Home Assistant Core 2025.12.x forces TTS audio files to be generated in FLAC format, completely ignoring the preferred_format settings. The Voice Preview Edition speakers cannot successfully receive FLAC files through the ffmpeg_proxy service, resulting in silent playback timeouts.
I tried downgrading but ended up with db issues, so back to the new version for now and living with the silent speakers.
Also see: ## Voice PE FLAC Playback Timeout - HA 2025.12 Regression