FIX: QWheelEvent no longer has a delta()
WORKAROUND: For streams that don't publish an r_frame_rate

I am curious, though, what avg_frame_rate holds... I need to add that to
probe.

The real solution here is to build an index of the pts/dts of each frame.
Then I can seek to each frame with absolute accuracy.
Make average frame rate and metadata available from AVContainer

Quite honestly, I don't know the difference between average frame rate and
r_frame_rate. They seem to be present or absent together.
Want to see message boxes when something bad happens

Going to have to improve this quite a bit.