ai/live: Cancel ffmpeg exec when segmenter exits.

[j0sh]

This prevents ffmpeg from reading indefinitely when there is no segment handling attached. That in turn can lead to disk filling up since ffmpeg writes segments to disk without removing them.

Also use context logging for some segmenter error messages.

Couldn't quite reproduce the buggy behavior we see in prod in order to completely verify this fix locally but I think this should be close enough for some cases.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 33.71714%. Comparing base (3e94431) to head (4fb7691).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
media/rtmp2segment.go	0.00000%	7 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3367         +/-   ##
===================================================
- Coverage   33.71894%   33.71714%   -0.00180%     
===================================================
  Files            141         141                 
  Lines          37430       37432          +2     
===================================================
  Hits           12621       12621                 
- Misses         24088       24090          +2     
  Partials         721         721                 

Files with missing lines	Coverage Δ
media/rtmp2segment.go	0.00000% <0.00000%> (ø)

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Files with missing lines	Coverage Δ
media/rtmp2segment.go	0.00000% <0.00000%> (ø)