Re-encode audio to AAC for non-local outputs.

[j0sh]

Output audio is in Opus for WebRTC, but re-encode to AAC for non-local RTMP outputs (studio, youtube, etc) because not everyone supports Opus-in-RTMP.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 31.70303%. Comparing base (808f793) to head (ab18dee).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
server/ai_live_video.go	0.00000%	5 Missing ⚠️
server/ai_mediaserver.go	0.00000%	3 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3657         +/-   ##
===================================================
- Coverage   31.70561%   31.70303%   -0.00258%     
===================================================
  Files            156         156                 
  Lines          47244       47251          +7     
===================================================
+ Hits           14979       14980          +1     
- Misses         31382       31388          +6     
  Partials         883         883                 

Files with missing lines	Coverage Δ
server/ai_process.go	1.68067% <ø> (ø)
server/ai_mediaserver.go	4.71888% <0.00000%> (-0.01425%)	⬇️
server/ai_live_video.go	0.00000% <0.00000%> (ø)

... and 1 file with indirect coverage changes

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Files with missing lines	Coverage Δ
server/ai_process.go	1.68067% <ø> (ø)
server/ai_mediaserver.go	4.71888% <0.00000%> (-0.01425%)	⬇️
server/ai_live_video.go	0.00000% <0.00000%> (ø)

... and 1 file with indirect coverage changes

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