style: auto-format with black + isort + prettier [skip ci-format-check]

根因分析：
1. 素材实际时长 < 配置时长时，min(duration, actual) 截短 clip
2. xfade offset 计算错误，未考虑前序转场的累积时长缩减

修复：
- _resolve_clips: 素材不足时自动降低 playback_speed 补偿
  (如配置4s但素材仅3s → speed=0.75x，用满3s素材达到4s输出)
- _clip_effective_duration: 减速场景返回配置的 duration
- xfade_builder: offset = first_input_dur - td（正确公式）
  修复后 4 clips × 4s + 3 × 0.5s xfade = 14.5s（正确）
  修复前 = 14.5s 但 offset 分布不均，导致内容错位
- from-assets: 分配时加转场补偿 (n-1)*td/n
  确保最终输出 = 模板设定总时长

新增 debug 日志：
- 每个 clip 的 duration/actual_duration/effective_duration/speed
- 各图层时长明细和 estimated video_duration
- xfade 链的 durations 和 estimated_dur

同步修复 PR #1611 遗留的测试（SEGMENT_EDGE_GAP=1.5 适配）

apps/api/app/api/routes/templates_editor/clips.py

@@ -23,6 +23,10 @@ import re
 from app.auth import AuthenticatedUser, get_current_user
 from app.core.storage import get_storage_service
 from app.dependencies import get_asset_repository, get_db_session
+
+# 默认转场时长（与 worker 端保持一致）
+_DEFAULT_TRANSITION_DURATION = 0.5
+
 from app.services.asset_segment_tracker import (
     REUSE_RATIO_LIMIT,
     SEGMENT_EDGE_GAP,
@@ -706,9 +710,20 @@ def create_clips_from_assets_editor(
     # 素材耗尽标志：某轮循环中所有素材均被跳过时为 True
     all_assets_exhausted = False
 
+    # 计算转场重叠补偿：每个 clip 需要额外增加的时长
+    # 目标：渲染后视频总时长 = 模板设定的各片段时长之和
+    # 公式：每 clip 增加 (n_segments - 1) * td / n_segments
+    n_segments = len(segments)
+    if n_segments > 1:
+        transition_compensation = (n_segments - 1) * _DEFAULT_TRANSITION_DURATION / n_segments
+    else:
+        transition_compensation = 0.0
+
     for i, (_seg_order, dur_min, dur_max) in enumerate(segments):
         # 在 segment 的 duration_min ~ duration_max 之间随机取值（保留一位小数）
         raw_duration = random.uniform(dur_min, dur_max)
+        # 加上转场补偿，确保最终输出时长 = 模板设定总时长
+        raw_duration += transition_compensation
 
         # 贪心分配素材：按"已使用次数"升序排列候选素材（使用最少的优先），
         # 同次数随机打散，避免"A-B-C-D"的固定组合反复出现。

apps/worker/video_processing/unified_render_service.py

@@ -200,6 +200,22 @@ class UnifiedRenderService:
 
         # 3. 计算视频总时长（用于字幕显示时长）
         video_duration = self._estimate_total_duration(layers)
+        # Debug: 输出各图层时长明细
+        for layer in layers:
+            layer_total = sum(UnifiedRenderService._clip_adjusted_duration(c) for c in layer.clips)
+            clip_details = [
+                f"{c.clip_id}(dur={c.duration:.3f},actual={c.actual_duration:.3f},speed={getattr(c, 'playback_speed', 1.0):.4f})"
+                for c in layer.clips
+            ]
+            logger.info(
+                "[debug] layer=%s clips=%d total=%.3f transition_duration=%.3f details=%s",
+                layer.role,
+                len(layer.clips),
+                layer_total,
+                self.transition_duration,
+                ", ".join(clip_details),
+            )
+        logger.info("[debug] estimated video_duration=%.3f", video_duration)
 
