deploy: piano-roll notes output (runtime files only)

app.py

@@ -5,6 +5,7 @@ separation stage is GPU-relevant, so it alone is wrapped with @spaces.GPU
 (a no-op everywhere else).
 """
 
+import json
 import os
 import tempfile
 from pathlib import Path
@@ -104,7 +105,13 @@ def flip(audio_path, model, progress=gr.Progress()):
         else None
         for name in PREVIEW_STEMS
     ]
-    return str(result["zip_path"]), summary, *previews
+
+    # Per-stem detected notes for the client piano-roll (appended LAST so the preview
+    # output indices above stay stable for existing API callers).
+    notes_path = bundle / "notes.json"
+    notes = json.loads(notes_path.read_text()) if notes_path.exists() else {"stems": {}}
+
+    return str(result["zip_path"]), summary, *previews, notes
 
 
 with gr.Blocks(title="StemFlipper") as demo:
@@ -125,10 +132,13 @@ with gr.Blocks(title="StemFlipper") as demo:
         preview_outs = [
             gr.Audio(label=name, interactive=False) for name in PREVIEW_STEMS
         ]
+    # Per-stem detected notes → the static web frontend draws piano-rolls from this.
+    # Hidden in the Gradio UI itself (visible=False) but present in the API output.
+    notes_out = gr.JSON(visible=False)
     go_btn.click(
         flip,
         inputs=[audio_in, model_in],
-        outputs=[zip_out, summary_out, *preview_outs],
+        outputs=[zip_out, summary_out, *preview_outs, notes_out],
         api_name="flip",
     )
 

stemflipper/export.py

@@ -135,6 +135,33 @@ def write_rpp(
     return path
 
 
+def write_notes(tracks: dict, duration: float, bundle_dir: str | Path) -> Path:
+    """Per-stem detected notes → notes.json, for UI piano-rolls (and the download).
+
+    tracks: {stem_name: {"notes": [{pitch,start,end,velocity}], "is_drum": bool}}.
+    Each stem's notes are stored as compact ``[pitch, start, end, velocity]`` rows
+    (ints/rounded floats) so the file stays small and a client can draw them without
+    parsing MIDI. ``duration`` bounds the time axis. Stems with no notes are omitted.
+    """
+    stems = {}
+    for name, data in tracks.items():
+        notes = data.get("notes") or []
+        if not notes:
+            continue
+        stems[name] = {
+            "is_drum": bool(data.get("is_drum")),
+            "notes": [
+                [int(n["pitch"]), round(float(n["start"]), 4),
+                 round(float(n["end"]), 4), int(n.get("velocity", 100))]
+                for n in notes
+            ],
+        }
+    payload = {"duration": round(float(duration), 3), "stems": stems}
+    path = Path(bundle_dir) / "notes.json"
+    path.write_text(json.dumps(payload))
+    return path
+
+
 def write_manifest(bundle_dir: str | Path, meta: dict) -> Path:
     path = Path(bundle_dir) / "manifest.json"
     path.write_text(json.dumps(meta, indent=2))

stemflipper/pipeline.py

@@ -142,6 +142,9 @@ def run_pipeline(
 
     report(0.9, "Writing MIDI, manifest, Reaper project")
     export.write_midi(tracks, analysis.tempo, bundle_dir / "midi")
+    export.write_notes(tracks, analysis.duration, bundle_dir)
+    for name, meta in stems_meta.items():
+        meta["notes"] = "notes.json" if tracks.get(name, {}).get("notes") else None
     manifest = export.make_manifest_meta(input_path.name, analysis, model, stems_meta)
     export.write_manifest(bundle_dir, manifest)
     export.write_readme(bundle_dir, input_path.name, analysis)