stem_render.py

# stem_render.py — Stem-based rendering with demucs

import numpy as np
import scipy.io.wavfile
import tempfile
import logging
import gradio as gr

logger = logging.getLogger("dj_engine")


def render_full_set_with_stems(app_state, max_iter=20, stem_backend="spleeter", progress=gr.Progress()):
    """Render the DJ set using stem separation.
    
    max_iter: number of refinement iterations (from the UI slider)
    stem_backend: specify 'demucs', 'demucs-mlx', or 'spleeter'. Defaults to preferred_stem_backend()
    """
    if not app_state.transitions:
        return None, "⚠️ Generate a set plan first"

    progress(0.02, desc="Starting stem-based render...")
    sr = 44100

    try:
        from stem_mixer import mix_stems
        from stem_separator import preferred_stem_backend, separate_stems_with_backend

        actual_backend = stem_backend if stem_backend else preferred_stem_backend()
        progress(0.03, desc=f"Loading stem separator ({actual_backend})...")

        # Separate each track into stems (cache-aware — skips separation on cache hit)
        all_stems = {}
        backend_used = actual_backend
        n_tracks = len(app_state.set_order)
        for i, tidx in enumerate(app_state.set_order):
            track = app_state.analyses[tidx]
            progress(0.03 + (i / n_tracks) * 0.50,
                     desc=f"Separating stems ({actual_backend}, {i+1}/{n_tracks}): {track.filename[:30]}...")

            stems, backend_used = separate_stems_with_backend(track.path, 0.0, None, sr, backend=stem_backend)
            all_stems[tidx] = stems
            logger.info(f"Stems for {track.filename} via {backend_used}: {list(stems.keys())}")

        # Mix using stem mixer
        progress(0.55, desc="Mixing with stems (surgical drum/bass swap)...")
        set_audio, set_info = mix_stems(
            all_stems, app_state.analyses, app_state.set_order,
            progress_cb=lambda p, m: progress(0.55 + p * 0.35, desc=m)
        )
        method = f"{backend_used} htdemucs → surgical drum/bass swap on downbeats"

    except Exception as e:
        logger.warning(f"Stem separation failed: {e}")
        import traceback
        traceback.print_exc()
        # Fallback to the original filter-based mixer with refinement loop
        from mixer import mix_set
        from quality_analyzer import run_refinement_loop, format_analysis_log
        progress(0.10, desc="Fallback: filter-based mixing with refinement...")
        set_audio, set_info, _ = run_refinement_loop(
            mix_fn=mix_set,
            tracks=app_state.analyses,
            order=app_state.set_order,
            transitions=app_state.transitions,
            max_iter=int(max_iter),
            progress_cb=lambda p, m: progress(0.10 + p * 0.80, desc=m)
        )
        method = f"Filter-based with {int(max_iter)} refinement iterations (demucs failed: {e})"

    app_state.rendered_set = set_audio

    progress(0.92, desc="Saving audio...")
    tmp = tempfile.NamedTemporaryFile(suffix='.wav', delete=False)
    audio_int16 = (set_audio.T * 32767).astype(np.int16)
    scipy.io.wavfile.write(tmp.name, sr, audio_int16)

    # Summary
    summary = f"# ✅ DJ Set Rendered\n\n"
    summary += f"- **Total duration:** {set_info.get('total_duration', 0):.1f}s "
    summary += f"({set_info.get('total_duration', 0)/60:.1f} min)\n"
    summary += f"- **Tracks:** {len(set_info.get('tracks', []))}\n"
    summary += f"- **Method:** {method}\n\n"

    summary += "## Tracklist\n"
    for i, t in enumerate(set_info.get('tracks', [])):
        fn = t.get('filename', '?')
        tl = t.get('tl_start', 0)
        stretch = t.get('stretch', 1.0)
        extra = f" (×{stretch:.3f})" if abs(stretch - 1.0) > 0.003 else ""
        summary += f"{i+1}. **{fn}** — starts at {tl:.0f}s{extra}\n"

    if set_info.get('transitions'):
        summary += "\n## Transitions\n"
        for t in set_info['transitions']:
            if isinstance(t, dict):
                summary += f"- {t}\n"
            else:
                summary += f"- {t}\n"

    return tmp.name, summary