Get parameter defaults from frei0r.
Merge pull request #27 from j-b-m/master

Fix crash in Kdenlive title producer (kdenlive-2987)
QApplication::processEvents is not needed in qglsl.
Some minor logging cleanup.
Cleanup the OpenGL context when consumer stops.
Fix OpenGL context cleanup on Windows.

Would crash at end of melt with qglsl.
Fix crash on missing NULL at end of mlt_events_fire().
Fix assert in libavformat using force_fps with AVI (kdenlive-2963).
Let movit.convert suport non-glsl to glsl_texture.

It saves the rendered texture and returns it.
Let qglsl multi consumer work with more consumers.

Works with sdl and decklink consumers.
Add new avsync module
Add mlt_service_filter_count and Mlt::Service::filter_count.
Show the invalid format in the error message.
Make opengl filters support attach, detach, and disable.
Add locking to opengl services for thread protection.
Cache the Movit chain used for RAM->GL texture conversion.
Improve refresh handling for sdl_audio consumer.

This may eventually be applied as well to sdl_preview.
Fix typo in logic
Let the app set a flag to get existing GL texture.
Fix type in movit.sharpen metadata.