callbacks in Mac video player?

[Richard Gaskin]

The Dictionary says callbacks still work on macOS, but it also says 
they're supported on Linux, where I don't recall callbacks ever being 
supported, and for several years video playback doesn't work at all.

I can't make callbacks work on macOS Catalina using v9.5.

Should they?

-- 
  Richard Gaskin
  Fourth World Systems
  Software Design and Development for the Desktop, Mobile, and the Web
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