'OpenAI' Compatible Speech-to-Text API Client

A minimal-dependency R client for 'OpenAI'-compatible speech-to-text APIs (see < https://developers.openai.com/api/reference/resources/audio>) with optional local fallbacks. Supports 'OpenAI', local servers, and the 'whisper' package for local transcription.

stt.api

stt.api is a minimal, backend-agnostic R client for OpenAI-compatible speech-to-text (STT) APIs, with optional local fallbacks.

It lets you transcribe audio in R without caring which backend actually performs the transcription.

What stt.api is (and is not)

✅ What it is

• A unified interface for speech-to-text in R

• A way to switch easily between:

  • {whisper} (native R torch, local GPU/CPU, in-process)
  • a self-hosted whisper::serve() endpoint over HTTP (source = "api")
  • OpenAI /v1/audio/transcriptions (cloud or local servers)

• Designed for scripting, Shiny apps, containers, and reproducible pipelines

❌ What it is not

• Not a Whisper reimplementation
• Not a model manager
• Not a GPU / CUDA helper
• Not an audio preprocessing toolkit
• Not a replacement for {whisper}

Installation

install.packages("stt.api")

Required dependencies are minimal:

• curl
• jsonlite

Optional backends:

• {whisper} (recommended, on CRAN)

Development version:

remotes::install_github("cornball-ai/stt.api")

Quick start

install.packages(c("whisper", "stt.api"))

library(stt.api)

res <- stt("speech.wav")
res$text

That's it. With {whisper} installed, stt() transcribes locally on GPU or CPU with no configuration needed.

Other backends

stt.api also supports OpenAI-compatible APIs for cloud or container-based transcription:

set_stt_base("http://localhost:4123")
# Optional, for hosted services like OpenAI
set_stt_key(Sys.getenv("OPENAI_API_KEY"))

res <- stt("speech.wav", backend = "openai")

This works with OpenAI, Whisper containers, LM Studio, OpenWebUI, AnythingLLM, or any server implementing /v1/audio/transcriptions.

Where the engine runs: the source axis

source selects where a backend runs, separately from backend (which engine): "auto" (default), "api" (HTTP), or "package" (in-process). "auto" keeps the previous behavior — whisper in-process, openai via the API — so existing calls are unchanged. To reach a self-hosted whisper::serve() endpoint instead of running whisper in-process:

set_stt_base("http://troy-g5:7809")          # the whisper::serve() endpoint
res <- stt("speech.wav", backend = "whisper", source = "api")

Automatic backend selection

When you call stt() without specifying a backend, it picks the first available:

1. {whisper} (native R torch, if installed)
2. OpenAI-compatible API (if stt.api_base is set)
3. Error with guidance

Normalized output

Regardless of backend, stt() always returns the same structure:

list(
  text     = "Transcribed text",
  segments = NULL | data.frame(...),
  words    = data.frame(word, start, end),  # only with word-level timing
  language = "en",
  backend  = "api" | "whisper",             # legacy execution route
  raw      = <raw backend response>
)

words is present only when the API returns word granularity (verbose_json); otherwise it's absent. backend reports where the engine ran (the legacy execution route), not the engine itself: the resolved backend/source pair lives in the "call_record" attribute.

This makes it easy to switch backends without changing downstream code.

Health checks

stt_health()

Returns:

list(
  ok = TRUE,
  backend = "api",
  message = "OK"
)

Useful for Shiny apps and deployment checks.

Backend selection

Explicit backend choice:

stt("speech.wav", backend = "openai")
stt("speech.wav", backend = "whisper")

Automatic selection (default):

stt("speech.wav")

Supported endpoints

stt.api targets the OpenAI-compatible STT spec:

POST /v1/audio/transcriptions

This is intentionally chosen because it is:

• Widely adopted
• Simple
• Supported by many local and hosted services
• Easy to proxy and containerize

Configuration options

options(
  stt.api_base = NULL,
  stt.api_key  = NULL,
  stt.timeout  = 60
)

Setters:

set_stt_base()
set_stt_key()

Error handling philosophy

• No silent failures
• Clear messages when a backend is unavailable
• Actionable instructions when configuration is missing

Example:

Error in stt():
No transcription backend available.
Install whisper or set stt.api_base.

Relationship to tts.api

stt.api is designed to pair cleanly with tts.api:

Both share:

• Minimal dependencies
• OpenAI-compatible API focus
• Backend-agnostic design
• Optional Docker support

Why this package exists

Installing and maintaining local Whisper backends can be difficult:

• CUDA / cuBLAS issues
• Compiler toolchains
• Platform differences

stt.api lets you decouple your R code from those concerns.

Your transcription code stays the same whether the backend is:

• Local
• Containerized
• Cloud-hosted
• GPU-accelerated
• CPU-only

License

MIT