Prevent ffmpeg from hanging extracting subtitles (#17297)

* Prevent ffmpeg from hanging extracting subtitles
Add `RunSubtitleExtractionProcess` to unify the external
_ffmpeg_ process handling and error management.
Add a `-nostdin` flag that prevents _ffmpeg_ from reading from
_stdin_ and blocking on an inherited stdin handle (e.g. when
Jellyfin runs as a service under NSSM), which otherwise hangs
subtitle extraction forever when _ffmpeg_ blocks on any
keyboard-interaction read until the timeout (30 minutes).
Close the redirected _stdin_ to ensure immediage EOF.
Drain the _stderr_ to a string and log it, to ensure we don't block
the _ffmpeg_ process on errors that exceed the pipe length.
Pass `-y` to _ffmpeg_ to ensure it overwrites any existing output file
without prompting for confirmation.

* Address review comments
Make sure we always drain stderr.
Make sure the timeout also honors the cancellationToken.
Make sure when we get cancelled we don't log it as a ffmpeg error.

0 files changed, 0 insertions, 0 deletions