diff --git a/apps/worker/video_processing/unified_render_service.py b/apps/worker/video_processing/unified_render_service.py
old mode 100644
new mode 100755
index a01c42c7e..0235e65a8
--- a/apps/worker/video_processing/unified_render_service.py
+++ b/apps/worker/video_processing/unified_render_service.py
@@ -339,8 +339,8 @@ class UnifiedRenderService:
                 )
                 filters.append(f"pad={self.output_width}:{self.output_height}" ":(ow-iw)/2:(oh-ih)/2:black")
 
-            filters.append(f"fps={self.output_fps}")
             filters.append("setpts=PTS-STARTPTS")
+            filters.append(f"fps={self.output_fps}")
 
             filter_str = f"[{i}:v]{','.join(filters)}[{label}]"
             filter_parts.append(filter_str)
diff --git a/tests/unit/test_unified_render_service.py b/tests/unit/test_unified_render_service.py
old mode 100644
new mode 100755
index 4670c132b..8cae2ad27
--- a/tests/unit/test_unified_render_service.py
+++ b/tests/unit/test_unified_render_service.py
@@ -356,6 +356,89 @@ class TestBuildFilterComplex:
         assert "overlay=" in fc
         assert "[final_video]" in fc
 
+    def test_setpts_before_fps_in_xfade_inputs(self):
+        """多视频 xfade 模式：setpts=PTS-STARTPTS 必须在 fps 之前，确保 xfade 时各片段 PTS 一致。
+
+        构造两个不同时长的视频片段，验证生成的 filter_complex 中每个片段的
+        预处理滤镜链里 setpts 都在 fps 前面。
+        """
+        clips = [
+            _make_clip("c1", "main", order=0, duration=3.0),
+            _make_clip("c2", "main", order=1, duration=5.0),
+        ]
+        asset_paths = {
+            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+        }
+        svc = _make_service(clips, asset_paths)
+
+        with _patch_path_exists(), patch("video_processing.unified_render_service.probe_duration", return_value=5.0):
+            resolved = svc._resolve_clips()
+            layers = svc._group_clips_into_layers(resolved)
+            fc, _ = svc._build_filter_complex(layers)
+
+        # 确保 xfade 存在
+        assert "xfade=" in fc
+
+        # 提取每个 clip 的预处理滤镜链（[i:v]...[vi] 部分）
+        # 验证：每个 clip 滤镜链中，setpts=PTS-STARTPTS 的最后一次出现
+        # 必须在 fps= 的前面（PTS 归一化后再统一帧率）
+        import re
+
+        clip_pattern = re.compile(r"\[(\d+):v\](.+?)\[v\d+\]")
+        matches = clip_pattern.findall(fc)
+        assert len(matches) == 2, f"Expected 2 clip preprocessing chains, got {len(matches)}"
+
+        for idx, chain_str in matches:
+            # 找到所有 setpts 和 fps 的位置
+            setpts_positions = [m.start() for m in re.finditer(r"setpts=PTS-STARTPTS", chain_str)]
+            fps_positions = [m.start() for m in re.finditer(r"fps=\d+", chain_str)]
+
+            assert setpts_positions, f"clip {idx}: 未找到 setpts=PTS-STARTPTS"
+            assert fps_positions, f"clip {idx}: 未找到 fps="
+
+            # 最后一个 setpts 必须在第一个 fps 之前
+            last_setpts = max(setpts_positions)
+            first_fps = min(fps_positions)
+            assert last_setpts < first_fps, (
+                f"clip {idx}: setpts(position={last_setpts}) 应该在 fps(position={first_fps}) 之前。"
+                f"滤镜链: {chain_str}"
+            )
+
+    def test_setpts_before_fps_single_clip(self):
+        """单视频模式（一镜到底）：setpts 也必须在 fps 之前。
+
+        单视频虽然没有 xfade，但滤镜链顺序应保持一致，确保 PTS 处理逻辑统一。
+        """
+        clips = [_make_clip("c1", "main", order=0, duration=5.0)]
+        asset_paths = {"asset_c1.mp4": Path("/tmp/asset_c1.mp4")}
+        svc = _make_service(clips, asset_paths)
+
+        with _patch_path_exists(), patch("video_processing.unified_render_service.probe_duration", return_value=5.0):
+            resolved = svc._resolve_clips()
+            layers = svc._group_clips_into_layers(resolved)
+            fc, _ = svc._build_filter_complex(layers)
+
+        import re
+
+        clip_pattern = re.compile(r"\[(\d+):v\](.+?)\[v\d+\]")
+        matches = clip_pattern.findall(fc)
+        assert len(matches) == 1
+
+        chain_str = matches[0][1]
+        setpts_positions = [m.start() for m in re.finditer(r"setpts=PTS-STARTPTS", chain_str)]
+        fps_positions = [m.start() for m in re.finditer(r"fps=\d+", chain_str)]
+
+        assert setpts_positions, "单视频: 未找到 setpts=PTS-STARTPTS"
+        assert fps_positions, "单视频: 未找到 fps="
+
+        last_setpts = max(setpts_positions)
+        first_fps = min(fps_positions)
+        assert last_setpts < first_fps, (
+            f"单视频: setpts(position={last_setpts}) 应该在 fps(position={first_fps}) 之前。"
+            f"滤镜链: {chain_str}"
+        )
+
     def test_empty_layers_raises(self):
         """空图层列表抛出 ValueError。"""
         svc = _make_service()