WhisperX transcription called `whisperx.load_audio()`, which shells out to a
literal `"ffmpeg"` resolved against the OS PATH. On Windows that resolves to a
WindowsApps alias stub or a corrupt/wrong-arch binary — passing `which` but
exploding at spawn with `[WinError 193] %1 is not a valid Win32 application`.
whisperx only catches `CalledProcessError`, so the spawn-time `OSError` escaped
and the dub/batch path reported the opaque "Transcription produced no segments".
#377 added ffmpeg validation but only for the dub-export path; the transcription
path never went through the validated resolver. Since WhisperX is a default ASR
engine, this is a P0 platform-parity break (works on mac/Linux, fails on Windows).
Fix: decode the audio ourselves in `WhisperXBackend.transcribe` via
`find_ffmpeg()` (which `-version`-probes each candidate and returns the bundled
imageio-ffmpeg / Tauri sidecar) and hand WhisperX the array — bypassing the bare
PATH lookup entirely. This is more robust than a PATH-prepend, which couldn't
fix the imageio case (its binary is named `ffmpeg-<plat>-vN.exe`, not `ffmpeg`).
If no runnable ffmpeg exists, raise a clear, locale-independent error instead of
"no segments". Fixes both the dub and batch transcription paths.
Co-authored-by: mergetest <test@local>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