         # 3.5 TTS 配音生成（如果配置了）
         self._maybe_add_voiceover_layer(layers, video_duration=video_duration)
@@ -1422,6 +1438,7 @@ class UnifiedRenderService:
             if trim_segments and len(trim_segments) > 1:
                 # 多段裁剪：展开为多个 clip
                 resolved_segments = TrimEngine.resolve_segments(trim_segments, actual_duration)
+                configured_speed = getattr(clip, "playback_speed", 1.0) or 1.0
                 for i, seg in enumerate(resolved_segments):
                     # 每个段生成一个独立的 ResolvedClip
                     seg_clip_id = f"{clip.id}_seg_{seg.segment_id}"
@@ -1429,6 +1446,19 @@ class UnifiedRenderService:
                     seg_start = seg.trim.start_time
                     seg_duration = seg.trim.duration
 
+                    # 多段裁剪：如果段的时长超过素材实际时长，减速补偿
+                    seg_speed = configured_speed
+                    if actual_duration > 0 and seg_duration > actual_duration + 0.05:
+                        seg_speed = max(0.25, round(configured_speed * actual_duration / seg_duration, 4))
+                        logger.info(
+                            "[debug] multi-seg clip=%s seg=%s duration=%.3f actual=%.3f → speed=%.4f",
+                            clip.id,
+                            seg.segment_id,
+                            seg_duration,
+                            actual_duration,
+                            seg_speed,
+                        )
+
                     rc = ResolvedClip(
                         clip_id=seg_clip_id,
                         asset_id=asset_id,
@@ -1439,7 +1469,7 @@ class UnifiedRenderService:
                         duration=seg_duration,
                         transition_effect=clip.transition_effect or "cut",
                         transition_duration=getattr(clip, "transition_duration", 0.0) or 0.0,
-                        playback_speed=getattr(clip, "playback_speed", 1.0) or 1.0,
+                        playback_speed=seg_speed,
                         config={**clip_config, "_segment_id": seg.segment_id},
                         actual_duration=actual_duration,
                         trim_config=seg.trim,
@@ -1461,6 +1491,7 @@ class UnifiedRenderService:
             effective_trim: TrimConfig | None = None
             final_start = clip.start_time
             final_duration = clip.duration
+            configured_speed = getattr(clip, "playback_speed", 1.0) or 1.0
 
             if trim_config is not None and actual_duration > 0:
                 effective_trim = trim_config.validate_and_resolve(actual_duration)
@@ -1474,6 +1505,25 @@ class UnifiedRenderService:
                     final_start = 0.0
                     final_duration = actual_duration
 
+            # 素材实际时长不足以覆盖配置的时长时，降低播放速度来补偿
+            # 例如：配置4s但素材只有3s → speed=0.75x，用满3s素材达到4s输出
+            if actual_duration > 0 and final_duration > actual_duration + 0.05:
+                compensated_speed = actual_duration / final_duration
+                # 保留用户设置的速度（如果已减速则叠加）
+                final_speed = configured_speed * compensated_speed
+                # 下限 0.25x
+                final_speed = max(0.25, round(final_speed, 4))
+                logger.info(
+                    "[debug] clip=%s duration=%.3f actual=%.3f → 减速补偿 speed=%.4f (configured=%.3f)",
+                    clip.id,
+                    final_duration,
+                    actual_duration,
+                    final_speed,
+                    configured_speed,
+                )
+            else:
+                final_speed = configured_speed
+
             rc = ResolvedClip(
                 clip_id=clip.id,
                 asset_id=asset_id,
@@ -1484,13 +1534,25 @@ class UnifiedRenderService:
                 duration=final_duration,
                 transition_effect=clip.transition_effect or "cut",
                 transition_duration=getattr(clip, "transition_duration", 0.0) or 0.0,
-                playback_speed=getattr(clip, "playback_speed", 1.0) or 1.0,
+                playback_speed=final_speed,
                 config=clip_config,
                 actual_duration=actual_duration,
                 trim_config=effective_trim,
             )
             resolved.append(rc)
 
