So I was able to port the Novacut renderer to PyGI save for one problem I wasn't able to work around: the message bus is broken under PyGI and I'm not getting an EOS signal.  The render actually works fine, I just don't know when it's done.

I finally came of with two illustrative test cases, which hopefully will allow someone with more G-I knowledge to spot the problem.

Here is the working case for the static python-gst bindings:

#!/usr/bin/python

from gi.repository import GObject
GObject.threads_init()

from gi.repository import Gst
Gst.init(None)

mainloop = GObject.MainLoop()
pipeline = Gst.Pipeline()

def on_eos(bus, msg):
    print('eos: {!r}'.format(msg))
    pipeline.set_state(gst.STATE_NULL)
    mainloop.quit()

def on_message(bus, msg):
    print('message: {!r}'.format(msg))

bus = pipeline.get_bus()
bus.add_signal_watch()
bus.connect('message::eos', on_eos)
bus.connect('message', on_message)

bus = pipeline.get_bus()
bus.add_signal_watch()
bus.connect('message::eos', on_eos)

src = Gst.ElementFactory.make('videotestsrc', None)
src.set_property('num-buffers', 120)
sink = Gst.ElementFactory.make('fakesink', None)
pipeline.add(src)
pipeline.add(sink)
src.link(sink)

pipeline.set_state(Gst.State.PLAYING)
mainloop.run()


And here is the broken PyGI case:

#!/usr/bin/python

from gi.repository import GObject
GObject.threads_init()

from gi.repository import Gst
Gst.init(None)

mainloop = GObject.MainLoop()
pipeline = Gst.Pipeline()

def on_eos(bus, msg):
    print('eos: {!r}'.format(msg))
    pipeline.set_state(gst.STATE_NULL)
    mainloop.quit()

def on_message(bus, msg):
    print('message: {!r}'.format(msg))

bus = pipeline.get_bus()
bus.add_signal_watch()
bus.connect('message::eos', on_eos)
bus.connect('message', on_message)

bus = pipeline.get_bus()
bus.add_signal_watch()
bus.connect('message::eos', on_eos)

src = Gst.ElementFactory.make('videotestsrc', None)
src.set_property('num-buffers', 10)
sink = Gst.ElementFactory.make('fakesink', None)
pipeline.add(src)
pipeline.add(sink)
src.link(sink)

pipeline.set_state(Gst.State.PLAYING)
mainloop.run()


Here is the trace when I try to run the broken PyGI case:

jderose@jgd-ws:~/bzr/novacut/trunk$ ./eos-bug-pygi.py
./eos-bug-pygi.py:37: Warning: g_value_get_object: assertion `G_VALUE_HOLDS_OBJECT (value)' failed
  mainloop.run()
message: None
message: None
message: None
message: None
message: None
message: None
message: None
message: None
message: None
message: None
message: None
message: None
message: None
Traceback (most recent call last):

+ Trace 228660