Prioritize repeated chorus-like regions in music crop selection

Constraint: Music retrieval should sample repeated hook-like regions without adding heavyweight structure models or breaking the existing lightweight candidate stack
Rejected: Reserve repeated-section logic for a later dedicated chorus detector | delays a practical chorus-like signal that can already improve query realism today
Confidence: medium
Scope-risk: moderate
Directive: Treat repeated_section_aware as a lightweight chorus proxy; future chorus ranking should refine rather than discard these candidates
Tested: /usr/local/miniconda3/bin/python -m py_compile acr-engine/src/data/dataset.py acr-engine/src/data/manifest_tools.py acr-engine/train.py acr-engine/src/data/external_adapters.py; synthetic_v2 dry-run with --segment-strategy repeated_section_aware; handcrafted 24s repeated-motif fixture with repeated_section_aware and hybrid offset checks
Not-tested: Full end-to-end metric impact on FMA/internal datasets with repeated_section_aware enabled

@@ -95,6 +95,32 @@ def compute_candidate_offsets(
         step = max(1, len(offsets) // 8)
         return sorted(set(offsets[::step][:8]))
 
+    if strategy == "repeated_section_aware":
+        hop = max(segment_len // 2, 1)
+        starts = list(range(0, max(len(y) - segment_len + 1, 1), hop))
+        if len(starts) < 2:
+            return starts[:1]
+        feats = []
+        for start in starts:
+            seg = y[start : start + segment_len]
+            if len(seg) < segment_len:
+                seg = np.pad(seg, (0, segment_len - len(seg)))
+            chroma = librosa.feature.chroma_cqt(y=seg, sr=sr)
+            feat = np.mean(chroma, axis=1)
+            norm = float(np.linalg.norm(feat) + 1e-12)
+            feats.append(feat / norm)
+        scores: List[tuple[float, int]] = []
+        for i, feat in enumerate(feats):
+            sims = []
+            for j, other in enumerate(feats):
+                if i == j:
+                    continue
+                sims.append(float(np.dot(feat, other)))
+            repeat_score = max(sims) if sims else 0.0
+            scores.append((repeat_score, starts[i]))
+        scores.sort(key=lambda x: x[0], reverse=True)
+        return sorted(set(start for _, start in scores[: min(6, len(scores))]))
+
     return []
 
 
@@ -186,7 +212,7 @@ class ACRDataset(Dataset):
 
         if self.segment_strategy == "hybrid":
             candidate_pool: List[int] = []
-            for strategy in ("beat_aware", "high_energy", "onset_aware", "silence_aware"):
+            for strategy in ("repeated_section_aware", "beat_aware", "high_energy", "onset_aware", "silence_aware"):
                 candidate_pool.extend(
                     compute_candidate_offsets(
                         y=y,
@@ -365,7 +391,7 @@ class SongPairDataset(Dataset):
                     offset = min(random.choice(direct_candidates) / self.sr, max_offset)
                 elif self.segment_strategy == "hybrid":
                     candidate_pool: List[int] = []
-                    for strategy in ("beat_aware", "high_energy", "onset_aware", "silence_aware"):
+                    for strategy in ("repeated_section_aware", "beat_aware", "high_energy", "onset_aware", "silence_aware"):
                         candidate_pool.extend(
                             compute_candidate_offsets(
                                 y=full_y,

@@ -516,7 +516,7 @@ def main():
     p.add_argument("--eval-ratio", type=float, default=0.2)
     p.add_argument("--query-duration", type=float, default=8.0)
     p.add_argument("--query-stride", type=float, default=None)
-    p.add_argument("--query-strategy", choices=["random", "sliding", "silence_aware", "high_energy", "onset_aware", "beat_aware", "hybrid"], default="random")
+    p.add_argument("--query-strategy", choices=["random", "sliding", "silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware", "hybrid"], default="random")
     p.add_argument("--silence-top-db", type=int, default=30)
     p.add_argument("--seed", type=int, default=42)
 
