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Providers

ASR backends implement TranscriptionProvider. Cleanup is a separate stage (see Cleanup).

Local (default)
Engine whisper.cpp via whisper-rs
Auth None
GPU Metal on macOS builds
Models ggml catalogue — aurum models
Context Process-level cache; call clear_context_cache() before exit in long-lived hosts
Integrity Magic check + pinned SHA-256 for common models 
aurum talk.m4a --model tiny-q5_1
aurum talk.m4a --model base

OpenRouter
Auth OPENROUTER_API_KEY (preferred) or config
Paths Dedicated /audio/transcriptions or multimodal chat (input_audio)
Mode --openrouter-stt-mode auto\|chat\|transcriptions (default auto)
SRT Only when the route reports reliable timestamps (dedicated ASR)

Capability-authoritative auto routing

auto does not guess from model-name substrings. It only routes models present in the reviewed static registry (OPENROUTER_STT_REGISTRY in aurum-core). Unknown model ids fail closed with an explicit error — set --openrouter-stt-mode chat or transcriptions yourself for unlisted models.

Registry class HTTP path backend_kind Timestamps
Dedicated ASR (e.g. openai/whisper-large-v3, openai/gpt-4o-transcribe) /audio/transcriptions asr reliable
Multimodal chat (e.g. google/gemini-2.5-flash) /chat/completions llm_assisted unreliable 
export OPENROUTER_API_KEY=sk-or-...
# Registered multimodal chat model (auto → chat)
aurum talk.mp3 --provider openrouter --model google/gemini-2.5-flash
# Registered dedicated ASR (auto → transcriptions)
aurum talk.mp3 --provider openrouter --model openai/whisper-large-v3 -o srt
# Unregistered model: must choose a path explicitly
aurum talk.mp3 --provider openrouter --model vendor/custom-audio \
  --openrouter-stt-mode chat -o json

Privacy settings

OpenRouter account privacy/guardrails must allow the chosen provider, or you will see No endpoints available matching your guardrail restrictions. Configure at https://openrouter.ai/settings/privacy

flowchart TB
  subgraph local [local]
    A[PCM 16 kHz mono] --> B[WhisperContext cache]
    B --> C[segments + text]
  end
  subgraph remote [openrouter]
    D[encode upload] --> R{auto registry}
    R -->|ASR record| E1[/audio/transcriptions]
    R -->|chat record| E2[/chat/completions]
    R -->|unknown| X[fail closed]
    E1 --> F[text + timestamps]
    E2 --> G[text LLM-assisted]
  end