Assembly Ai

AssemblyAI is among the most capable and developer-friendly speech-to-text APIs available — high accuracy on real-world audio (meetings, calls, podcasts), clean async model for file transcription, and a growing suite of audio intelligence features (speaker diarization, sentiment analysis, entity detection, PII redaction, auto chapters, topic detection). For agents: submit an audio file URL, receive a transcript ID, poll or webhook when complete, parse the structured result. Real-time streaming available via WebSocket for live audio processing. Strong SDKs (Python, Node.js, Go, Ruby, Java) make integration fast. Free tier ($50 credit, no card) adequate for development. Confidence is docs-derived.

REST API at api.assemblyai.com/v2. Resources: transcript, upload, realtime. POST /v2/transcript submits a transcription job ({audio_url, speaker_labels, sentiment_analysis, entity_detection, iab_categories, redact_pii, auto_chapters, summarization, ...}). GET /v2/transcript/{id} polls transcript status (queued → processing → completed/error). DELETE /v2/transcript/{id} removes transcript data (GDPR). POST /v2/upload uploads audio bytes (returns upload_url for use in transcript submission). WebSocket streaming: wss://api.assemblyai.com/v2/realtime/ws?sample_rate=16000&token={token} for real-time transcription. Webhook: set webhook_url in transcript request; AssemblyAI POSTs transcript object when complete.

API key auth: Authorization: {api_key} header (no Bearer prefix). Keys from AssemblyAI Dashboard → Account → API Key. Account-scoped key. HTTPS enforced; WSS for streaming. No OAuth2. Temporary tokens for client-side streaming: POST /v2/realtime/token (server-side, returns short-lived token for WebSocket auth). PII redaction policies configurable per-request — no API key scoping per-use-case. Key rotation via Dashboard.

Standard HTTP status codes with JSON error bodies. 400 for invalid audio URL or unsupported format. Transcript status: queued → processing → completed or error (with error field describing the failure). Common errors: inaccessible audio URL, unsupported audio codec, audio too short. Webhook delivery: single attempt — implement retry logic on your endpoint or poll as fallback. Streaming: WebSocket disconnects require reconnect; AssemblyAI session tokens expire. Rate limits: plan-dependent; standard free tier limits concurrent transcriptions. AssemblyAI uptime at status.assemblyai.com.

assemblyai.com/docs is excellent — REST API reference, SDK quickstarts (Python, Node.js, Go, Ruby, Java), feature guides for each audio intelligence feature, real-time streaming tutorial, and webhook integration guide. Getting started: sign up (free, $50 credit), get API key, first transcription in under 5 minutes. Python SDK (assemblyai) is idiomatic and well-documented. Free tier generous for evaluation. Developer Discord community active. API Playground in the Dashboard for testing without code.