Record opengl content from QWidget in a thread - multithreading

Question

I use some software (Nuke) with GUI in PySide and I would to grab the content of a QGLWidget recognized in QWidget by PySide (weird) and encode it to video.
So, I can't use QGLWidget.grabFrameBuffer():
AttributeError: 'PySide.QtGui.QWidget' object has no attribute 'grabFrameBuffer'
I tried:
# Qwidget.render(QImage)
image = QtGui.QImage(child.width(),child.height(),QtGui.QImage.Format_RGB32)
child.render(image)
image.save( '/Volumes/LaCie_Work/_TMP/test/test0.png', 'PNG')
Result : http://i.imgur.com/YwTtR2q.png - Problem : Miss lot of elements
# Qwidget.render(QPixmap)
image = QtGui.QPixmap(child.size())
child.render(image)
image.save( '/Volumes/LaCie_Work/_TMP/test/test1.png', 'PNG')
Result : http://i.imgur.com/DqO1PBS.png - Problem : No ! (see further below)
# QPixmap.grabWidget(QWidget)
image = QtGui.QPixmap.grabWidget(child)
image.save( '/Volumes/LaCie_Work/_TMP/test/test2.png', 'PNG')
Result : http://i.imgur.com/9n9Hofy.png - Problem : Not exactly but ok.. (see further below)
# QPixmap.grabWindow(QWidget.winId())
image = QtGui.QPixmap.grabWindow(child.winId())
image.save( '/Volumes/LaCie_Work/_TMP/test/test2.png', 'PNG')
Result : http://i.imgur.com/ewwDdZW.png - Problem : WTF ?!
All these methods are "threadable", BUT in a thread or not, if I create a simple sphere (or whatever) in this viewport the software (Nuke again) crash. I don't know why...
I decided to try with pyOpenGl:
# pyOpenGl glReadPixel
buffer = glReadPixels(0, 0, child.width(), child.height(), GL_RGB, GL_UNSIGNED_BYTE)
image = PIL.Image.fromstring(mode="RGB", size=(child.width(),child.height()), data=buffer)
image = image.transpose(PIL.Image.FLIP_TOP_BOTTOM)
image.save( '/Volumes/LaCie_Work/_TMP/test/test.png', 'PNG')
Result : http://i.imgur.com/7oBEAgj.png - Problem : Any !! :)
But...
glReadPixels need to be called in the main thread to get the right context and that hang the software... (12 to 24 frames per second) :(
With Qt :
1) Why my QGLWidget is recognize like QWidget ? (pyside bug ?)
2) Here is a way to force grabFrameBuffer() ?
3) Can I live stream the QWidget content to a QGLWidget and grab it ?
With PyOpenGL :
4) Could I access a specific Qwidget Framebuffer from a thread ?
5) Bind the FBO in an other in a new thread ?
Any help or suggestion is very welcome!