@@ -548,8 +548,8 @@ def main():
     p.add_argument("--eval-ratio", type=float, default=0.2)
     p.add_argument("--query-duration", type=float, default=8.0)
     p.add_argument("--query-stride", type=float, default=None)
-    p.add_argument("--query-strategy", choices=["random", "sliding", "silence_aware", "high_energy", "onset_aware", "beat_aware", "hybrid"], default="random")
-    p.add_argument("--segment-strategy", choices=["random", "silence_aware", "high_energy", "onset_aware", "beat_aware", "hybrid"], default="random")
+    p.add_argument("--query-strategy", choices=["random", "sliding", "silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware", "hybrid"], default="random")
+    p.add_argument("--segment-strategy", choices=["random", "silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware", "hybrid"], default="random")
     p.add_argument("--silence-top-db", type=int, default=30)
     p.add_argument("--index-checkpoint-every-refs", type=int, default=100)
     p.add_argument("--seed", type=int, default=42)

@@ -117,14 +117,14 @@ def build_train_eval_from_audio_dir(
 
         if duration >= query_duration:
             strategy_offsets = []
-            if query_strategy in {"silence_aware", "high_energy", "onset_aware", "beat_aware"}:
+            if query_strategy in {"silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware"}:
                 strategy_offsets = compute_strategy_offsets(path, duration, query_strategy)
             elif query_strategy == "hybrid":
-                for strategy in ("beat_aware", "high_energy", "onset_aware", "silence_aware"):
+                for strategy in ("repeated_section_aware", "beat_aware", "high_energy", "onset_aware", "silence_aware"):
                     strategy_offsets.extend(compute_strategy_offsets(path, duration, strategy))
                 strategy_offsets = sorted(set(strategy_offsets))
 
-            if query_strategy in {"silence_aware", "high_energy", "onset_aware", "beat_aware"} and strategy_offsets:
+            if query_strategy in {"silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware"} and strategy_offsets:
                 offsets = strategy_offsets
             elif query_strategy == "hybrid" and strategy_offsets:
                 if query_stride and query_stride > 0:
@@ -277,7 +277,7 @@ def main():
     p.add_argument("--eval-ratio", type=float, default=0.2)
     p.add_argument("--query-duration", type=float, default=8.0)
     p.add_argument("--query-stride", type=float, default=None)
-    p.add_argument("--query-strategy", choices=["random", "sliding", "silence_aware", "high_energy", "onset_aware", "beat_aware", "hybrid"], default="random")
+    p.add_argument("--query-strategy", choices=["random", "sliding", "silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware", "hybrid"], default="random")
     p.add_argument("--silence-top-db", type=int, default=30)
     p.add_argument("--seed", type=int, default=42)
 

@@ -125,7 +125,7 @@ def main():
     parser.add_argument("--epochs", type=int, default=None)
     parser.add_argument("--batch-size", type=int, default=None)
     parser.add_argument("--lr", type=float, default=None)
-    parser.add_argument("--segment-strategy", choices=["random", "silence_aware", "high_energy", "onset_aware", "beat_aware", "hybrid"], default="random")
+    parser.add_argument("--segment-strategy", choices=["random", "silence_aware", "high_energy", "onset_aware", "beat_aware", "repeated_section_aware", "hybrid"], default="random")
     parser.add_argument("--silence-top-db", type=int, default=30)
     parser.add_argument("--dry-run", action="store_true")
     args = parser.parse_args()

