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Audio Transcription Service (M17-Whisper)

Audio transcription service for DIDI media analysis. Whisper-based (M17-Whisper, faster-whisper backend), used by agent-v3 media-preprocess worker for video/audio session pipelines (techniques, ai-tampered, claims). OpenAI-compatible API — drop-in for client.audio.transcriptions.create().

Stack

  • Python 3.10+ / FastAPI / Uvicorn
  • Backend: faster-whisper >= 1.0.0 (CTranslate2 optimized inference)
  • Default model: large-v3-turbo (809M params, ~6GB VRAM int8)
  • GPU: CUDA (shared GPU 0 with Qwen3.5-35B-A3B)
  • URL (Dev): http://10.11.10.17:54300/v1/audio/transcriptions
  • Container: didiAI-audio (GPU host)
  • Auth: none on the service itself; agent-v3 uses bearer token via M17_WHISPER_TOKEN (enforced by gateway/nginx if configured)

Ce face

Speech-to-text transcription pe fişiere audio sau URL-uri. agent-v3 trimite fie audio buffer (multipart upload), fie URL public (din MinIO), primeşte text + metadata (lang detect, duration, optional segments). Folosit în:

  • Video analysis pipeline — agent-v3 extrage track-ul audio cu ffmpeg, trimite la M17-Whisper, foloseşte transcript pentru claims + techniques + ai-tampered
  • Audio-only sessions — direct upload, transcripted, apoi pipeline normal de analiză text
  • Cascade fallback — agent-v3 transcription.ts are cascadă: M17-Whisper (local GPU) → Groq Whisper → OpenAI Whisper. Dacă local pică sau întoarce string gol, trece la următorul provider.

API endpoints

Method Path Purpose
GET /health Health probe (returns {"status":"ok"})
GET /v1/models List models, OpenAI-compatible
POST /v1/audio/transcriptions Transcribe audio (OpenAI-compatible)
GET /v1/info Service catalog metadata (used by didi catalog-api)

POST /v1/audio/transcriptions

Content-Type: multipart/form-data

Param Type Default Notes
file file — Audio file (MP3/WAV/M4A/FLAC/OGG/MP4 audio track…). XOR with url.
url string — URL to download audio from (DIDI extension over OpenAI). XOR with file.
model string configured Ignored — server uses AUDIO_MODEL env.
language string auto ISO-639-1 code (en, ro, es, …). Auto-detect if omitted.
prompt string none Optional initial prompt to bias style/vocab.
response_format string json json | text | verbose_json (segments).
temperature float 0.0 Sampling temperature 0.0–1.0.

Response (json): { text, language, duration } — verbose_json adds segments[] with start/end/text/tokens/avg_logprob/no_speech_prob.

Errors: 400 invalid params / download failed, 413 payload too large (default 500MB), 422 corrupted audio, 500 transcription failed, 503 model not loaded.

Backends / Models

  • Production: large-v3-turbo (8x faster than large-v3, similar quality, ~6GB VRAM int8)
  • Available: tiny, base, small, medium, large-v3, large-v3-turbo
  • VAD (Voice Activity Detection) enabled by default — skip silence
  • Quantization: int8 (recommended), float16, int8_float16

How didi-backend uses it

  • agent-v3 cascade: backend/services/orchestration-layer/agent-v3/src/shared/media/transcription.ts
    • Order: M17-Whisper (local GPU) → Groq Whisper → OpenAI Whisper
    • Empty-string from local triggers retry on next provider (Faza 1 din SAFETY_NETS_PLAN)
  • Configured în agent-v3 docker-compose env:
    • M17_WHISPER_URL=http://10.11.10.17:54300
    • M17_WHISPER_TOKEN=<gateway-token> (optional, dacă există proxy auth)
  • Apelat din media-preprocess worker la sesiuni cu media_type în {audio, video} — transcript devine input pentru claims-routes.ts, routes.ts (techniques), ai-tampered-routes.ts.
  • Video flow: ffmpeg extract → upload temp / pass buffer → POST /v1/audio/transcriptions → text → pipeline analysis.

