Problem with GStreamer and WPEWebKit in Python3

Question

I want to create a program in Python that allows to edit text that moves and show on top of a video. I want to do that in a website overlay (WPEWebKit).

I have found some code to start a pipeline with wpe and gst-launch-1.0, problem is that when I run gst-launch-1.0 -v wpesrc location="https://gstreamer.freedesktop.org" ! queue ! glimagesink from https://gstreamer.freedesktop.org/documentation/wpe/wpesrc.html it says WARNING: erroneous pipeline: no element "wpesrc". I have checked and I have installed gstreamer1.0-plugins-bad.

The other challange is that I want to create it in a python application. Here's my code so far:

import threading
import time

import gi

gi.require_version("Gst", "1.0")

from gi.repository import Gst, GLib


Gst.init()

main_loop = GLib.MainLoop()
thread = threading.Thread(target=main_loop.run)
thread.start()

pipeline = Gst.parse_launch("videotestsrc ! decodebin ! videoconvert ! autovideosink")
pipeline.set_state(Gst.State.PLAYING)

try:
    while True:
        time.sleep(0.1)
except KeyboardInterrupt:
    pass

pipeline.set_state(Gst.State.NULL)
main_loop.quit()

I will be probably rewrite this because I want it in a GTK application.