GStreamer demo | Python Fiddle

#!/usr/bin/python -u

import signal
import gi
from gi.repository import GObject, Gtk, Gdk, GLib, GdkX11

gi.require_version('Gst', '1.0')
from gi.repository import Gst
from gi.repository import GstVideo

VIDEOSINK = 'videoconvert ! xvimagesink {xvimagesinkparam} '
GST_PLAY_PIPELINE = 'filesrc location="{location}" ! decodebin ! videoconvert ! queue ! ' + \
    'videomixer name="mix" sink_1::xpos=1019 sink_1::ypos=571 ! ' + VIDEOSINK + ' name="videosink" ' + \
    'v4l2src device={camera} ! videoconvert ! videoscale ! queue ! video/x-raw,width=258,height=147 ! mix. '

# curl -O https://test-videos.co.uk/vids/bigbuckbunny/mp4/h264/720/Big_Buck_Bunny_720_10s_1MB.mp4

class Demo(object):
    def __init__(self):
        self.pipeline = None
        self.bus = None

GObject.threads_init()
        Gst.init(None)

def start(self, video_device):

self.win = Gtk.Window.new(Gtk.WindowType.TOPLEVEL)
        self.win.set_default_size(720, 405)
        self.win.show_all()
        GLib.unix_signal_add(GLib.PRIORITY_DEFAULT, signal.SIGINT, self.stop)

mock = 'Big_Buck_Bunny_720_10s_1MB.mp4'
        pipedesc = GST_PLAY_PIPELINE.format(location=mock, xvimagesinkparam='sync=false', camera=video_device)
        self.pipeline = Gst.parse_launch(pipedesc)

self.bus = self.pipeline.get_bus()
        self.bus.add_signal_watch()
        self.bus.connect("message", self.on_message)
        self.bus.enable_sync_message_emission()
        self.bus.connect("sync-message::element", self.on_sync_message)
        self.pipeline.set_state(Gst.State.PLAYING)

mixer = self.pipeline.get_by_name('mix')
        mixerpad = mixer.get_static_pad('sink_0')
        mixerpad.add_probe(Gst.PadProbeType.EVENT_DOWNSTREAM, self.playback_eos_cb, None)

Gtk.main()

def stop(self):
        self.pipeline.set_state(Gst.State.NULL)
        Gtk.main_quit()

def playback_eos_cb(self, pad, info, user_data):

if info.get_event().type == Gst.EventType.EOS:
            print('#### EOS EOS EOS EOS ####')
            status, running_time = self.pipeline.query_position(Gst.Format.TIME)
            print('[playback_eos_cb] query_position:', status, running_time)

decodebin = self.pipeline.get_by_name('decodebin0')
            status = decodebin.seek_simple(Gst.Format.TIME, Gst.SeekFlags.NONE, 0)

print('[playback_eos_cb] set_offset:', running_time / Gst.SECOND)
            pad.set_offset(running_time / Gst.SECOND)

return Gst.PadProbeReturn.PASS

def on_message(self, bus, msg):
        if msg.type == Gst.MessageType.ERROR:
            print('!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!')
            print(msg.parse_error())
            print('!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!')

def on_sync_message(self, bus, msg):
        name = msg.get_structure().get_name()
        if name == 'prepare-window-handle':
            xid = self.win.get_property('window').get_xid()
            msg.src.set_window_handle(xid)

app = Demo()
app.start('/dev/video2')

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