Install gstreamer support for opencv python package

I have built my own opencv python package from source.

import cv2
print(cv2.__version__)

prints: 3.4.5

Now the issue I am facing is regarding the use of gstreamer from the VideoCapture class of opencv. I am trying to get this mimimum working example running on python3

cap = cv2.VideoCapture("videotestsrc ! appsink")

if not cap.isOpened():
    print("Cannot capture test src. Exiting.")
    quit()

while True:
    ret, frame = cap.read()
    if ret == False:
        break
    cv2.imshow("CVtest",frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

Capture fails, producing my print above (see if statement). I checked:

import cv2
print(cv2.getBuildInformation())

prints:

Video I/O:
DC1394:                      NO
FFMPEG:                      NO
  avcodec:                   NO
  avformat:                  NO
  avutil:                    NO
  swscale:                   NO
  avresample:                NO
GStreamer:                   NO
libv4l/libv4l2:              NO
v4l/v4l2:                    linux/videodev2.h

Seeing that, it made absolute sense that my gstreamer pipeline didn't work. I ensured WITH_GSTREAMER was set to ON during ccmake of OpenCV (which it already was). Still the issue maintained. I even tried setting WITH_GSTREAMER_0_10 to ON as well. Still no luck having gstreamer enabled from the cv2 python module.

Before anyone suggests using pip3 to install cv2. I tried that, too. The issue with getting the package from pip is, it doesn't let you configure gstreamer support at all.

Can anyone provide help here?

Solution

I was able to solve the issue, with a bit of help from the opencv support forum. Looking at the cmake output hints at the problem:

-- Checking for module 'gstreamer-base-0.10'
--   No package 'gstreamer-base-0.10' found
-- Checking for module 'gstreamer-video-0.10'
--   No package 'gstreamer-video-0.10' found
-- Checking for module 'gstreamer-app-0.10'
--   No package 'gstreamer-app-0.10' found
-- Checking for module 'gstreamer-riff-0.10'
--   No package 'gstreamer-riff-0.10' found
-- Checking for module 'gstreamer-pbutils-0.10'
--   No package 'gstreamer-pbutils-0.10' found

During ccmake, I had set both WITH_GSTREAMER as well as WITH_GSTREAMER_0_10 to ON. Seems that cmake prefers the gstreamer0.10 flag over the one for gstreamer1.0. Since I only have gstreamer1.0 installed, opencv entirely failed setting up the gstreamer dependencies.

I made sure to whipe all previously deployed binaries:

cd <opencv-src>/build 
sudo make uninstall

Then I simply reinstalled, with the adjusted settings (given my knowledge above):

ccmake ..
make -j8
sudo make install

when I

import cv2
print(cv2.getBuildInformation())

my console now outputs

Video I/O:
DC1394:                      NO
FFMPEG:                      NO
  avcodec:                   NO
  avformat:                  NO
  avutil:                    NO
  swscale:                   NO
  avresample:                NO
GStreamer:                   
  base:                      YES (ver 1.8.3)
  video:                     YES (ver 1.8.3)
  app:                       YES (ver 1.8.3)
  riff:                      YES (ver 1.8.3)
  pbutils:                   YES (ver 1.8.3)
libv4l/libv4l2:              NO
v4l/v4l2:                    linux/videodev2.h

Bottom line is, do not set WITH_GSTREAMER_0_10 to ON during cmake, if you actually want gstreamer1.0. In that case you must only set WITH_GSTREAMER ON