feat(moss-tts-nano): add single-stage MOSS-TTS-Nano TTS support

Integrates OpenMOSS-Team/MOSS-TTS-Nano (0.1B) as a single
GPUGenerationWorker stage.  Both the AR LM and MOSS-Audio-Tokenizer-Nano
codec run inside MossTTSNanoForGeneration.forward(), removing the need for
an inter-stage connector.

Key design choices:
- Weights loaded in load_weights() not __init__ (avoids pre-CUDA alloc)
- trust_remote_code delegates to upstream HF model classes
- codec path read from config.audio_tokenizer_pretrained_name_or_path
- inference_stream() collects progressive audio chunks for low latency
- 48 kHz stereo output; voice clone + continuation modes supported


Signed-off-by: Yueqian Lin <linyueqian@outlook.com>

examples/offline_inference/moss_tts_nano/end2end.py

@@ -0,0 +1,184 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Offline inference example for MOSS-TTS-Nano via vLLM-Omni.
+
+Single-stage pipeline: the 0.1B AR LM and MOSS-Audio-Tokenizer-Nano codec
+both run inside one generation stage.  Output is 48 kHz stereo WAV.
+
+Supports:
+  - Built-in voice presets (--voice)
+  - Custom voice cloning via reference audio (--prompt-audio)
+  - Batch synthesis of multiple texts
+  - Reproducible output via --seed
+
+Usage examples:
+  # Built-in voice
+  python end2end.py --text "Hello from MOSS-TTS-Nano."
+
+  # Voice clone with reference audio
+  python end2end.py --text "Hello!" --prompt-audio /path/to/ref.wav
+
+  # Batch with different voices
+  python end2end.py --batch --output-dir /tmp/moss_output
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import soundfile as sf
+import torch
+from vllm import SamplingParams
+from vllm.utils.argparse_utils import FlexibleArgumentParser
+
+# Prevent multiprocessing from re-importing CUDA in the wrong context.
+os.environ.setdefault("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
+
+from vllm_omni import Omni  # noqa: E402
+
+MODEL = "OpenMOSS-Team/MOSS-TTS-Nano"
+
+_REPO_ROOT = Path(__file__).resolve().parents[4]
+DEFAULT_STAGE_CONFIG = str(
+    _REPO_ROOT / "vllm_omni" / "model_executor" / "stage_configs" / "moss_tts_nano.yaml"
+)
+
+BATCH_SAMPLES = [
+    {"text": "Hello, this is a test of MOSS-TTS-Nano.", "voice": "Ava", "label": "en_hello"},
+    {"text": "你好，这是 MOSS-TTS-Nano 的语音合成测试。", "voice": "Junhao", "label": "zh_hello"},
+    {"text": "Bonjour, ceci est un test de synthèse vocale.", "voice": "Bella", "label": "fr_hello"},
+]
+
+
+def build_request(
+    text: str,
+    voice: str = "Junhao",
+    mode: str = "voice_clone",
+    prompt_audio_path: str | None = None,
+    prompt_text: str | None = None,
+    max_new_frames: int = 375,
+    seed: int | None = None,
+    audio_temperature: float = 0.8,
+    audio_top_k: int = 25,
+    audio_top_p: float = 0.95,
+    text_temperature: float = 1.0,
+) -> dict:
+    """Build an Omni request payload for MOSS-TTS-Nano."""
+    additional: dict = {
+        "text": [text],
+        "voice": [voice],
+        "mode": [mode],
+        "max_new_frames": [max_new_frames],
+        "audio_temperature": [audio_temperature],
+        "audio_top_k": [audio_top_k],
+        "audio_top_p": [audio_top_p],
+        "text_temperature": [text_temperature],
+    }
+    if prompt_audio_path:
+        additional["prompt_audio_path"] = [str(prompt_audio_path)]
+    if prompt_text:
+        additional["prompt_text"] = [prompt_text]
+    if seed is not None:
+        additional["seed"] = [seed]
+
+    return {
+        "prompt": "<|im_start|>assistant\n",  # minimal placeholder prompt
+        "additional_information": additional,
+    }
+
+
+def save_audio(waveform: torch.Tensor, path: str, sample_rate: int = 48000) -> None:
+    audio_np = waveform.float().numpy()
+    # Reshape stereo: inference_stream yields interleaved [samples*2]; reshape to [samples, 2]
+    if audio_np.ndim == 1 and audio_np.shape[0] % 2 == 0:
+        audio_np = audio_np.reshape(-1, 2)
