Posibility to add advanced settings for Video

[mateosalta]

Add sliders for "Brightness", "Contrast" maybe as advanced settings somewhere.

xvimagesink http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-plugins/html/gst-plugins-base-plugins-xvimagesink.html#gst-plugins-base-plugins-xvimagesink.synopsis works for this and I can allready hack in values in around say:

def on_sync_message(self, bus, msg):
if msg.get_structure().get_name() == 'prepare-window-handle':
print('prepare-window-handle')
msg.src.set_property('force-aspect-ratio', True)
msg.src.set_property('brightness', -200)
msg.src.set_property('contrast', 200)
print('prepped')

possibly hue and saturation (mine the auto color goes a bit off, would be nice for white balance) or Special effects!