Configuration

Env vars (prefix AUDIO_, set in deploy/.env):

Required

  • AUDIO_MODEL — Whisper model (default large-v3-turbo)
  • AUDIO_DEVICE — cuda | cpu
  • AUDIO_CACHE_DIR — HuggingFace model cache path (/cai2_ds_storage/hf_cache typical)
  • AUDIO_EXTERNAL_URL — used in OpenAPI servers spec

Optional

  • AUDIO_COMPUTE_TYPE — int8 (default), float16, int8_float16
  • AUDIO_BEAM_SIZE — beam search width (default 5)
  • AUDIO_BEST_OF — sampling candidates (default 5)
  • AUDIO_TEMPERATURE — default 0.0
  • AUDIO_HOST / AUDIO_PORT — default 0.0.0.0:54300
  • AUDIO_LOG_LEVEL — default INFO
  • AUDIO_MAX_FILE_SIZE_MB — upload cap (default 500)
  • CUDA_VISIBLE_DEVICES=0 — pinned to GPU 0

Deployment

Compose dir: /home/admin365/didi_mono/ai_platform/modules/audio/deploy/

cd modules/audio/deploy
cp ../.env.example .env   # edit values
./deploy.sh --profile api --detach          # API only
./deploy.sh --profile api-nginx --detach    # with nginx reverse proxy
./deploy.sh --profile api --logs            # tail logs
docker compose restart audio-api            # quick restart
  • Container name: didiAI-audio
  • Image: didiai-audio:audit
  • Network: didi-network (external, shared with other AI modules)
  • GPU reservation: NVIDIA driver, device 0
  • Healthcheck: HTTP GET /health every 30s, 60s start period (model load)
  • Model cache mount: ${AUDIO_CACHE_DIR}:/root/.cache/huggingface

Performance

  • Real-Time Factor on H200 GPU + int8 + large-v3-turbo: ~0.05–0.08x (10s audio = 0.5–1s transcription, 1h audio = 3–5min)
  • VRAM: ~6GB for large-v3-turbo int8, ~8GB float16
  • Throughput: sequential — process files one at a time per GPU
  • File size cap: 500MB default (configurable)
  • Recommended: pre-split audio > 1h cu ffmpeg segments

Architecture (source layout)

modules/audio/
├── deploy/
│   ├── deploy.sh                # CLI wrapper
│   ├── docker-compose.yml       # didiAI-audio service
│   ├── Dockerfile               # CUDA + faster-whisper image
│   └── .env                     # runtime config
├── src/audio/
│   ├── app.py                   # FastAPI routes + /v1/info catalog
│   ├── transcriber.py           # faster-whisper wrapper (singleton)
│   ├── schemas.py               # TranscriptionResponse / Segment
│   └── settings.py              # pydantic-settings (AUDIO_* env)
├── tests/
├── pyproject.toml               # fastapi, faster-whisper, httpx
├── README.md                    # full operator guide
├── API.md                       # full HTTP API reference
└── INDEX.md                     # this file

Related

  • agent-v3 transcription cascade — backend/services/orchestration-layer/agent-v3/src/shared/media/transcription.ts
  • agent-v3 media routes — routes.ts / ai-tampered-routes.ts / claims-routes.ts
  • media-preprocess worker (in agent-v3) — invokes this service
  • Test files in MinIO (used during refactor verification):
    • Audio: https://didi365.eu/api/v3/media/file/uploads/test-user/1771883851173-audio_with_voice.mp3
    • Video: https://didi365.eu/api/v3/media/file/uploads/test-user/1771883852186-voice_video.mp4
  • Faza 1 safety net (transcription retry on empty) — agent-v3/SAFETY_NETS_PLAN.md
  • Upstream refs: faster-whisper, OpenAI Whisper