Meson devenv and Python Gst.parse_launch( pipeline )

CarlFK · August 25, 2026, 7:58pm

I build gst master and:

python3 -m venv venvs/veyepar --system-site-packages
videoteam@mo:~$ meson devenv -C gstreamer/builddir
[gstreamer-full] videoteam@mo:~$ gst-launch-1.0 decklink2srcbin device-number=1 ! fakesink

Works fine. good.

Then I try to use decklink2srcbin in my python app.

[gstreamer-full] videoteam@mo:~/gstreamer/builddir$ . ~/venvs/veyepar/bin/activate
(veyepar) [gstreamer-full] videoteam@mo:~/gstreamer/builddir$ python3 ~/gslevels.py --test 
...
  File "/home/videoteam/gslevels.py", line 42, in mk_pipe
    self.pipeline = Gst.parse_launch( pipeline )
                    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^
gi.repository.GLib.GError: gst_parse_error: no element "decklink2srcbin" (1)

github.com/CarlFK/veyepar

dj/lib/gslevels.py

master

#!/usr/bin/python

# gslevels.py
# report audio levels
# to figure out what files are messed up

# http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good-plugins/html/gst-plugins-good-plugins-level.html

# gst-launch-1.0 uridecodebin name=decode uri="file://$PWD/SC1ATK103.mov" ! audioconvert ! level name=wavelevel post-messages=true ! fakesink --messages

# gst-launch-1.0 filesrc location="SC1ATK105.mov" ! qtdemux ! audioconvert ! level name=wavelevel post-messages=true ! fakesink --messages

import optparse
import numpy
import os

import gi
gi.require_version('Gst', '1.0')
from gi.repository import Gst, GLib
Gst.init(None)

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(sorry i looking at my code hurts. “For better or for worse, Python makes it easy and fun to write bad code.”)

I doubt the python virtualenv is relevant - I activated it both before/after, no help.