LocalAI/docs/content/features/audio-to-text.md

+++ disableToc = false title = "Audio to Text" weight = 16 url = "/features/audio-to-text/" +++

Audio to text models are models that can generate text from an audio file.

The transcription endpoint allows to convert audio files to text. The endpoint supports multiple backends:

• whisper.cpp: A C++ library for audio transcription (default)
• moonshine: Ultra-fast transcription engine optimized for low-end devices
• faster-whisper: Fast Whisper implementation with CTranslate2
• parakeet-cpp: A C++/ggml port of NVIDIA NeMo Parakeet (FastConformer TDT/CTC/RNNT/hybrid). Runs quantized GGUFs on CPU or GPU, emits word-level timestamps, and supports cache-aware streaming (the realtime_eou model surfaces end-of-utterance events).
• llama-cpp: Route transcription to any multimodal-audio GGUF model served by the llama-cpp backend (e.g. Qwen3-ASR, Voxtral, Qwen2-Audio). Under the hood the request is converted into a chat completion with the audio attached via the model's audio encoder — the same path the upstream llama.cpp server uses. Set backend: llama-cpp in the model YAML and point mmproj at the matching audio encoder.
• voxtral: Voxtral-family models served by a dedicated backend

The endpoint input supports all the audio formats supported by ffmpeg.

Looking for "who spoke when" instead of a flat transcript? See Speaker Diarization — /v1/audio/diarization returns time-stamped speaker segments and supports the rttm format used by pyannote.metrics.

Usage

Once LocalAI is started and whisper models are installed, you can use the /v1/audio/transcriptions API endpoint.

For instance, with cURL:

curl http://localhost:8080/v1/audio/transcriptions -H "Content-Type: multipart/form-data" -F file="@<FILE_PATH>" -F model="<MODEL_NAME>"

Example

Download one of the models from here in the models folder, and create a YAML file for your model:

name: whisper-1
backend: whisper
parameters:
  model: whisper-en

The transcriptions endpoint then can be tested like so:

## Get an example audio file
wget --quiet --show-progress -O gb1.ogg https://upload.wikimedia.org/wikipedia/commons/1/1f/George_W_Bush_Columbia_FINAL.ogg

## Send the example audio file to the transcriptions endpoint
curl http://localhost:8080/v1/audio/transcriptions -H "Content-Type: multipart/form-data" -F file="@$PWD/gb1.ogg" -F model="whisper-1"

Result:

