Q: Gstreamer OpenCV issue I am able to stream a video source (BlackMagic Decklink Card) using gstreamer on Ubuntu 16.04 using the following command:
gst-launch-1.0 decklinkvideosrc mode=7 ! videoconvert ! xvimagesink

Now I wanted to use this stream in OpenCV 4.0.1, so I tried to use the VideoCapture() interface like this:
cap = cv2.VideoCapture('decklinkvideosrc mode=7 connection=0 ! videoconvert ! appsink',cv2.CAP_STREAMER)

I'm unable to get the stream, I get this error:

GStreamer: Error opening bin: no element "decklinkvideosrc"

Running:
gst-inspect-1.0 decklink

Gives the output:
Plugin Details:
 Name                     decklink
 Description              Blackmagic Decklink plugin
 Filename                 /usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstdecklink.so
 Version                  1.8.3
 License                  LGPL
 Source module            gst-plugins-bad
 Source release date      2016-08-19
 Binary package           GStreamer Bad Plug-ins
 Origin URL               https://launchpad.net/distros/ubuntu/+source/gst-plugins-bad1.0

 decklinkvideosrc: Decklink Video Source
 decklinkaudiosrc: Decklink Audio Source
 decklinkvideosink: Decklink Video Sink
 decklinkaudiosink: Decklink Audio Sink

 4 features:
 +-- 4 elements

