Video wait spinner may flicker in and out

[Wumpf]

Whenever the decoder just barely can't keep up, the wait spinner flickers in and out of existence a lot which can be rather irritating.
We need to find a better way to visualize that the image on screen is not exactly up to date and show large animations like the loading spinner only for reasonably long waits.

This is easiest reproed with high resolution & framerate material at increased playback speed, or just by using a slower computer or decoder.

Related(ish):

• Spinner shows when reaching end of video #7570
• Web video decoder can get stuck on high load #7582