{
  "segments":[{"id":0,"start":0,"end":9640000000,"text":" My fellow Americans, this day has brought terrible news and great sadness to our country.","tokens":[50364,1222,7177,6280,11,341,786,575,3038,6237,2583,293,869,22462,281,527,1941,13,50846]},{"id":1,"start":9640000000,"end":15960000000,"text":" At 9 o'clock this morning, Mission Control and Houston lost contact with our Space Shuttle","tokens":[1711,1722,277,6,9023,341,2446,11,20170,12912,293,18717,2731,3385,365,527,8705,13870,10972,51162]},{"id":2,"start":15960000000,"end":16960000000,"text":" Columbia.","tokens":[17339,13,51212]},{"id":3,"start":16960000000,"end":24640000000,"text":" A short time later, debris was seen falling from the skies above Texas.","tokens":[316,2099,565,1780,11,21942,390,1612,7440,490,264,25861,3673,7885,13,51596]},{"id":4,"start":24640000000,"end":27200000000,"text":" The Columbia's lost.","tokens":[440,17339,311,2731,13,51724]},{"id":5,"start":27200000000,"end":29920000000,"text":" There are no survivors.","tokens":[821,366,572,18369,13,51860]},{"id":6,"start":29920000000,"end":32920000000,"text":" And board was a crew of seven.","tokens":[50364,400,3150,390,257,7260,295,3407,13,50514]},{"id":7,"start":32920000000,"end":39780000000,"text":" Colonel Rick Husband, Lieutenant Colonel Michael Anderson, Commander Laurel Clark, Captain","tokens":[28478,11224,21282,4235,11,28412,28478,5116,18768,11,20857,27270,75,18572,11,10873,50857]},{"id":8,"start":39780000000,"end":50020000000,"text":" David Brown, Commander William McCool, Dr. Cooltna Chavla, and Elon Ramon, a Colonel","tokens":[4389,8030,11,20857,6740,4050,34,1092,11,2491,13,8561,83,629,761,706,875,11,293,28498,9078,266,11,257,28478,51369]},{"id":9,"start":50020000000,"end":52800000000,"text":" in the Israeli Air Force.","tokens":[294,264,19974,5774,10580,13,51508]},{"id":10,"start":52800000000,"end":58480000000,"text":" These men and women assumed great risk in the service to all humanity.","tokens":[1981,1706,293,2266,15895,869,3148,294,264,2643,281,439,10243,13,51792]},{"id":11,"start":58480000000,"end":63120000000,"text":" And an age when Space Flight has come to seem almost routine.","tokens":[50364,400,364,3205,562,8705,28954,575,808,281,1643,1920,9927,13,50596]},{"id":12,"start":63120000000,"end":68800000000,"text":" It is easy to overlook the dangers of travel by rocket and the difficulties of navigating","tokens":[467,307,1858,281,37826,264,27701,295,3147,538,13012,293,264,14399,295,32054,50880]},{"id":13,"start":68800000000,"end":72640000000,"text":" the fierce outer atmosphere of the Earth.","tokens":[264,25341,10847,8018,295,264,4755,13,51072]},{"id":14,"start":72640000000,"end":78040000000,"text":" These astronauts knew the dangers and they faced them willingly.","tokens":[1981,28273,2586,264,27701,293,436,11446,552,44675,13,51342]},{"id":15,"start":78040000000,"end":83040000000,"text":" Knowing they had a high and noble purpose in life.","tokens":[25499,436,632,257,1090,293,20171,4334,294,993,13,51592]},{"id":16,"start":83040000000,"end":90800000000,"text":" Because of their courage and daring and idealism, we will miss them all the more.","tokens":[50364,1436,295,641,9892,293,43128,293,7157,1434,11,321,486,1713,552,439,264,544,13,50752]},{"id":17,"start":90800000000,"end":96560000000,"text":" All Americans today are thinking as well of the families of these men and women who have","tokens":[1057,6280,965,366,1953,382,731,295,264,4466,295,613,1706,293,2266,567,362,51040]},{"id":18,"start":96560000000,"end":100440000000,"text":" been given this sudden shock in grief.","tokens":[668,2212,341,3990,5588,294,18998,13,51234]},{"id":19,"start":100440000000,"end":102400000000,"text":" You're not alone.","tokens":[509,434,406,3312,13,51332]},{"id":20,"start":102400000000,"end":105440000000,"text":" Our entire nation agrees with you.","tokens":[2621,2302,4790,26383,365,291,13,51484]},{"id":21,"start":105440000000,"end":112360000000,"text":" And those you loved will always have the respect and gratitude of this country.","tokens":[400,729,291,4333,486,1009,362,264,3104,293,16935,295,341,1941,13,51830]},{"id":22,"start":112360000000,"end":116600000000,"text":" The cause in which they died will continue.","tokens":[50364,440,3082,294,597,436,4539,486,2354,13,50576]},{"id":23,"start":116600000000,"end":124240000000,"text":" Man kind is led into the darkness beyond our world by the inspiration of discovery and the","tokens":[2458,733,307,4684,666,264,11262,4399,527,1002,538,264,10249,295,12114,293,264,50958]},{"id":24,"start":124240000000,"end":127000000000,"text":" longing to understand.","tokens":[35050,281,1223,13,51096]},{"id":25,"start":127000000000,"end":131160000000,"text":" Our journey into space will go on.","tokens":[2621,4671,666,1901,486,352,322,13,51304]},{"id":26,"start":131160000000,"end":136480000000,"text":" In the skies today, we saw destruction and tragedy.","tokens":[682,264,25861,965,11,321,1866,13563,293,18563,13,51570]},{"id":27,"start":136480000000,"end":142080000000,"text":" As farther than we can see, there is comfort and hope.","tokens":[1018,20344,813,321,393,536,11,456,307,3400,293,1454,13,51850]},{"id":28,"start":142080000000,"end":149800000000,"text":" In the words of the prophet Isaiah, lift your eyes and look to the heavens who created","tokens":[50364,682,264,2283,295,264,18566,27263,11,5533,428,2575,293,574,281,264,26011,567,2942,50750]},{"id":29,"start":149800000000,"end":151640000000,"text":" all these.","tokens":[439,613,13,50842]},{"id":30,"start":151640000000,"end":159960000000,"text":" He who brings out the story hosts one by one and calls them each by name because of his great","tokens":[634,567,5607,484,264,1657,21573,472,538,472,293,5498,552,1184,538,1315,570,295,702,869,51258]},{"id":31,"start":159960000000,"end":163400000000,"text":" power and mighty strength.","tokens":[1347,293,21556,3800,13,51430]},{"id":32,"start":163400000000,"end":166400000000,"text":" Not one of them is missing.","tokens":[1726,472,295,552,307,5361,13,51580]},{"id":33,"start":166400000000,"end":173600000000,"text":" The same creator who names the stars also knows the names of the seven souls we mourn","tokens":[50364,440,912,14181,567,5288,264,6105,611,3255,264,5288,295,264,3407,16588,321,22235,77,50724]},{"id":34,"start":173600000000,"end":175600000000,"text":" today.","tokens":[965,13,50824]},{"id":35,"start":175600000000,"end":183160000000,"text":" The crew of the shuttle Columbia did not return safely to earth yet we can pray that all","tokens":[440,7260,295,264,26728,17339,630,406,2736,11750,281,4120,1939,321,393,3690,300,439,51202]},{"id":36,"start":183160000000,"end":185840000000,"text":" are safely home.","tokens":[366,11750,1280,13,51336]},{"id":37,"start":185840000000,"end":192600000000,"text":" May God bless the grieving families and may God continue to bless America.","tokens":[1891,1265,5227,264,48454,4466,293,815,1265,2354,281,5227,3374,13,51674]},{"id":38,"start":196400000000,"end":206400000000,"text":" [BLANK_AUDIO]","tokens":[50364,542,37592,62,29937,60,50864]}],
  "text":"My fellow Americans, this day has brought terrible news and great sadness to our country. At 9 o'clock this morning, Mission Control and Houston lost contact with our Space Shuttle Columbia. A short time later, debris was seen falling from the skies above Texas. The Columbia's lost. There are no survivors. And board was a crew of seven. Colonel Rick Husband, Lieutenant Colonel Michael Anderson, Commander Laurel Clark, Captain David Brown, Commander William McCool, Dr. Cooltna Chavla, and Elon Ramon, a Colonel in the Israeli Air Force. These men and women assumed great risk in the service to all humanity. And an age when Space Flight has come to seem almost routine. It is easy to overlook the dangers of travel by rocket and the difficulties of navigating the fierce outer atmosphere of the Earth. These astronauts knew the dangers and they faced them willingly. Knowing they had a high and noble purpose in life. Because of their courage and daring and idealism, we will miss them all the more. All Americans today are thinking as well of the families of these men and women who have been given this sudden shock in grief. You're not alone. Our entire nation agrees with you. And those you loved will always have the respect and gratitude of this country. The cause in which they died will continue. Man kind is led into the darkness beyond our world by the inspiration of discovery and the longing to understand. Our journey into space will go on. In the skies today, we saw destruction and tragedy. As farther than we can see, there is comfort and hope. In the words of the prophet Isaiah, lift your eyes and look to the heavens who created all these. He who brings out the story hosts one by one and calls them each by name because of his great power and mighty strength. Not one of them is missing. The same creator who names the stars also knows the names of the seven souls we mourn today. The crew of the shuttle Columbia did not return safely to earth yet we can pray that all are safely home. May God bless the grieving families and may God continue to bless America. [BLANK_AUDIO]"
}

