Save webcam snapshot to file

Question

When I run this, I get the cam snapshot on the file:

gst-launch-0.10 v4l2src num-buffers=1 ! jpegenc ! filesink location=pic.jpg

I tried to put that in Python and instead of the pic I get an empty file. Can someone tell where the mistake is? It's a very simple code that should do a very simple task. Also, I don't want to use gst.parse_launch(), I need to understand the construction of pipelines in Python.

import sys, os
import pygtk, gtk, gobject
import pygst
pygst.require("0.10")
import gst


class GTK_Main:

    def __init__(self):


        self.player = gst.Pipeline("player")

        source = gst.element_factory_make("v4l2src", "video-source")
        source.set_property("num-buffers", 1)

        conv = gst.element_factory_make("jpegenc", "jpeg-converter")

        sink = gst.element_factory_make("filesink", None)
        sink.set_property("location", "pic.jpg")

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

        self.player.set_state(gst.STATE_PLAYING)

GTK_Main()
gtk.gdk.threads_init()