Fix unexpected stop of media playback via ffmpeg proxy for ESPhome devices

[mib1185]

Proposed change

The ffmpeg tool writes per default its progress stats to stderr. These stats reaches after ~ 30min already 2750 entries with each 70 bytes.
The stderr is connected to a subprocess pipe, but never read, so the buffer to be overflowed, so that the task get canceled. Further the stderr is only read in case of an error, so no need to write the progress stats into it.

source: https://ffmpeg.org/ffmpeg.html#Main-options

-stats (global)
Log encoding progress/statistics as "info"-level log (see -loglevel). It is on by default, to explicitly disable it you need to > specify -nostats.

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[home-assistant]

Hey there @OttoWinter, @jesserockz, @kbx81, @bdraco, mind taking a look at this pull request as it has been labeled with an integration (esphome) you are listed as a code owner for? Thanks!

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[bdraco]

Should we connect stderr to dev null or log it somewhere ?

[mib1185]

I've thought about devnull, but it is read in case of any other errors:

core/homeassistant/components/esphome/ffmpeg_proxy.py

Lines 235 to 238 in aadb43c

	stderr_text = ""
	while line := await proc.stderr.readline():
	stderr_text += line.decode()
	_LOGGER.error("FFmpeg output: %s", stderr_text)

I don't think, we need to log it - at most as a debug log maybe 🤔

[bdraco]

I think this is fine for a patch release.

We might want to change it to https://docs.python.org/3/library/asyncio-subprocess.html#asyncio.subprocess.Process.communicate in the future so it does log stderr if something does go wrong later in the process.

[marcelveldt]

stderr pipe might still fill up if there are errors being logged by ffmpeg, which can happen very quickly in case of encoding issues. I think a better future-proof approach will be to keep reading stderr in a separate task to avoid the deadlock situation.

[mib1185]

done in #130808