---

You can also specify the response_format parameter to be one of lrc, srt, vtt, text, json or verbose_json (default):

## Send the example audio file to the transcriptions endpoint
curl http://localhost:8080/v1/audio/transcriptions -H "Content-Type: multipart/form-data" -F file="@$PWD/gb1.ogg" -F model="whisper-1" -F response_format="srt"

Result (first few lines):

1
00:00:00,000 --> 00:00:09,640
My fellow Americans, this day has brought terrible news and great sadness to our country.

2
00:00:09,640 --> 00:00:15,960
At 9 o'clock this morning, Mission Control and Houston lost contact with our Space Shuttle

3
00:00:15,960 --> 00:00:16,960
Columbia.

4
00:00:16,960 --> 00:00:24,640
A short time later, debris was seen falling from the skies above Texas.

5
00:00:24,640 --> 00:00:27,200
The Columbia's lost.

6
00:00:27,200 --> 00:00:29,920
There are no survivors.

Supported request parameters

In addition to file and model, the endpoint accepts the following multipart form fields, matching the OpenAI audio transcription API:

Field	Description
language	ISO-639-1 language hint (e.g. en). Passed through to the backend.
prompt	Optional context hint to bias the decoder.
temperature	Sampling temperature (float). Honored by backends that support it.
timestamp_granularities[]	Multi-value form field: word and/or segment. Honored when the backend produces the requested granularity.
response_format	One of json (default for backwards-compat), verbose_json, text, srt, vtt, lrc.
stream	When true, the endpoint emits an SSE stream of transcript.text.delta events followed by a final transcript.text.done event.
diarize	LocalAI extension — speaker diarization (whisper.cpp only).

The response body for verbose_json includes text, language, duration, and segments[] (with speaker populated when diarization is enabled).

