diff --git a/apps/worker/video_processing/unified_render_service.py b/apps/worker/video_processing/unified_render_service.py
index 8e9d780b8..fbba0890f 100755
--- a/apps/worker/video_processing/unified_render_service.py
+++ b/apps/worker/video_processing/unified_render_service.py
@@ -1050,8 +1050,10 @@ class UnifiedRenderService:
 
         vf_str = ",".join(filters)
 
-        # 最终输出时长：取 clip 有效时长和 video_duration 的较小值
-        final_duration = effective_duration
+        # 最终输出时长：取 clip 调速后有效时长和 video_duration 的较小值
+        # 注意：必须用调速后的时长，否则减速场景（speed<1）会被 -t 截断
+        adjusted_duration = UnifiedRenderService._clip_adjusted_duration(clip)
+        final_duration = adjusted_duration
         if video_duration > 0 and (final_duration <= 0 or final_duration > video_duration):
             final_duration = video_duration
 
diff --git a/tests/unit/test_unified_render_service.py b/tests/unit/test_unified_render_service.py
index 837ff2d0f..f2bba9f49 100755
--- a/tests/unit/test_unified_render_service.py
+++ b/tests/unit/test_unified_render_service.py
@@ -47,6 +47,7 @@ class FakeClip:
     transition_effect: str = "cut"
     transition_duration: float = 0.0
     status: str = "ready"
+    playback_speed: float = 1.0
     config: dict[str, Any] = field(default_factory=dict)
 
 
@@ -68,6 +69,7 @@ def _make_clip(
     transition_effect: str = "cut",
     transition_duration: float = 0.0,
     config: dict[str, Any] | None = None,
+    playback_speed: float = 1.0,
 ) -> FakeClip:
     return FakeClip(
         id=clip_id,
@@ -78,6 +80,7 @@ def _make_clip(
         transition_effect=transition_effect,
         transition_duration=transition_duration,
         config=config or {},
+        playback_speed=playback_speed,
     )
 
 
@@ -1925,6 +1928,88 @@ class TestConcatNormalizeVideoResolution:
         vf_value = cmd[vf_idx + 1]
         assert "crop=" in vf_value, "background 层应有 crop 滤镜"
 
+    def test_pass_through_speed_up_correct_duration(self):
+        """直通模式加速（speed=2x）：视频+音频均调速，-t 时长为原始的 1/2。"""
+        clips = [_make_clip("c1", "main", order=0, duration=10.0, playback_speed=2.0)]
+        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=10.0),
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            resolved = svc._resolve_clips()
+            layers = svc._group_clips_into_layers(resolved)
+            svc._render_pass_through(layers, Path("/tmp/out.mp4"))
+
+        assert mock_run.called
+        cmd = mock_run.call_args[0][0]
+        cmd_str = " ".join(cmd)
+
+        # 视频调速：setpts=PTS/2.0
+        assert "setpts=PTS/2.0" in cmd_str, "加速场景应有 setpts=PTS/speed 滤镜"
+
+        # 音频调速：atempo
+        assert "atempo" in cmd_str, "加速场景应有 atempo 音频调速滤镜"
+
+        # 输出时长应为原始 / speed = 10 / 2 = 5 秒
+        t_idx = cmd.index("-t")
+        t_value = float(cmd[t_idx + 1])
+        assert abs(t_value - 5.0) < 0.01, f"加速后 -t 时长应为 5.0s，实际 {t_value}s"
+
+    def test_pass_through_slow_down_correct_duration(self):
+        """直通模式减速（speed=0.5x）：视频+音频均调速，-t 时长为原始的 2 倍（不被截断）。"""
+        clips = [_make_clip("c1", "main", order=0, duration=10.0, playback_speed=0.5)]
+        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=10.0),
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            resolved = svc._resolve_clips()
+            layers = svc._group_clips_into_layers(resolved)
+            svc._render_pass_through(layers, Path("/tmp/out.mp4"))
+
+        assert mock_run.called
+        cmd = mock_run.call_args[0][0]
+        cmd_str = " ".join(cmd)
+
+        # 视频调速：setpts=PTS/0.5
+        assert "setpts=PTS/0.5" in cmd_str, "减速场景应有 setpts=PTS/speed 滤镜"
+
+        # 音频调速：atempo
+        assert "atempo" in cmd_str, "减速场景应有 atempo 音频调速滤镜"
+
+        # 输出时长应为原始 / speed = 10 / 0.5 = 20 秒（减速后视频变长，不应被截断）
+        t_idx = cmd.index("-t")
+        t_value = float(cmd[t_idx + 1])
+        assert abs(t_value - 20.0) < 0.01, f"减速后 -t 时长应为 20.0s，实际 {t_value}s"
+
+    def test_pass_through_speed_with_video_duration_cap(self):
+        """直通模式调速 + video_duration 截断：取调速后时长与 video_duration 的较小值。"""
+        clips = [_make_clip("c1", "main", order=0, duration=10.0, playback_speed=2.0)]
+        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=10.0),
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            resolved = svc._resolve_clips()
+            layers = svc._group_clips_into_layers(resolved)
+            # video_duration=3.0 < 调速后时长 5.0，应取 3.0
+            svc._render_pass_through(layers, Path("/tmp/out.mp4"), video_duration=3.0)
+
+        assert mock_run.called
+        cmd = mock_run.call_args[0][0]
+        t_idx = cmd.index("-t")
+        t_value = float(cmd[t_idx + 1])
+        assert abs(t_value - 3.0) < 0.01, f"video_duration 更小时应取 video_duration，实际 {t_value}s"
+
 
 class TestConcatNormalizeVideoFps:
     """视频帧率归一化：fps 滤镜统一到目标 fps。