Mysterious segfault using PyGTK and PyGST, runs as intended in gdb

Question

I'm trying to write a proof-of-concept python program to display a video (using gstreamer) in a pyGTK DrawingArea object, with the end goal of a screensaver-like behavior that runs the video in a loop and exits on mouse activity.

However when I succeeded in connecting the gstreamer output to the X window created by pygtk I got a segfault. running it in GDB however works generally as intended (not full screen but I'd imagine that's a separate issue) And to make things even more interesting if I run it in gdb, my next run outside of gdb will succeed as well, but then fail thereafter.

This is the code I'm using: (python 2.7)

#!/usr/bin/env python
import pygst
pygst.require("0.10")
import gst
import time
import pygtk
pygtk.require('2.0')
import gtk

class VideoPlayer:

  def on_new_decoded_pad(self, dbin, pad):
    self.demux.link(self.h264)
    #self.pipeline.set_state(gst.STATE_PLAYING)
    print "linked!"

  def varea_realized(self, varea):
    print "varea realized"
    self.varea.window.fullscreen()
    self.sink.set_xwindow_id(self.varea.window.xid)
    self.pipeline.set_state(gst.STATE_PLAYING)

  def __init__(self):
    self.win = gtk.Window(gtk.WINDOW_TOPLEVEL)
    self.varea = gtk.DrawingArea()
    self.win.fullscreen()

    self.win.add(self.varea)

    self.varea.connect('realize', self.varea_realized)

    self.pipeline = gst.Pipeline("mypipe")
    self.src = gst.element_factory_make("filesrc", "src")
    self.src.set_property('location', '/home/myuser/TestMpeg4.mp4')
    self.demux = gst.element_factory_make("qtdemux", "demux")
    self.h264 = gst.element_factory_make("ffdec_h264", "h264")
    self.crop = gst.element_factory_make("videocrop", "crop")
    self.crop.set_property('left', 125)
    self.crop.set_property('right', 125)
    self.scale = gst.element_factory_make("videoscale", "scale")
    self.cap = gst.Caps("video/x-raw-yuv,width=1024,height=1280")
    self.capFilter = gst.element_factory_make("capsfilter")
    self.capFilter.props.caps = self.cap
    self.sink = gst.element_factory_make("xvimagesink", "sink")
    self.pipeline.add_many(self.src, self.demux, self.h264, self.sink, self.scale, self.capFilter, self.crop)

    gst.element_link_many(self.src, self.demux)
    gst.element_link_many(self.h264, self.crop, self.scale, self.capFilter, self.sink)
    self.demux.connect("pad-added", self.on_new_decoded_pad)
    self.pipeline.set_state(gst.STATE_PAUSED)
    #win.realize()
    self.win.show_all()
    #sink.set_xwindow_id(win.window.xid)
    #demux.link(h264)
    #h264.link(sink)
    self.pipeline.set_state(gst.STATE_PLAYING)


if __name__ == "__main__":
  VideoPlayer()
  gtk.main()

And when I run it via the command line:

user@kiosk:~$ ./vidtest.py
varea realized
Segmentation fault (core dumped)

whereas in gdb:

user@kiosk:~$ gdb python
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /usr/bin/python...Reading symbols from /usr/lib/debug/usr/bin/python2.7...done.
done.
(gdb) run vidtest.py
Starting program: /usr/bin/python vidtest.py
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7ffff7ffa000
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffe6dc9700 (LWP 740)]
[New Thread 0x7fffe65c8700 (LWP 741)]
varea realized
Traceback (most recent call last):
  File "vidtest.py", line 13, in on_new_decoded_pad
    self.demux.link(self.h264)
gst.LinkError: failed to link demux with h264
linked!
[New Thread 0x7fffe4aba700 (LWP 742)]
[Thread 0x7fffe4aba700 (LWP 742) exited]
^C
Program received signal SIGINT, Interrupt.
0x00007ffff6990d83 in poll () from /lib/x86_64-linux-gnu/libc.so.6
(gdb)

I'm not worried about the failed link (that's the audio track which I don't need, although I'll have to handle it eventually) but the program runs correctly and is then terminated with a Ctrl-C

I did run strace on it successfully and found the segfault was happening right around here:

user@kiosk:~$ strace ./vidtest.py
<Omitted for brevity...>
open("/home/user/TestMpeg4.mp4", O_RDONLY) = 6
fstat(6, {st_mode=S_IFREG|0664, st_size=10947268, ...}) = 0
lseek(6, 0, SEEK_END)                   = 10947268
lseek(6, 0, SEEK_SET)                   = 0
fstat(6, {st_mode=S_IFREG|0664, st_size=10947268, ...}) = 0
write(5, "\1\0\0\0\0\0\0\0", 8)         = 8
mmap(NULL, 8392704, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7f4afe20e000
mprotect(0x7f4afe20e000, 4096, PROT_NONE) = 0
clone(child_stack=0x7f4afea0dff0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7f4afea0e9d0, tls=0x7f4afea0e700, child_tidptr=0x7f4afea0e9d0) = 863
futex(0x184a9b0, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x118fed0, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x1851900, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x1758500, FUTEX_WAKE_PRIVATE, 1) = 1
write(5, "\1\0\0\0\0\0\0\0", 8)         = 8
write(5, "\1\0\0\0\0\0\0\0", 8)         = 8
uname({sys="Linux", node="kiosk", ...}) = 0
fstat(1,  <unfinished ...>
+++ killed by SIGSEGV (core dumped) +++
Segmentation fault (core dumped)
user@kiosk:~$

Any clue as to what may be going on (given it's a segfault I assume some sort of memory issue in either pygst or pygtk, but I'm not sure what I did to cause it) or more debugging steps to try would be greatly appreciated.