Streaming transcriptions

Set -F stream=true to receive token-by-token SSE events as the backend produces them. The event shape matches the OpenAI streaming transcription format:

curl -N http://localhost:8080/v1/audio/transcriptions \
  -H "Content-Type: multipart/form-data" \
  -F file="@sample.wav" \
  -F model="whisper-1" \
  -F stream=true

data: {"type":"transcript.text.delta","delta":"And so, my"}

data: {"type":"transcript.text.delta","delta":" fellow Americans..."}

data: {"type":"transcript.text.done","text":"And so, my fellow Americans..."}

data: [DONE]

Backends that do not natively stream tokens fall back to emitting one delta plus a done event with the full text — the SSE contract is identical either way.

Using the llama-cpp backend with an audio-capable model

Any GGUF model whose mmproj contains an audio encoder can be used for transcription via the llama-cpp backend. This reuses the model's own audio front-end rather than shelling out to whisper.cpp, which is useful when you want a single backend serving both chat-with-audio and transcription.

Example using ggml-org/Qwen3-ASR-0.6B-GGUF:

name: qwen3-asr
backend: llama-cpp
parameters:
  model: Qwen3-ASR-0.6B-Q8_0.gguf
mmproj: mmproj-Qwen3-ASR-0.6B-Q8_0.gguf

Then call /v1/audio/transcriptions as usual:

curl http://localhost:8080/v1/audio/transcriptions \
  -H "Content-Type: multipart/form-data" \
  -F file="@jfk.wav" \
  -F model="qwen3-asr"

Using the parakeet-cpp backend

parakeet.cpp is a C++/ggml port of NVIDIA NeMo Parakeet that matches the upstream PyTorch models on CPU. GGUF weights for every model and quant are published in a single repo, mudler/parakeet-cpp-gguf. F16 is the recommended default, and Q4_K stays near-lossless on the small models. The easiest path is to import directly (the GGUFs auto-detect to this backend):

local-ai models import https://huggingface.co/mudler/parakeet-cpp-gguf/resolve/main/tdt_ctc-110m-f16.gguf

Or write a model YAML:

name: parakeet-110m
backend: parakeet-cpp
parameters:
  model: tdt_ctc-110m-f16.gguf

Then call /v1/audio/transcriptions as usual. Pass timestamp_granularities[]=word for per-word timings:

curl http://localhost:8080/v1/audio/transcriptions \
  -H "Content-Type: multipart/form-data" \
  -F file="@jfk.wav" \
  -F model="parakeet-110m" \
  -F "timestamp_granularities[]=word"

For real-time use, load a cache-aware streaming model (e.g. realtime_eou_120m-v1-*.gguf) and pass -F stream=true. Deltas are emitted as the audio is decoded, with end-of-utterance events closing each segment.

Segment timestamps

Transcriptions are split into segments the same way NVIDIA NeMo does: a new segment starts after sentence-ending punctuation (., ?, !), and each segment carries start/end times. This is the default (NeMo's punctuation-only segmentation) and needs no configuration. While streaming, each end-of-utterance closes a segment, now with timestamps.

You can additionally split on silence by setting segment_gap_threshold (NeMo's segment_gap_threshold, in encoder frames; off by default). When set, a gap between two words wider than the threshold also starts a new segment. The value is in frames to match NeMo exactly; the backend converts it to seconds using the model's frame stride (frame_sec, reported by the engine):

name: parakeet-110m
backend: parakeet-cpp
parameters:
  model: tdt_ctc-110m-f16.gguf
options:
- segment_gap_threshold:12   # split on silence > 12 encoder frames (default 0 = off, punctuation-only)

Dynamic batching

The backend can coalesce concurrent transcription requests into a single batched engine call, which improves throughput on GPU when many requests arrive at once. Batching is off by default (batch_max_size:1, one request at a time); raise it to opt in. Two options: knobs control it:

name: parakeet-110m
backend: parakeet-cpp
parameters:
  model: tdt_ctc-110m-f16.gguf
options:
- batch_max_size:8      # max requests coalesced into one batch (default 1 = off)
- batch_max_wait_ms:15  # how long to wait to fill a batch, in ms (default 15)

By default each request runs on its own. Raise batch_max_size (for example 4 to 16) to enable batching; it pays off on GPU under concurrent load, where coalescing the per-step decode GEMMs across requests is a large throughput win. Leave it at 1 on CPU and for low-concurrency setups, where batching only adds latency. Batching only affects concurrent unary requests; streaming sessions always run on their own.

See also

• [Audio Transform]({{< relref "audio-transform.md" >}}) — clean up the audio (echo cancellation, noise suppression, dereverberation) before passing it to a transcription model.