Python + QT + Gstreamer

Question

I'm working with PyQt and trying to get video from a webcam to play within a QT widget. I've found tutorials for C and Qt, and for python and gtk, but NOTHING for this combo of pyQt and gstreamer. Anybody get this working?

This plays the video fine, but in a separate window:

self.gcam = gst.parse_launch('v4l2src device=/dev/video0 ! autovideosink')
self.gcam.set_state(gst.STATE_PLAYING)

what I need is to get the overlay working so it's displayed within a widget on my GUI. Thanks, Gurus of the internet!

ok, so I've gotten a lot farther, but still in need of some help. I'm actually writing this for Maemo, but the following code works fine on my linux laptop:

class Vid:
    def __init__(self, windowId):
    self.player = gst.Pipeline("player")
    self.source = gst.element_factory_make("v4l2src", "vsource")
    self.sink = gst.element_factory_make("autovideosink", "outsink")
    self.source.set_property("device", "/dev/video0")
    self.scaler = gst.element_factory_make("videoscale", "vscale")
    self.window_id = None
    self.windowId = windowId

    self.player.add(self.source, self.scaler, self.sink)
    gst.element_link_many(self.source,self.scaler, self.sink)

    bus = self.player.get_bus()
    bus.add_signal_watch()
    bus.enable_sync_message_emission()
    bus.connect("message", self.on_message)
    bus.connect("sync-message::element", self.on_sync_message)

    def on_message(self, bus, message):
    t = message.type
    if t == gst.MESSAGE_EOS:
        self.player.set_state(gst.STATE_NULL)
    elif t == gst.MESSAGE_ERROR:
       err, debug = message.parse_error()
       print "Error: %s" % err, debug
       self.player.set_state(gst.STATE_NULL)

    def on_sync_message(self, bus, message):
    if message.structure is None:
        return
    message_name = message.structure.get_name()
    if message_name == "prepare-xwindow-id":
        win_id = self.windowId
        assert win_id
        imagesink = message.src
        imagesink.set_property("force-aspect-ratio", True)
        imagesink.set_xwindow_id(win_id)
    def startPrev(self):
    self.player.set_state(gst.STATE_PLAYING)
    print "should be playing"
vidStream = Vid(wId)
vidStream.startPrev()

where wId is the window id of the widget im trying to get to display the output in. When I run this on the N900, the screen goes black and blinks. Any ideas? I'm dying here!

EDIT: I've been asked to post the full code, and though I still need to clean it up a bit, here's the relevant part:

self.cameraWindow = QtGui.QWidget(self)
self.cameraWindow.setGeometry(QtCore.QRect(530, 20, 256, 192))
self.cameraWindow.setObjectName("cameraWindow")
self.cameraWindow.setAttribute(0, 1); # AA_ImmediateWidgetCreation == 0
self.cameraWindow.setAttribute(3, 1); # AA_NativeWindow == 3

global wId
wId = self.cameraWindow.winId()

self.camera = Vid(wId)

self.camera.startPrev()

class Vid:
    def __init__(self, windowId):
    self.player = gst.Pipeline("player")
    self.source = gst.element_factory_make("v4l2src", "vsource")
    self.sink = gst.element_factory_make("autovideosink", "outsink")
    self.source.set_property("device", "/dev/video0")
    #self.scaler = gst.element_factory_make("videoscale", "vscale")
    self.fvidscale = gst.element_factory_make("videoscale", "fvidscale")
    self.fvidscale_cap = gst.element_factory_make("capsfilter", "fvidscale_cap")
    self.fvidscale_cap.set_property('caps', gst.caps_from_string('video/x-raw-yuv, width=256, height=192'))
    self.window_id = None
    self.windowId = windowId
    print windowId

    self.player.add(self.source, self.fvidscale, self.fvidscale_cap, self.sink)
    gst.element_link_many(self.source,self.fvidscale, self.fvidscale_cap, self.sink)

    bus = self.player.get_bus()
    bus.add_signal_watch()
    bus.enable_sync_message_emission()
    bus.connect("message", self.on_message)
    bus.connect("sync-message::element", self.on_sync_message)

    def on_message(self, bus, message):
    t = message.type
    if t == gst.MESSAGE_EOS:
        self.player.set_state(gst.STATE_NULL)
    elif t == gst.MESSAGE_ERROR:
       err, debug = message.parse_error()
       print "Error: %s" % err, debug
       self.player.set_state(gst.STATE_NULL)

    def on_sync_message(self, bus, message):
    if message.structure is None:
        return
    message_name = message.structure.get_name()
    if message_name == "prepare-xwindow-id":
        win_id = self.windowId
        assert win_id
        imagesink = message.src
        imagesink.set_property("force-aspect-ratio", True)
        imagesink.set_xwindow_id(win_id)
    def startPrev(self):
    self.player.set_state(gst.STATE_PLAYING)
    def pausePrev(self):
    self.player.set_state(gst.STATE_NULL)

This is piecing together a few bits, and I can't test it right now, but maybe it will be helpful to someone. Good luck!

Answer 1

If you're happening to use PySide instead of PyQt on a platform other than Linux, winId() returns a PyCObject which can't be used directly with native functions or other modules. In my case this came in handy when using GStreamer (pygst) with PySide on Microsoft Windows:

from ctypes import pythonapi, c_void_p, py_object
...
if message_name == 'prepare-xwindow-id':
    # convert winId from PyCObject to void pointer
    pythonapi.PyCObject_AsVoidPtr.restype = c_void_p
    pythonapi.PyCObject_AsVoidPtr.argtypes = [py_object]
    hWnd = pythonapi.PyCObject_AsVoidPtr(self.videoWidget.winId())

    # set window handle to video sink
    self.videoSink.set_xwindow_id(hWnd)