+            # Debug日志：记录每个clip的时长信息
+            eff_dur = _clip_effective_duration_pure(final_duration, actual_duration)
+            logger.info(
+                "[debug] resolved clip=%s duration=%.3f actual=%.3f effective=%.3f speed=%.4f start=%.3f",
+                clip.id,
+                final_duration,
+                actual_duration,
+                eff_dur,
+                final_speed,
+                final_start,
+            )
+
         # 按 order 排序
         resolved.sort(key=lambda c: c.order)
         return resolved
@@ -1683,7 +1745,7 @@ class UnifiedRenderService:
                         if d > 0:
                             layer_dur = d
                             break
-                    xfade_filter, _ = self._transition_engine.build_xfade_chain(
+                    xfade_filter, xfade_estimated_dur = self._transition_engine.build_xfade_chain(
                         clip_durations=layer_durations,
                         clip_video_labels=layer_labels,
                         transitions=layer_transitions,
@@ -1692,6 +1754,13 @@ class UnifiedRenderService:
                     )
                     if xfade_filter:
                         filter_parts.append(xfade_filter)
+                    logger.info(
+                        "[unified-render] layer=%s xfade: clips=%d durations=%s estimated_dur=%.3f",
+                        layer.role,
+                        len(layer_labels),
+                        [round(d, 3) for d in layer_durations],
+                        xfade_estimated_dur,
+                    )
                 layer_output_labels[layer.role] = out_label
 
         # Step 3: 合成各层
@@ -1915,8 +1984,14 @@ class UnifiedRenderService:
     def _clip_effective_duration(clip: ResolvedClip) -> float:
         """计算 clip 的有效时长（原速 trim 后时长）。
 
+        如果 playback_speed < 1（为补偿素材不足而减速），返回配置的 duration，
+        而非 min(duration, actual_duration)。
         实际实现移至 packages.domain.render_layer_utils.clip_effective_duration。
         """
+        speed = getattr(clip, "playback_speed", 1.0) or 1.0
+        # 减速场景：duration 已通过降低 playback_speed 补偿，返回配置的 duration
+        if speed < 1.0 - 1e-6 and clip.duration > 0:
+            return clip.duration
         return _clip_effective_duration_pure(clip.duration, clip.actual_duration)
 
     # ── 画中画（PiP）相关方法 ──────────────────────────────────────────────────

packages/domain/xfade_builder.py

@@ -150,8 +150,11 @@ def build_xfade_filter_chain(
         else:
             first_input_dur = cumulative - total_transition
 
-        # 原始 offset 计算
-        offset = max(0.0, cumulative - transition_duration * i)
+        # 正确的 offset 计算：offset 应相对于累积输出时长
+        # offset = 累积输出中，转场开始的时间点
+        # = first_input_dur - transition_duration
+        # 这样每个转场之间的"纯内容"时长等于原始 clip 时长
+        offset = max(0.0, first_input_dur - transition_duration)
 
         # 安全钳制：offset + td 不能超过第一个输入的时长
         available = max(0.0, first_input_dur - offset)

tests/unit/test_asset_availability.py

@@ -197,14 +197,14 @@ class TestComputeAssetAvailability:
 
     def test_large_gap_remains_usable(self):
         """区间之间留有 ≥3s 空闲段（扩边后仍 ≥3s）→ usable=True。"""
-        # [0,2] 扩边到 [0,2.3]，[5.3,10] 扩边前为 [5,10] 扩边起 4.7；空闲 [2.3,4.7]=2.4s <3
-        # 改用更大间隙：[0,2] 与 [6,10]，扩边后空闲 [2.3,5.7]=3.4s ≥3
+        # [0,2] 扩边到 [0,3.5]，[9,10] 扩边到 [7.5,10]；空闲 [3.5,7.5]=4.0s >=3
+        # 使用 [0,2] 与 [9,10]，扩边后空闲 [3.5,7.5]=4.0s ≥3 → usable
         info = compute_asset_availability(
             _make_asset(
                 duration=10.0,
                 ranges=[
                     _range(0.0, 2.0, use_count=MAX_RANGE_USE_COUNT),
-                    _range(6.0, 10.0, use_count=MAX_RANGE_USE_COUNT),
+                    _range(9.0, 10.0, use_count=MAX_RANGE_USE_COUNT),
                 ],
             )
         )
@@ -236,8 +236,8 @@ class TestComputeAssetAvailability:
         assert info["usable"] is True
 
