huggingface--transformers/docs/source/en/model_doc/nemotron_asr_streaming.md

This model was published in HF papers on 2023-05-08 and contributed to Hugging Face Transformers on 2026-06-18.

Nemotron ASR Streaming

Overview

Nemotron ASR Streaming is a 600M-parameter English speech recognition model from NVIDIA, built for high-quality transcription in both low-latency streaming and high-throughput batch settings, with native punctuation and capitalization. For streaming, it offers configurable chunk sizes—80ms, 160ms, 560ms, and 1120ms, letting users trade off latency against accuracy to suit their application. Its cache-aware FastConformer-RNNT architecture is central to this capability: unlike traditional buffered streaming, which repeatedly reprocesses overlapping audio windows, the model processes only each new incoming chunk while reusing cached encoder context from prior chunks. This eliminates redundant computation, significantly improves efficiency, and minimizes end-to-end delay without sacrificing accuracy, making it well suited to real-time transcription workloads.

Usage

Offline transcription

from transformers import pipeline

pipe = pipeline(
    "automatic-speech-recognition",
    model="nvidia/nemotron-speech-streaming-en-0.6b",
)
out = pipe("https://huggingface.co/datasets/hf-internal-testing/dummy-audio-samples/resolve/main/bcn_weather.mp3")
print(out)

from transformers import AutoModelForRNNT, AutoProcessor
from transformers.audio_utils import load_audio

model_id = "nvidia/nemotron-speech-streaming-en-0.6b"
processor = AutoProcessor.from_pretrained(model_id)
model = AutoModelForRNNT.from_pretrained(model_id, device_map="auto")

audio = load_audio(
    "https://huggingface.co/datasets/hf-internal-testing/dummy-audio-samples/resolve/main/bcn_weather.mp3",
    sampling_rate=processor.feature_extractor.sampling_rate,
)

inputs = processor(audio, sampling_rate=processor.feature_extractor.sampling_rate)
inputs.to(model.device, dtype=model.dtype)
output = model.generate(**inputs, return_dict_in_generate=True)
print(processor.decode(output.sequences, skip_special_tokens=True))

Streaming transcription

Note

This is an experimental feature and the API is subject to change.

For real-time transcription, audio is split into chunks following:

from threading import Thread
from transformers import AutoModelForRNNT, AutoProcessor, TextIteratorStreamer
from transformers.audio_utils import load_audio

model_id = "nvidia/nemotron-speech-streaming-en-0.6b"
processor = AutoProcessor.from_pretrained(model_id)
model = AutoModelForRNNT.from_pretrained(model_id, device_map="auto")

processor.set_num_lookahead_tokens(6)
print(f"Streaming latency: {processor.streaming_latency_ms} ms")

sampling_rate = processor.feature_extractor.sampling_rate
audio = load_audio(
    "https://huggingface.co/datasets/hf-internal-testing/dummy-audio-samples/resolve/main/obama.mp3",
    sampling_rate=sampling_rate,
)

first_chunk_inputs = processor(
    audio[: processor.num_samples_first_audio_chunk],
    sampling_rate=sampling_rate,
    is_streaming=True,
    is_first_audio_chunk=True,
    return_tensors="pt",
)
first_chunk_inputs = first_chunk_inputs.to(model.device, dtype=model.dtype)


def input_features_generator():
    yield first_chunk_inputs.input_features[:, : processor.num_mel_frames_first_audio_chunk, :]

    mel_frame_idx = processor.num_mel_frames_first_audio_chunk
    hop_length = processor.feature_extractor.hop_length
    n_fft = processor.feature_extractor.n_fft

    start_idx = mel_frame_idx * hop_length - n_fft // 2
    while (end_idx := start_idx + processor.num_samples_per_audio_chunk) < audio.shape[0]:
        inputs = processor(
            audio[start_idx:end_idx],
            sampling_rate=sampling_rate,
            is_streaming=True,
            is_first_audio_chunk=False,
            return_tensors="pt",
        )
        inputs = inputs.to(model.device, dtype=model.dtype)
        yield inputs.input_features

        mel_frame_idx += processor.num_mel_frames_per_audio_chunk
        start_idx = mel_frame_idx * hop_length - n_fft // 2


streamer = TextIteratorStreamer(processor.tokenizer, skip_special_tokens=True)
generate_kwargs = {
    **first_chunk_inputs,
    "input_features": input_features_generator(),
    "streamer": streamer,
}
thread = Thread(target=model.generate, kwargs=generate_kwargs)
thread.start()

# Iterate over the streamer to get text chunks as they are generated
print("Model output (streaming):", end=" ", flush=True)
for text_chunk in streamer:
    print(text_chunk, end="", flush=True)
thread.join()

Streaming latency

The latency is set by num_lookahead_tokens, the right attention context (lookahead, in subsampled encoder frames) each chunk waits for before it is emitted. A larger value lets each chunk see more future audio: better accuracy at the cost of higher latency. Inspect the supported trade-offs, select one, and read back the resulting latency:

from transformers import AutoProcessor

processor = AutoProcessor.from_pretrained("nvidia/nemotron-speech-streaming-en-0.6b")

# Each supported `num_lookahead_tokens` mapped to its streaming latency in milliseconds:
print(processor.supported_streaming_latencies_ms)
# {13: 1120, 6: 560, 1: 160, 0: 80}

# Select a right attention context (this also re-derives the streaming chunk sizes used above):
processor.set_num_lookahead_tokens(6)

# Latency of the current selection:
print(processor.streaming_latency_ms)
# 560

set_num_lookahead_tokens sizes the chunks the processor emits, and the matching num_lookahead_tokens must reach generate (in the snippet above it travels through **inputs/**first_chunk_inputs, which carries num_lookahead_tokens). Streaming generate raises if it is omitted.

NemotronAsrStreamingConfig

autodoc NemotronAsrStreamingConfig

NemotronAsrStreamingEncoderConfig

autodoc NemotronAsrStreamingEncoderConfig

NemotronAsrStreamingFeatureExtractor

autodoc NemotronAsrStreamingFeatureExtractor

NemotronAsrStreamingProcessor

autodoc NemotronAsrStreamingProcessor - call - decode

NemotronAsrStreamingEncoderModelOutput

autodoc NemotronAsrStreamingEncoderModelOutput

NemotronAsrStreamingRNNTOutput

autodoc NemotronAsrStreamingRNNTOutput

NemotronAsrStreamingEncoder

autodoc NemotronAsrStreamingEncoder - forward

NemotronAsrStreamingForRNNT

autodoc NemotronAsrStreamingForRNNT - forward - generate