NeMo-Speech.cpp

A lightweight native C++ runtime for running the NVIDIA Nemotron Speech model family locally, with broad hardware support. It supports multilingual speech recognition, speaker diarization, translation, and speech synthesis in real-time and batch modes.

NeMo-Speech.cpp is NVIDIA's official local speech inference solution, with day-0 support for our latest speech models. It builds on models from NVIDIA NeMo Speech, with native inference powered by ggml.

Models and applications

Application	Supported models
Speech recognition	Nemotron 3.5 ASR Streaming 0.6B, Nemotron Speech Streaming 0.6B, Parakeet TDT 0.6B v3, and Parakeet CTC 1.1B
Speaker diarization	Streaming Sortformer 4-speaker v2, standalone or combined with ASR
Text and speech translation	Riva Translate 4B Instruct v2, with composed ASR-to-NMT-to-TTS speech translation
Speech synthesis	MagpieTTS Multilingual 357M with NeMo NanoCodec
Speech processing	Silero VAD, punctuation and capitalization, endpointing, text normalization, and subtitles

Contents

• Models and applications
• Installation
• Quick start
• Command line
• Local server and playground
• Native SDK
• Build from source
• Documentation
• License
• Contributing

Installation

Install the nemo-speech CLI for the detected platform and backend:

On Linux or macOS, run:

curl -fsSL https://github.com/NVIDIA/NeMo-Speech.cpp/raw/main/scripts/install.sh | sh
export PATH="$HOME/.local/bin:$PATH"  # current shell; future shells are updated

On Windows, run from PowerShell:

irm https://github.com/NVIDIA/NeMo-Speech.cpp/raw/main/scripts/install.ps1 | iex

Open a new PowerShell window after installation so the updated user PATH takes effect.

The installer prefers a verified native release and falls back to a source build when an artifact is unavailable. A source build requires Git, CMake 3.26 or newer, Ninja, a C++17 compiler, SentencePiece development files, and the toolchain required by the selected backend, if any. See Installation for platform-specific prerequisites and options.

Quick start

Transcribe a local WAV file. On first use, the CLI downloads the pinned default Nemotron 3.5 GGUF from Hugging Face and verifies its size and SHA-256:

nemo-speech transcribe /path/to/audio.wav

Source checkouts can use test_files/asr/wav/test/jfk.wav as a smoke-test input.

The same command can transcribe the default microphone on builds that include live capture:

nemo-speech transcribe --live

Run nemo-speech model list to see defaults, short names, and which command uses each model. For example, nemo-speech pull nemotron-en downloads the English-only model ahead of time, and --model nemotron-en selects it. Local GGUF paths continue to work without downloading anything. The CLI selects an available backend and handles common mono or stereo PCM WAV sample rates automatically. See the CLI model guide and model conversion for custom checkpoints.

Command line

The CLI is the primary interface. Run nemo-speech --help to see the capabilities included in your build. The CLI guide covers model selection, GPU controls, directory transcription, subtitles, diarization, translation, synthesis, structured output, and benchmarking when you need them.

Local server and playground

Start the same runtime as a local HTTP service and open the playground:

nemo-speech serve \
  --asr-model nemotron-3.5 \
  --open

The server binds to http://127.0.0.1:8080 by default. Its transcription and speech routes expose documented OpenAI-compatible subsets, alongside realtime WebSocket transcription. A separately built riva_server binary provides the Riva-compatible gRPC interface. See the server guide when you are ready to integrate either interface.

Native SDK

Release archives include stable C headers, shared libraries, and an exported CMake package. An installed application can link only the capability it uses:

find_package(NeMoSpeech REQUIRED COMPONENTS ASR)
target_link_libraries(my_app PRIVATE NeMoSpeech::ASR)

See native SDK integration for in-process C/C++ usage, or client integration for OpenAI SDK, curl, and Riva-compatible gRPC usage.

Build from source

Requires CMake 3.26 or newer, Ninja, C and C++17 compilers, SentencePiece development files, and the toolchain required by the selected backend, if any. For a CUDA ASR and TTS server with the playground:

git submodule update --init ggml llama.cpp third_party/cpp-httplib
scripts/configure.sh cuda-server
cmake --build --preset cuda-server

The configuration helper validates required submodules and applies the pinned ggml patch series for CUDA builds. CPU, Metal, Vulkan, server, component, Windows, and container instructions are in Build from source.

Documentation

Start here	What it covers
Installation	Native releases, Windows, upgrades, and manual verification
CLI guide	Transcription, subtitles, directories, diarization, NMT, TTS, and tooling
Model conversion	Convert NeMo and Hugging Face checkpoints to runtime GGUF files
Servers	HTTP playground/realtime serving and the separate Riva-compatible gRPC server
HTTP API reference	Every endpoint's request fields, responses, and the realtime protocol
Native SDK	CMake components, C ABI lifetimes, threading, and examples
Client integration	OpenAI SDKs, curl, and Riva gRPC clients
Troubleshooting	doctor output and common runtime failures
Build from source	Presets, optional components, dependencies, containers, and artifacts
All documentation	ASR, TTS, NMT, configuration, and developer references

License

NVIDIA-authored code is released under the Apache License 2.0, with the project copyright notice in NOTICE. Third-party components retain their respective terms; see Third-Party Notices. Release archives also include these files under share/licenses/nemo-speech/.

Contributing

External contributions are welcome. See CONTRIBUTING.md for the contribution terms and Developer Certificate of Origin sign-off process.