[mythtv] Audio-upmixing questions regarding #5900

[Yeechang Lee]

I've patched my 0.21-fixes setup with #5900, and am pleased that now
5.1 audio works when timestretching, as well as fixing some other
issues.

Three questions:

* Is 5.1 audio always upmixed, or is it passed through by default
  unless there's timeshifting?
* If the answer to the previous question is "Passed through," does
  upmixing automatically stop and the frontend revert to the native
  audio track if a 5.1 recording's timestretch is returned to 1.0X?
* What advantages/disadvantages, if any, are there to upmixing non-5.1
  audio to 5.1?

-- 
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