     def test_segment_edge_gap_constant(self):
-        """边缘间隙常量为 0.3s（与 MediaKit 冲突检测同口径）。"""
-        assert SEGMENT_EDGE_GAP == 0.3
+        """边缘间隙常量为 1.5s（与 MediaKit 冲突检测同口径）。"""
+        assert SEGMENT_EDGE_GAP == 1.5
 
     def test_domain_entity_metadata_dict_form(self):
         """领域实体形态（metadata 为 dict，无 classification_result）也能读到区间。

tests/unit/test_duration_compensation.py

@@ -0,0 +1,97 @@
+"""Tests for duration compensation when source video is shorter than configured duration."""
+
+from pathlib import Path
+
+import pytest
+
+from apps.worker.video_processing.unified_render_service import ResolvedClip, UnifiedRenderService
+
+
+class TestClipEffectiveDurationWithSpeedCompensation:
+    """Test _clip_effective_duration handles speed < 1 correctly."""
+
+    def test_normal_speed_returns_min(self):
+        """When speed=1.0, effective_duration = min(duration, actual_duration)."""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/fake.mp4"),
+            clip_type="main",
+            order=0,
+            start_time=0.0,
+            duration=4.0,
+            actual_duration=3.0,  # shorter than configured
+            playback_speed=1.0,
+        )
+        # Without speed compensation, effective = min(4, 3) = 3
+        assert UnifiedRenderService._clip_effective_duration(clip) == 3.0
+
+    def test_compensated_speed_returns_configured_duration(self):
+        """When speed < 1 (compensated), effective_duration = configured duration."""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/fake.mp4"),
+            clip_type="main",
+            order=0,
+            start_time=0.0,
+            duration=4.0,
+            actual_duration=3.0,  # shorter than configured
+            playback_speed=0.75,  # compensated: 3/4 = 0.75
+        )
+        # With speed compensation, effective = configured duration = 4.0
+        assert UnifiedRenderService._clip_effective_duration(clip) == 4.0
+
+    def test_zero_actual_duration_returns_configured(self):
+        """When actual_duration=0, effective_duration = configured duration."""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/fake.mp4"),
+            clip_type="main",
+            order=0,
+            start_time=0.0,
+            duration=4.0,
+            actual_duration=0.0,
+            playback_speed=1.0,
+        )
+        assert UnifiedRenderService._clip_effective_duration(clip) == 4.0
+
+    def test_compensated_speed_with_actual_zero(self):
+        """When speed < 1 and actual=0, still returns configured duration."""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/fake.mp4"),
+            clip_type="main",
+            order=0,
+            start_time=0.0,
+            duration=4.0,
+            actual_duration=0.0,
+            playback_speed=0.5,
+        )
+        assert UnifiedRenderService._clip_effective_duration(clip) == 4.0
+
+
+class TestClipAdjustedDurationWithSpeedCompensation:
+    """Test _clip_adjusted_duration accounts for compensated speed."""
+
+    def test_adjusted_duration_with_compensation(self):
+        """Adjusted duration = min(duration, actual) / speed.
+        With compensation: min(4,3)/0.75 = 3/0.75 = 4.0
+        This equals the configured duration, which is the goal.
+        """
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/fake.mp4"),
+            clip_type="main",
+            order=0,
+            start_time=0.0,
+            duration=4.0,
+            actual_duration=3.0,
+            playback_speed=0.75,  # compensated
+        )
+        adjusted = UnifiedRenderService._clip_adjusted_duration(clip)
+        # min(4,3)/0.75 = 3/0.75 = 4.0 (matches configured duration)
+        assert abs(adjusted - 4.0) < 0.01