@@ -5618,3 +5618,60 @@
 - 下一步可继续叠加：
   - repeated-section-aware
   - chorus-like candidate mining
+
+### Stage: repeated-section-aware / chorus-like candidate sampling
+
+完成项：
+- 在 `acr-engine/src/data/dataset.py` 新增：
+  - `repeated_section_aware`
+- 在 `acr-engine/src/data/manifest_tools.py` 新增：
+  - `--query-strategy repeated_section_aware`
+- 在 `train.py` 与 `external_adapters.py` 暴露：
+  - `repeated_section_aware`
+- 实现方式：
+  - 对滑窗片段提取 `chroma_cqt`
+  - 取窗口级平均 chroma 向量
+  - 计算窗口间相似度
+  - 优先选择“与其它窗口最相似”的片段，作为重复主段 / 副歌 hook 的轻量近似
+- 将 `hybrid` 扩展为优先复用：
+  - `repeated_section_aware`
+  - `beat_aware`
+  - `high_energy`
+  - `onset_aware`
+  - `silence_aware`
+
+验证结果：
+- 编译验证：
+  - `/usr/local/miniconda3/bin/python -m py_compile src/data/dataset.py src/data/manifest_tools.py train.py src/data/external_adapters.py`
+- 人造“重复副歌”音频验证：
+  - 构造 `24s` 音频
+  - `8-12s` 与 `16-20s` 放置两段重复 motif
+- 直接重复候选结果：
+  - `DIRECT_REPEAT_CANDIDATES_SEC`：
+    - `6.0, 8.0, 10.0, 14.0, 16.0, 18.0`
+- query 生成结果：
+  - `REPEAT_QUERY_OFFSETS`：
+    - `6.0, 10.0, 14.0, 16.0, 18.0`
+  - `HYBRID_QUERY_OFFSETS`：
+    - `2.016, 2.048, 2.08, 6.0, 6.048, 8.0, 8.064, 10.0, 12.789, 14.0, 15.968, 16.0`
+- 训练侧偏移验证：
+  - `TRAIN_REPEAT_OFFSETS`：
+    - `17.5, 0.0, 0.0, 17.5, 7.5, 2.5`
+  - `TRAIN_HYBRID_OFFSETS`：
+    - `0.0, 8.032, 2.5, 2.048, 2.016, 7.5`
+  - 说明 repeated-section-aware 已能明显偏向重复主段周边，而 hybrid 也已吸收这类候选
+- dry-run 验证：
+  - `train.py --data data/synthetic_v2 --dry-run --segment-strategy repeated_section_aware`
+  - forward/backward 成功，`Embedding shape: torch.Size([64, 192])`
+
+结论：
+- 当前项目的音乐感知切片已经从：
+  - 避静音
+  - 高能区
+  - 起音点
+  - 拍点
+  进一步扩展到：
+  - **重复主段 / 近似副歌**
+- 下一步可继续做更强的：
+  - chorus-like multi-feature ranking
+  - 小规模真实数据策略 A/B 对比

@@ -357,12 +357,13 @@ flowchart TD
 | `high_energy` | 训练 query / 外部 query 生成 | 优先抽取 RMS 高能区，更接近副歌/主唱/强节奏段 | 是 |
 | `onset_aware` | 训练 query / 外部 query 生成 | 优先靠近起音事件，减少截到拖尾/空拍 | 是 |
 | `beat_aware` | 训练 query / 外部 query 生成 | 优先靠近节拍点，适合强节奏流行/电子/舞曲等 | 是 |
+| `repeated_section_aware` | 训练 query / 外部 query 生成 | 优先抽取与其它窗口最相似的重复主段，近似副歌/重复 hook | 是 |
 | `hybrid` | 训练 query / 外部 query 生成 | 混合 silence-aware + random，兼顾稳定性与泛化 | 是 |
 
 推荐理解：
 
 1. **训练不是全部随机切**  
-   当前训练集可用 `random / silence_aware / high_energy / onset_aware / beat_aware / hybrid`
+   当前训练集可用 `random / silence_aware / high_energy / onset_aware / beat_aware / repeated_section_aware / hybrid`
 2. **reference 建库不是随机切**  
    建库仍然是固定滑窗
 3. **外部数据 query 生成也不是只能随机切**  
@@ -390,6 +391,7 @@ flowchart TD
 - 更想贴近副歌/强节奏：`high_energy`
 - 更想贴近短音起点/打点：`onset_aware`
 - 更想贴近稳定节拍网格：`beat_aware`
+- 更想贴近副歌/重复 hook：`repeated_section_aware`
 
 ### 外部数据 query 生成推荐
 
@@ -412,6 +414,7 @@ flowchart TD
 | 更想贴近副歌/主段 | `high_energy` |
 | 更想贴近打点/起唱点 | `onset_aware` |
 | 更想贴近规则拍点/律动骨架 | `beat_aware` |
+| 更想贴近重复主段/副歌 hook | `repeated_section_aware` |
 | 既要音乐感知，又要保留泛化 | `hybrid` |
 
 ---