PoC: Read from video capture device using xdg-desktop-portals, pipewire and gstreamer and consume the video with VidGear/OpenCV

main.py

#!/usr/bin/python3

import re
import numpy as np
import dbus
from dbus.mainloop.glib import DBusGMainLoop
from time import sleep
from vidgear.gears import WriteGear

from gstreamer import GstContext, GstPipeline, GstApp, Gst, GstVideo
import gstreamer.utils as gst_utils
from typing import Any

DBusGMainLoop(set_as_default=True)
Gst.init(None)

bus = dbus.SessionBus()
request_iface = 'org.freedesktop.portal.Request'
camera_iface = 'org.freedesktop.portal.Camera'

fd = None


request_token_counter = 0
sender_name = re.sub(r'\.', r'_', bus.get_unique_name()[1:])

writer = WriteGear(output_filename="test.mp4")


def new_request_path():
    global request_token_counter
    request_token_counter = request_token_counter + 1
    token = 'u%d'%request_token_counter
    path = '/org/freedesktop/portal/desktop/request/%s/%s'%(sender_name, token)
    return (path, token)


def camera_call(method, callback, *args, options={}):
    (request_path, request_token) = new_request_path()
    bus.add_signal_receiver(handler_function=callback,
                            signal_name='Response',
                            dbus_interface=request_iface,
                            bus_name='org.freedesktop.portal.Desktop',
                            path=request_path)
    options['handle_token'] = request_token
    print('request token: %s, path: %s'%(request_token, request_path))
    return method(*(args + (options, )),
                  dbus_interface=camera_iface)


def open_pipewire_remote():
    global fd
    fd_object: dbus.UnixFd = portal.OpenPipeWireRemote({}, dbus_interface=camera_iface)
    fd = fd_object.take()


def on_access_camera_response(response, results) -> bool:
    global cam
    print(results)
    if response != 0:
        print("Failed to access: %s"%response)
        print(results)
        return False

    open_pipewire_remote()
    return True


def extract_frame(sample: Gst.Sample) -> np.ndarray:
    buffer = sample.get_buffer()

    caps_format = sample.get_caps().get_structure(0)

    video_format = GstVideo.VideoFormat.from_string(caps_format.get_value('format'))

    w, h = caps_format.get_value('width'), caps_format.get_value('height')
    c = gst_utils.get_num_channels(video_format)

    buffer_size = buffer.get_size()
    shape = (h, w, c) if (h * w * c == buffer_size) else (h, w, 3)
    array = np.ndarray(shape=shape, buffer=buffer.extract_dup(0, buffer_size), dtype=gst_utils.get_np_dtype(video_format))

    return np.squeeze(array)


def process_frame(sink: GstApp.AppSink, data: Any) -> Gst.FlowReturn:
    sample = sink.emit("pull-sample")
    if isinstance(sample, Gst.Sample):
        array = extract_frame(sample)

        writer.write(array)

        return Gst.FlowReturn.OK

    return Gst.FlowReturn.ERROR


if __name__ == '__main__':
    portal = bus.get_object('org.freedesktop.portal.Desktop',
                            '/org/freedesktop/portal/desktop')

    if not portal.IsCameraPresent:
        print("No camera available")

    camera_call(portal.AccessCamera, on_access_camera_response)

    with GstContext():
        for i in range(30, 0, -1):
            if fd is not None:
                break
            sleep(1)
        if i == 0:
            print('Timeout while waiting for portal!')
            exit(1)

        gst_command = f'pipewiresrc fd={fd} ' \
                      f'!  jpegdec ' \
                      f'! videoconvert ' \
                      f'! video/x-raw,format=BGR ' \
                      f'! queue ' \
                      f'! appsink emit-signals=True'

        with GstPipeline(gst_command) as pipeline:
            appsink = pipeline.get_by_cls(GstApp.AppSink)[0]
            appsink.connect("new-sample", process_frame, None)
            try:
                while not pipeline.is_done:
                    sleep(0.025)
            except KeyboardInterrupt:
                print("Shutting down gracefully")

        writer.close()

required system packages

# These are the package names as I needed them on Fedora 36
ffmpeg #(nonfree variant, see https://www.tecmint.com/install-ffmpeg-in-linux/)
pipewire
pipewire-gstreamer
pipewire-plugin-libcamera
gstreamer1
gstreamer1-plugins-base
gstreamer1-plugins-good
libcamera-gstreamer
pipewire-gstreamer
python3-gstreamer
libcamera

requirements.txt

gstreamer-python @ git+https://github.com/jackersson/gstreamer-python.git@c8d4e04e1cdeb3b284641b981afcf304f50480db
numpy
opencv-python==4.6.0.66
vidgear==0.2.6

@abhiTronix Yes, you're probably right. After struggling with pipewire for a few days, I think, it's just not ready yet (at least the video API in languages other than C). Ideally, pipewire would bring virtual video devices to userland, so that noone needs to setup and use v4l2loopback anymore - that's the biggest appeal I see in it. But for now, few programs are using pipewire nodes instead of v4l devices and there's no big benefit from supporting this.

However, xdg-desktop-portals are a different story. Devs are well-advised to use them for camera access (whether they are using pipewire or not), as that increases compatibility with containerized application (which are becoming the de-facto standard of linux package distribution).