GStreamer Qt6GLVideoItem cannot be imported by QML with PySide6

djboris · wrote on 6 Apr 2025, 11:57

Hi community,

I'm porting an application from PyQt5 to PyQt6/PySide6.

With Qt5 it used the QMediaPlayer for playing an RTP stream processed with GStreamer like:

self.mm = QMediaPlayer(None)
self.mm.setMedia(QMediaContent(QUrl("gst-pipeline: ..."))

As GStreamer pipelines are not supported anymore directly in Qt6-Multimedia, I switched the GUI to QML in order to use Qt6GLVideoItem.

But I always get the following error while running the attached minimal reproduction as you can see below:

$ ./repro.py 
GStreamer: (major=1, minor=26, micro=0, nano=0), Qt: 6.8.3
QQmlApplicationEngine failed to load component
file:///home/djboris/MASKED/repro.qml:4:1: module "org.freedesktop.gstreamer.Qt6GLVideoItem" is not installed

This happens with the Arch Linux GStreamer package (version 1.26.0, gst-plugins-good, gst-plugin-qml6, gst-plugin-qmlgl installed).
The same issue exists with the GStreamer project compiled from main@7d51dc615d6ecae51e41dd8adbcf8c9a5ce74a09 with Qt6 support enabled and running in gst-dev.py-environment.

I also tried to run it on a Debian system with the distributed packages but had no luck with making it work.

Now my Qt debugging skills are exhausted as I don't understand how the import statement of org.freedesktop.gstreamer.Qt6GLVideoItem can find the GStreamer component as there is no qmldir present in the GStreamer installation. It looks like there is a matching symbol in /usr/lib/gstreamer-1.0/libgstqmlgl.so but how (and if) this can be imported in QML correctly.

Finally, my questions are:

What could be the cause of the import issue? Or: How does the QML import of Qt6GLVideoItem work, so I could further narrow down my issue
Are there better ways to show an RTP stream in Qt6?

A solution without QML is also fine. Migration from Python to C++ is possible, but not preferred. The code snippets were inspired from the GStreamer examples.

#!/usr/bin/env python3
# This is repro.py

import sys
import signal
signal.signal(signal.SIGINT, signal.SIG_DFL)
from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtCore import qVersion

import gi
gi.require_version("GLib", "2.0")
gi.require_version('Gst', '1.0')
from gi.repository import Gst, GLib


def main(args):
    app = QGuiApplication(args)

    pipeline = Gst.parse_launch("videotestsrc ! glupload ! qmlgloverlay name=o ! gldownload ! videoconvert ! qmlglsink name=sink")
    engine = QQmlApplicationEngine()
    engine.quit.connect(app.quit)
    engine.load('repro.qml')

    return app.exec()


if __name__ == '__main__':
    Gst.init(sys.argv)
    print(f'GStreamer: {Gst.version()}, Qt: {qVersion()}')
    sys.exit(main(sys.argv))

// This is repro.qml
import QtQuick 6.0
import QtQuick.Controls 6.0
import org.freedesktop.gstreamer.Qt6GLVideoItem 1.0

ApplicationWindow {
    visible: true
    width: 600
    height: 500
    title: "Repro"

    Text {
        anchors.centerIn: parent
        text: "Repro"
        font.pixelSize: 24
    }

    Qt6GLVideoItem {
        id: video
        objectName: "inputVideoItem"
        anchors.centerIn: parent
        width: parent.width
        height: parent.height
    }
}

Jesus Gazol · wrote on 16 Apr 2025, 06:32

Hi, having the same problem with Ubuntu 24.04, some debug logs attached:

