## The symptom
Batch transcription with the `DiarizationEnabled` property set produces
transcription JSON with no `Speaker` property at all. The flag looks ignored.
Multiple audio files, including ones with clearly distinct male and female
voices, all come back with no speaker labels.
## Why
From the service logs: the input file was stereo, and for stereo files
diarization is not possible, so the service silently ignored the diarization
flag. The silent ignore was a bug on the service side; a fix was being deployed
to return a clear error message instead of doing nothing. But the underlying
constraint remains.
## The fix
Downmix your audio to mono before submitting the transcription request. The
`Speaker` property then shows up in the results.
1. Check your input: `ffprobe` will tell you the channel count.
2. If stereo, downmix: `ffmpeg -i input.wav -ac 1 mono.wav` (or do it in your
audio pipeline).
3. Resubmit the mono file with `DiarizationEnabled` set.
## Watch out
This failure mode gives you no error, just missing data, which makes it look
like the feature is broken. If diarization returns nothing on any file, check
the channel count before anything else.