app.py

import spaces
from pyharp.core import ModelCard, build_endpoint
from pyharp.media.audio import save_audio
from pyharp.labels import LabelList

from audiotools import AudioSignal
from demucs import pretrained
from demucs.apply import apply_model

import gradio as gr
import torch
from pathlib import Path
import numpy as np

# ModelCard
model_card = ModelCard(
    name="Demucs Stem Separator (All Stems)",
    description=(
    "Separates a full music track into four individual audio stems: Drums, Bass, Vocals, Other-instrumental using the Demucs model. Available models are -  \n"
    "htdemucs: Best overall fidelity and natural sound, "
     "mdx_extra: Balanced trade-off, faster processing with a small drop in quality, "
     "mdx_extra_q: Fastest & lightest, noticeable quality loss, ideal for quick previews. \n"
    ),
    author="Alexandre Défossez, et al.",
    tags=["demucs", "source-separation", "pyharp", "stems", "multi-output"]
)

DEMUX_MODELS = ["htdemucs", "mdx_extra", "mdx_extra_q"]
STEM_NAMES = ["Drums", "Bass", "Vocals", "Other"]

# Global model cache
LOADED_MODELS = {}

def get_cached_model(model_name: str):
    if model_name not in LOADED_MODELS:
        model = pretrained.get_model(model_name)
        model.eval()
        device = "cuda" if torch.cuda.is_available() else "cpu"
        model.to(device)
        LOADED_MODELS[model_name] = model
    return LOADED_MODELS[model_name]

# Separation Logic
def separate_all_stems(audio_file_path: str, model_name: str):
    model = get_cached_model(model_name)

    signal = AudioSignal(audio_file_path)
    signal = signal.resample(44100)  # expects 44.1kHz

    is_mono = signal.num_channels == 1
    if is_mono:
        signal.audio_data = signal.audio_data.repeat(2, 1)
        signal._num_channels = 2 

    sr = signal.sample_rate  

    # Ensure audio_data is a torch.Tensor
    audio = signal.audio_data
    if isinstance(audio, np.ndarray):
        audio = torch.from_numpy(audio)

    audio = audio.float()  # [channels, samples] or [channels, samples, ?]

    # Remove extra trailing dimensions
    if audio.ndim > 2:
        audio = audio.squeeze()

    # Final shape: [1, channels, samples]
    waveform = audio.unsqueeze(0)


    with torch.no_grad():
        stems_batch = apply_model(
            model,
            waveform.to(next(model.parameters()).device),
            overlap=0.2,
            shifts=1,
            split=True,
        )

    stems = stems_batch[0]

    output_signals = []
    for stem in stems:
        if is_mono:
            stem = stem.mean(dim=0, keepdim=True)
        signal = AudioSignal(stem.cpu().numpy().astype("float32"), sample_rate=sr)
        output_signals.append(signal)

    # Combine drums + bass + other = instrumental
    drums, bass, other, vocals = output_signals
    instrumental = drums + bass + other

    return [drums, bass, vocals, other]

# Process Function
def process_fn(audio_file_path, model_name):
    if model_name not in DEMUX_MODELS:
        raise ValueError(f"Unsupported model selected: {model_name}")

    output_signals = separate_all_stems(audio_file_path, model_name)

    is_mp3 = Path(audio_file_path).suffix.lower() == ".mp3"
    extension = "mp3" if is_mp3 else "wav"

    outputs = []
    for stem_name, signal in zip(STEM_NAMES, output_signals):
        filename = f"demucs_{model_name}_{stem_name.lower().replace(' ', '_')}.{extension}"
        output_path = Path(filename)

        save_audio(signal, output_path)
        outputs.append(str(output_path))

    return tuple(outputs)

# Gradio App
with gr.Blocks() as demo:
    input_audio = gr.Audio(type="filepath", label="Input Audio").harp_required(True)

    model_dropdown = gr.Dropdown(
        choices=DEMUX_MODELS,
        label="Demucs Model",
        value="htdemucs",
        info=(
            "Choose which Demucs variant to use for separation:\n"
            "1. htdemucs: High-quality Hybrid Transformer Demucs trained on MusDB + 800 songs.\n"
            "2. mdx_extra: Trained with extended data. Balanced model offering a clear trade-off between quality and speed.\n"
            "3. mdx_extra_q: Quantized lightweight version of mdx_extra.\n"
        )
    )

    output_drums = gr.Audio(type="filepath", label="Drums")
    output_bass = gr.Audio(type="filepath", label="Bass")
    output_vocals = gr.Audio(type="filepath", label="Vocals")
    output_instrumental = gr.Audio(type="filepath", label="Other")

    app = build_endpoint(
        model_card=model_card,
        input_components=[input_audio, model_dropdown],
        output_components=[
            output_drums,
            output_bass,
            output_vocals,
            output_instrumental
        ],
        process_fn=process_fn
    )

demo.queue().launch(share=True, show_error=True)