fix(audio): offline mix limiter -3dBFS, 2-stage normalize (-14 LUFS + hard peak -1 dBTP), OGG export

app/core/render_engine.py

@@ -223,6 +223,33 @@ def _apply_limiter(buf, params, sr):
     x = np.clip(buf, -1.0, 1.0)
     return np.tanh(x * k) / tanh_k
 
+def _apply_mix_limiter(buf, sr):
+    """Mixer summing cap (spec §2): smoothed brickwall -3 dBFS mirror C++
+    realtime (NativeInstrumentEngine.cpp renderAll) — ceiling 0.7071, attack
+    0.1 (~10 samples), release 0.0006, gain chung 2 kênh. Áp cho MASTER CHAIN
+    INPUT offline (realtime đã cap sau khi sum; offline trước đây thiếu).
+    ponytail: loop Python O(n) — thay numba/vectorized khi render >10 phút."""
+    if buf.size == 0:
+        return buf
+    k_ceil = 0.7071
+    k_attack = 0.1
+    k_release = 0.0006
+    eps = 1e-12
+    m_list = np.max(np.abs(buf), axis=0).tolist()
+    n = buf.shape[1]
+    g = 1.0
+    gains = np.empty(n, dtype=np.float32)
+    for i in range(n):
+        t = k_ceil / (m_list[i] + eps)
+        if t > 1.0:
+            t = 1.0
+        if t < g:
+            g += (t - g) * k_attack
+        else:
+            g += (1.0 - g) * k_release
+        gains[i] = g
+    return buf * gains
+
 def _apply_exciter(buf, params, sr):
     params = params or {}
     drive = float(params.get("drive", 40) or 40)
@@ -862,6 +889,11 @@ class PythonRenderEngine:
                 _cache={},
             )
 
+            # Mixer summing cap (spec §2): -3 dBFS brickwall mirror C++ realtime —
+            # áp cho MASTER CHAIN INPUT, TRƯỚC master FX chain/volume. Offline
+            # trước đây thiếu cap này (chỉ anti-clip >1.0 sau master chain).
+            master_buffer = _apply_mix_limiter(master_buffer, self.sample_rate)
+
             # Masterbus FX chain (VST3 FX / builtin) — render qua native_bridge
             # --render-fx, rồi volume_db master; backward compatible (không có
             # master.fx_chain → giữ nguyên luồng cũ).
@@ -948,16 +980,29 @@ class PythonRenderEngine:
             if normalize:
                 from app.core import loudness
                 if normalize_target == "-14lufs":
+                    # Spec: master ra -14 LUFS (scale toàn cục) VÀ hard-peak
+                    # <= -1.0 dBTP (chặn peak sau scale, deterministic — peak
+                    # cap thắng khi nguồn crest cao, LUFS hạ xuống dưới -14).
+                    # ponytail: lookahead limiter khi cần giữ -14 LUFS với
+                    # nguồn crest cao (master thật hiếm gặp).
                     _l = loudness.integrated_lufs(master_buffer, out_sr)
                     if np.isfinite(_l):
                         master_buffer *= 10 ** ((-14.0 - _l) / 20.0)
+                    _tp = loudness.true_peak_db(master_buffer, out_sr)
+                    if np.isfinite(_tp) and _tp > -1.0:
+                        master_buffer *= 10 ** ((-1.0 - _tp) / 20.0)
                 else:  # "-1dbtp"
                     _tp = loudness.true_peak_db(master_buffer, out_sr)
                     if np.isfinite(_tp):
                         master_buffer *= 10 ** ((-1.0 - _tp) / 20.0)
 
-            # Write final output file (D3: PCM_16/PCM_24 + dither, FLOAT mac dinh)
-            if bit_depth == 16:
+            # Write final output file (D3: PCM_16/PCM_24 + dither, FLOAT mac dinh).
+            # OGG: Vorbis float lossy — bỏ dither/PCM/BWF (chunk WAV-only).
+            ext = os.path.splitext(output_filepath)[1].lower()
+            if ext == ".ogg":
+                sf.write(output_filepath, master_buffer.T, out_sr,
+                         format="OGG", subtype="VORBIS")
+            elif bit_depth == 16:
                 sf.write(output_filepath, _quantize_pcm(master_buffer, 16, dither).T,
                          out_sr, subtype="PCM_16")
             elif bit_depth == 24:
@@ -967,7 +1012,7 @@ class PythonRenderEngine:
                 sf.write(output_filepath, master_buffer.T, out_sr, subtype="FLOAT")
             # Gap 13: BWF/INFO chunks (bext + LIST/INFO title/artist/ISRC) —
             # chen sau khi ghi PCM, loi metadata khong lam hong file audio.
-            if metadata:
+            if metadata and ext != ".ogg":
                 try:
                     from app.core.wav_bwf import patch_bwf_metadata
                     patch_bwf_metadata(output_filepath, metadata)