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Speech and transcription

Generate audio and transcribe files with the V1 audio endpoints.

V1 exposes separate endpoints for text-to-speech and file transcription. They share API-key authentication with chat but use different input formats and billing units.

These are the mappings and validations in the current V1 implementation. Audio service availability is separate from the chat model list; these documentation examples are not evidence of a live audio test.

Generate speech

Send JSON to POST /v1/audio/speech and save the returned audio bytes:

bash

curl --fail-with-body https://api.simplellm.eu/v1/audio/speech \
  -H "Authorization: Bearer $SIMPLELLM_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "tts-1",
    "input": "Welcome to SimpleLLM.",
    "voice": "alloy",
    "response_format": "mp3",
    "speed": 1
  }' \
  --output speech.mp3

Field	Default	V1 behavior
`input`	Required	Nonempty, at most 4096 UTF-8 bytes
`model`	`tts-1`	Forwarded to the configured speech service
`voice`	`alloy`	alloy, echo, fable, onyx, nova, shimmer
`response_format`	`mp3`	mp3, opus, aac, flac, wav, pcm
`speed`	1	0.25 to 4; zero is normalized to the default

The response is binary audio, not JSON containing an audio URL. Check HTTP status before treating the saved body as a valid audio file; an error body can contain JSON instead.

UTF-8 bytes are not the same as characters. Non-ASCII text can reach the input limit with fewer than 4096 characters.

Transcribe a file

Send multipart form data to POST /v1/audio/transcriptions:

bash

curl --fail-with-body https://api.simplellm.eu/v1/audio/transcriptions \
  -H "Authorization: Bearer $SIMPLELLM_API_KEY" \
  -F 'file=@recording.wav' \
  -F 'model=whisper-large-v3-turbo' \
  -F 'language=en' \
  -F 'response_format=json'

Do not manually set a multipart Content-Type header when using cURL or a form-data library: the client must include its generated boundary.

The two explicit V1 model mappings are:

Model ID	Mapping	Configured SC/min
`whisper-large-v3-turbo`	Turbo transcription	0.5
`whisper-large-v3`	Large-v3 transcription	1.5

The compatibility name whisper-1 maps to whisper-large-v3-turbo; it is not another model. Omitting the model selects this alias, but explicit IDs are clearer for new integrations.

Optional transcription fields

language, prompt, response_format, and temperature are forwarded to the transcription service. For language, use a two-letter code such as de or en; omit it when automatic detection is desired instead of sending a UI label.

JSON responses contain text, for example:

json

{"text": "Welcome to SimpleLLM."}

Other output formats depend on the upstream service. Inspect Content-Type and do not force every returned body through a JSON parser.

Audio billing and limitations

Current V1 speech billing is 3 SC per 1000 input UTF-8 bytes. Transcription uses the configured per-minute rate and an estimated duration derived from file size and extension; it is not guaranteed to be an exact measured duration.

These implementation rates were checked on 2026-09-14 and are distinct from chat's per-million-token pricing. Confirm current account pricing before budgeting a larger workload.

The direct GPU-host voice catalogue, voice design, and voice cloning features are not part of this public V1 interface. See the speech reference and transcription reference.