+    sf.write(path, audio_np, sample_rate)
+    print(f"  Saved {path} ({audio_np.shape}, {sample_rate} Hz)")
+
+
+def main(args) -> None:
+    omni = Omni(
+        model=MODEL,
+        stage_configs_path=args.stage_config,
+        stage_init_timeout=args.stage_init_timeout,
+    )
+
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        top_p=1.0,
+        top_k=50,
+        max_tokens=4096,
+        seed=args.seed if args.seed is not None else 42,
+        detokenize=False,
+    )
+
+    output_dir = Path(args.output_dir)
+    output_dir.mkdir(parents=True, exist_ok=True)
+
+    if args.batch:
+        print(f"Running batch synthesis ({len(BATCH_SAMPLES)} samples)...")
+        inputs = [
+            build_request(s["text"], voice=s["voice"], seed=args.seed)
+            for s in BATCH_SAMPLES
+        ]
+        params_list = [sampling_params] * len(inputs)
+    else:
+        print(f"Synthesizing: {args.text!r}")
+        inputs = build_request(
+            text=args.text,
+            voice=args.voice,
+            mode=args.mode,
+            prompt_audio_path=args.prompt_audio,
+            prompt_text=args.prompt_text,
+            max_new_frames=args.max_new_frames,
+            seed=args.seed,
+            audio_temperature=args.audio_temperature,
+            audio_top_k=args.audio_top_k,
+            audio_top_p=args.audio_top_p,
+            text_temperature=args.text_temperature,
+        )
+        params_list = sampling_params
+
+    for stage_outputs in omni.generate(inputs, params_list):
+        for i, req_output in enumerate(stage_outputs.request_output):
+            for j, out in enumerate(req_output.outputs):
+                mm = out.multimodal_output
+                if mm is None:
+                    print(f"  [req {i}] No audio output.")
+                    continue
+                audio = mm.get("audio")
+                sr_tensor = mm.get("sr")
+                if audio is None:
+                    print(f"  [req {i}] No waveform in multimodal_output.")
+                    continue
+                sr = int(sr_tensor.item()) if sr_tensor is not None else 48000
+                label = BATCH_SAMPLES[i]["label"] if args.batch else f"output_{i}_{j}"
+                out_path = str(output_dir / f"{label}.wav")
+                save_audio(audio.cpu(), out_path, sr)
+
+    print("Done.")
+
+
+def parse_args():
+    parser = FlexibleArgumentParser(description="MOSS-TTS-Nano offline inference")
+    parser.add_argument("--text", default="Hello, this is MOSS-TTS-Nano speaking.", help="Text to synthesize.")
+    parser.add_argument("--voice", default="Junhao", help="Built-in voice preset name.")
+    parser.add_argument("--mode", default="voice_clone", choices=["voice_clone", "continuation"])
+    parser.add_argument("--prompt-audio", default=None, help="Path to reference audio for voice cloning.")
+    parser.add_argument("--prompt-text", default=None, help="Reference transcript (continuation mode).")
+    parser.add_argument("--max-new-frames", type=int, default=375, help="Max AR frames (~14s at default).")
+    parser.add_argument("--seed", type=int, default=None, help="Random seed.")
+    parser.add_argument("--audio-temperature", type=float, default=0.8)
+    parser.add_argument("--audio-top-k", type=int, default=25)
+    parser.add_argument("--audio-top-p", type=float, default=0.95)
+    parser.add_argument("--text-temperature", type=float, default=1.0)
+    parser.add_argument("--batch", action="store_true", help="Run built-in batch of diverse samples.")
+    parser.add_argument("--output-dir", default="/tmp/moss_tts_nano_output", help="Directory for WAV outputs.")
+    parser.add_argument("--stage-config", default=DEFAULT_STAGE_CONFIG)
+    parser.add_argument("--stage-init-timeout", type=int, default=120)
+    return parser.parse_args()
+
+
+if __name__ == "__main__":
+    main(parse_args())