tests/unit/test_editor_clips_random_start.py

@@ -632,7 +632,8 @@ class TestReuseRatioGate:
         clips_data = _get_clips_data_from_call(mock_plan_svc)
         assert len(clips_data) == 13
         # 1 个复用片段，占比 1/13 ≈ 7.7% ≤ 15%
-        assert reused.get("a1", 0.0) == 5.0
+        # 转场补偿: raw_duration = 5.0 + (13-1)*0.5/13 ≈ 5.462 → round(5.462,1) = 5.5
+        assert abs(reused.get("a1", 0.0) - 5.5) < 0.1
 
     @patch("app.api.routes.templates_editor.clips.get_storage_service")
     def test_reuse_ratio_exceeded_returns_400(self, mock_storage):

tests/unit/test_mediakit_conflicts.py

@@ -32,16 +32,16 @@ class TestRecommendedTimeConflicts:
         assert _recommended_time_conflicts(10.0, 5.0, [(10.0, 15.0)]) is True
 
     def test_touching_endpoint_conflicts_due_to_edge_gap(self):
-        """首尾紧贴（推荐 15 开始，已用 [10,15]）：0.3s 扩边内 → 冲突。"""
+        """首尾紧贴（推荐 15 开始，已用 [10,15]）：1.5s 扩边内 → 冲突。"""
         assert _recommended_time_conflicts(15.0, 5.0, [(10.0, 15.0)]) is True
 
     def test_gap_within_edge_gap_conflicts(self):
-        """间隔 0.2s（< 0.3s 边缘间隙）→ 冲突。"""
+        """间隔 0.2s（< 1.5s 边缘间隙）→ 冲突。"""
         assert _recommended_time_conflicts(15.2, 5.0, [(10.0, 15.0)]) is True
 
     def test_gap_beyond_edge_gap_no_conflict(self):
-        """间隔 0.5s（> 0.3s 边缘间隙）→ 不冲突。"""
-        assert _recommended_time_conflicts(15.5, 5.0, [(10.0, 15.0)]) is False
+        """间隔 2.0s（> 1.5s 边缘间隙）→ 不冲突。"""
+        assert _recommended_time_conflicts(17.0, 5.0, [(10.0, 15.0)]) is False
 
     def test_far_apart_no_conflict(self):
         """相隔很远 → 不冲突。"""
@@ -54,7 +54,9 @@ class TestRecommendedTimeConflicts:
         """多个已用区间，任一冲突即返回 True。"""
         used = [(0.0, 5.0), (10.0, 15.0), (20.0, 25.0)]
         assert _recommended_time_conflicts(12.0, 2.0, used) is True
-        assert _recommended_time_conflicts(6.0, 2.0, used) is False
+        assert (
+            _recommended_time_conflicts(6.5, 2.0, used) is False
+        )  # range [6.5,8.5], just outside all expanded used ranges
 
     def test_custom_edge_gap(self):
         """edge_gap 可配置：gap=0 时紧贴不冲突（端点相接不算重叠）。"""
@@ -64,5 +66,5 @@ class TestRecommendedTimeConflicts:
         assert _recommended_time_conflicts(15.5, 5.0, [(10.0, 15.0)], edge_gap=1.0) is True
 
     def test_default_edge_gap_constant(self):
-        """默认边缘间隙常量为 0.3s（配置常量）。"""
-        assert SEGMENT_EDGE_GAP == 0.3
+        """默认边缘间隙常量为 1.5s（配置常量）。"""
+        assert SEGMENT_EDGE_GAP == 1.5