0:00:00.000056816 240736      0xb9959e0 INFO                GST_INIT gst.c:574:init_pre: Initializing GStreamer Core Library version 1.24.2
0:00:00.000080340 240736      0xb9959e0 INFO                GST_INIT gst.c:575:init_pre: Using library installed in /usr/lib/x86_64-linux-gnu
0:00:00.000086081 240736      0xb9959e0 INFO                GST_INIT gst.c:593:init_pre: Linux jesus-HP-ZBook 6.11.0-17-generic #17~24.04.2-Ubuntu SMP PREEMPT_DYNAMIC Mon Jan 20 22:48:29 UTC 2 x86_64
0:00:00.000172642 240736      0xb9959e0 INFO                GST_INIT gstmessage.c:129:_priv_gst_message_initialize: init messages
0:00:00.000314487 240736      0xb9959e0 INFO                GST_INIT gstcontext.c:86:_priv_gst_context_initialize: init contexts
0:00:00.000365642 240736      0xb9959e0 INFO      GST_PLUGIN_LOADING gstplugin.c:328:_priv_gst_plugin_initialize: registering 0 static plugins
0:00:00.000393865 240736      0xb9959e0 INFO      GST_PLUGIN_LOADING gstplugin.c:236:gst_plugin_register_static: registered static plugin "staticelements"
0:00:00.000399135 240736      0xb9959e0 INFO      GST_PLUGIN_LOADING gstplugin.c:238:gst_plugin_register_static: added static plugin "staticelements", result: 1
0:00:00.000417529 240736      0xb9959e0 INFO            GST_REGISTRY gstregistry.c:1918:ensure_current_registry: reading registry cache: ~/.cache/gstreamer-1.0/registry.x86_64.bin
0:00:00.007627994 240736      0xb9959e0 INFO            GST_REGISTRY gstregistrybinary.c:683:priv_gst_registry_binary_read_cache: loaded ~/.cache/gstreamer-1.0/registry.x86_64.bin in 0.007197 seconds
0:00:00.007716520 240736      0xb9959e0 INFO            GST_REGISTRY gstregistry.c:1785:scan_and_update_registry: Validating plugins from registry cache: ~/.cache/gstreamer-1.0/registry.x86_64.bin
0:00:00.008525830 240736      0xb9959e0 INFO      GST_PLUGIN_LOADING gstplugin.c:1630:gst_plugin_ext_dep_extract_env_vars_paths:<plugin191> ignoring environment variable 'DISPLAY' with content #0 '': either not an absolute path or not a path at all
0:00:00.008532823 240736      0xb9959e0 INFO      GST_PLUGIN_LOADING gstplugin.c:1630:gst_plugin_ext_dep_extract_env_vars_paths:<plugin191> ignoring environment variable 'DISPLAY' with content #1 '0': either not an absolute path or not a path at all
0:00:00.008537752 240736      0xb9959e0 INFO      GST_PLUGIN_LOADING gstplugin.c:1630:gst_plugin_ext_dep_extract_env_vars_paths:<plugin191> ignoring environment variable 'WAYLAND_DISPLAY' with content #0 'wayland-0': either not an absolute path or not a path at all
0:00:00.009375976 240736      0xb9959e0 INFO            GST_REGISTRY gstregistry.c:1877:scan_and_update_registry: Registry cache has not changed
0:00:00.009396565 240736      0xb9959e0 INFO            GST_REGISTRY gstregistry.c:1953:ensure_current_registry: registry reading and updating done
0:00:00.009411363 240736      0xb9959e0 INFO                GST_INIT gst.c:807:init_post: GLib runtime version: 2.80.0
0:00:00.009415140 240736      0xb9959e0 INFO                GST_INIT gst.c:809:init_post: GLib headers version: 2.80.0
0:00:00.009417664 240736      0xb9959e0 INFO                GST_INIT gst.c:811:init_post: initialized GStreamer successfully
INFO:root:qml: Qt 6.9.0 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 10.3.1 20210422 (Red Hat 10.3.1-1)) [Python limited API 3.12.3]
INFO:root:qml: Using built-in configuration: default
INFO:root:qml: loading ~/main2.qml
INFO:root:qml: Using attribute AA_ShareOpenGLContexts
INFO:root:qml: Gui application
QQmlApplicationEngine failed to load component ~/main2.qml:4:1: module "org.freedesktop.gstreamer.Qt6GLVideoItem" is not installed

JoeCFD · wrote on 16 Apr 2025, 11:25

https://forum.qt.io/topic/161751/qt6-gstreamer-cmake/2?_=1744802661208