoCapture differences between Python 2.7 to Python 3.5

Information on video sample:

ffprobe version 3.4 Copyright (c) 2007-2017 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.5) 20160609
  configuration: --enable-pic
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x3d57b00] stream 0, timescale not set
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Serenity.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isomavc1
    creation_time   : 2007-05-30T05:20:31.000000Z
    genre           : Trailer
    artist          : Universal Pictures
    title           : Serenity - HD DVD Trailer
    date            : 2005
  Duration: 00:02:19.71, start: 0.000000, bitrate: 4802 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 4674 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc (default)
    Metadata:
      creation_time   : 2007-05-30T05:20:31.000000Z
      handler_name    : GPAC ISO Video Handler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      creation_time   : 2007-05-30T05:20:34.000000Z
      handler_name    : GPAC ISO Audio Handler
    Stream #0:2: Video: mjpeg, yuvj420p(pc, bt470bg/unknown/unknown), 240x240 [SAR 1:1 DAR 1:1], 90k tbr, 90k tbn, 90k tbc

Edit: I've also tried compiling from source using the methods outlined here based on suggestions from the comments (and swapping the .so file): https://www.pyimagesearch.com/2016/10/24/ubuntu-16-04-how-to-install-opencv/

solved: After many attempts, I had to just wipe my Lubuntu 16.04.3 system and rebuild it. See detailed answer below.

This post may help, [link](https://github.com/opencv/opencv/issues/8471) — Gumboy, Nov 25 '17 at 02:31

score 0 · Accepted Answer · answered Dec 01 '17 at 02:48

After a fresh lubuntu install with the dev packages added I was able to compile opencv 3.3.1 successfully and then I opened python3:

import cv2
cv2.__version__

Reported 3.3.0 which was wrong

cv2.__file__

told me the import location, so I renamed that cv2.cpython-35m-x86_64-linux-gnu.so.old. Then using

find /usr/local/lib/ -type f -name "cv2*.so"

I located the one I just built and moved it to the cv2.file location and this worked.

FYI -- also compiled opencv using the following set of commands:

#Remove any previous installations of x264</h3>
sudo apt-get remove x264 libx264-dev

#Install dependencies now

sudo apt-get install build-essential checkinstall cmake pkg-config yasm
sudo apt-get install git gfortran
sudo apt-get install libjpeg8-dev libjasper-dev libpng12-dev

# LUbuntu 16.04
sudo apt-get install libtiff5-dev

sudo apt-get install libavcodec-dev libavformat-dev libswscale-dev libdc1394-22-dev
sudo apt-get install libxine2-dev libv4l-dev
sudo apt-get install libgstreamer0.10-dev libgstreamer-plugins-base0.10-dev
sudo apt-get install qt5-default libgtk2.0-dev libtbb-dev
sudo apt-get install libatlas-base-dev
sudo apt-get install libfaac-dev libmp3lame-dev libtheora-dev
sudo apt-get install libvorbis-dev libxvidcore-dev
sudo apt-get install libopencore-amrnb-dev libopencore-amrwb-dev
sudo apt-get install x264 v4l-utils

# Optional dependencies
sudo apt-get install libprotobuf-dev protobuf-compiler
sudo apt-get install libgoogle-glog-dev libgflags-dev
sudo apt-get install libgphoto2-dev libeigen3-dev libhdf5-dev doxygen

# clone it
git clone https://github.com/opencv/opencv.git
cd opencv 
git checkout 3.3.1 
cd ..

git clone https://github.com/opencv/opencv_contrib.git
cd opencv_contrib
git checkout 3.3.1
cd ..

cd opencv
mkdir build
cd build

cmake -D CMAKE_BUILD_TYPE=RELEASE \
      -D CMAKE_INSTALL_PREFIX=/usr/local \
      -D INSTALL_C_EXAMPLES=ON \
      -D INSTALL_PYTHON_EXAMPLES=ON \
      -D WITH_TBB=ON \
      -D WITH_V4L=ON \
      -D WITH_QT=ON \
      -D WITH_OPENGL=ON \
      -D OPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules \
      -D BUILD_EXAMPLES=ON ..

# depending on your processor cores use -j2 for 2 cores, -j4 for 4
make -j2
sudo make install

Python opencv videocapture fails to open file with python3 but works with python2

1 Answers1