Wires --whisper flag in converse_server using the existing whisper-rs
asr feature. AsrEngine enum (Kyutai default + Whisper variant gated on
"asr" feature) lets the receive loop branch on backend. Whisper path:
buffer audio during receive, transcribe full buffer at EOT — batch-only,
no VAD, no incremental words.
Adds examples/whisper_profile binary measuring Whisper-tiny in
isolation against the same audio used for stt_profile.
Standalone profile findings (M-series):
Kyutai STT 1B : 80.8 ms / 80 ms audio 1.01x realtime
Whisper-tiny : 209 ms / 10.43 s audio 0.020x (~50x faster)
But the full-stack bench reveals a critical regression: linking
whisper-rs's C++ runtime into the same binary as candle/CSM costs
2-3x across ALL CSM inference (recv_phase, tts_per_utterance,
total_turn) even when --whisper is NOT used. Build flag matters.
Build recv tts/u total
--features metal 4196 3113 18707
--features metal,asr (Kyutai) 10019 7803 43366 <- linkage cost
--features metal,asr +whisper 0 12921 54028 <- worse
Suspected cause: ggml/whisper.cpp's BLAS or Metal context init
conflicts with candle's. Production verdict: build WITHOUT asr
feature; accept Kyutai's 1x realtime STT cost. The standalone
whisper_profile binary still works for batch transcribe measurement.
Real Whisper integration would need a sidecar process pattern (whisper
running as a separate binary, IPC to converse_server). Documented in
the --whisper CLI help. Flag stays as opt-in with explicit warning.
Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
