diff --git a/tests/unit/domain/test_video_filter_builder.py b/tests/unit/domain/test_video_filter_builder.py
new file mode 100755
index 000000000..f47d83e7b
--- /dev/null
+++ b/tests/unit/domain/test_video_filter_builder.py
@@ -0,0 +1,714 @@
+"""video_filter_builder 单测.
+
+domain 层纯逻辑模块，0 FFmpeg 依赖，快速轻量。
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+import pytest
+
+from packages.domain.video_filter_builder import (
+    DEFAULT_CLIP_DURATION,
+    DEFAULT_FPS,
+    DEFAULT_OUTPUT_HEIGHT,
+    DEFAULT_OUTPUT_WIDTH,
+    DEFAULT_TRANSITION_DURATION,
+    XFADE_TRANSITION_MAP,
+    ClipFilterChain,
+    build_clip_filter,
+    build_concat_filter,
+    build_filter_complex,
+    build_xfade_filter,
+    chain_filters,
+    has_audio,
+)
+
+# ── 工具函数 ──────────────────────────────────────────────────────────────────
+
+
+def _make_chain(
+    clip_id: str = "c1",
+    input_index: int = 0,
+    duration: float = 3.0,
+    has_audio: bool = True,
+    filters: list[str] | None = None,
+) -> ClipFilterChain:
+    """快速创建 ClipFilterChain."""
+    if filters is None:
+        filters = ["scale=1280:720", "fps=25", "trim=0:3"]
+    return ClipFilterChain(
+        clip_id=clip_id,
+        input_index=input_index,
+        video_label=f"v{input_index}",
+        audio_label=f"a{input_index}" if has_audio else None,
+        filters=filters,
+        duration=duration,
+    )
+
+
+def _mock_clip(
+    clip_id: str = "c1",
+    duration: float = 5.0,
+    start_time: float = 0.0,
+    clip_type: str = "video",
+) -> MagicMock:
+    """创建 mock 的 EditPlanClip."""
+    clip = MagicMock()
+    clip.id = clip_id
+    clip.duration = duration
+    clip.start_time = start_time
+    clip.clip_type = clip_type
+    return clip
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# 常量测试
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestConstants:
+    """常量默认值测试."""
+
+    def test_default_resolution(self):
+        """默认分辨率为 1280x720."""
+        assert DEFAULT_OUTPUT_WIDTH == 1280
+        assert DEFAULT_OUTPUT_HEIGHT == 720
+
+    def test_default_fps(self):
+        """默认帧率 25."""
+        assert DEFAULT_FPS == 25
+
+    def test_default_transition_duration(self):
+        """默认转场时长 0.5s."""
+        assert DEFAULT_TRANSITION_DURATION == 0.5
+
+    def test_default_clip_duration(self):
+        """默认片段时长 5s."""
+        assert DEFAULT_CLIP_DURATION == 5.0
+
+    def test_xfade_map_contains_common_transitions(self):
+        """xfade 转场映射包含常见类型."""
+        assert "fade" in XFADE_TRANSITION_MAP.values()
+        assert "slideleft" in XFADE_TRANSITION_MAP.values()
+        assert "slideright" in XFADE_TRANSITION_MAP.values()
+        assert "dissolve" in XFADE_TRANSITION_MAP.values()
+        assert "wipeleft" in XFADE_TRANSITION_MAP.values()
+        assert len(XFADE_TRANSITION_MAP) >= 5
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# ClipFilterChain 数据类
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestClipFilterChain:
+    """数据类结构测试."""
+
+    def test_creation(self):
+        """创建 ClipFilterChain."""
+        chain = ClipFilterChain(
+            clip_id="c1",
+            input_index=0,
+            video_label="v0",
+            audio_label="a0",
+            filters=["scale=1280:720"],
+            duration=5.0,
+        )
+        assert chain.clip_id == "c1"
+        assert chain.input_index == 0
+        assert chain.video_label == "v0"
+        assert chain.audio_label == "a0"
+        assert chain.filters == ["scale=1280:720"]
+        assert chain.duration == 5.0
+
+    def test_no_audio(self):
+        """无音频流."""
+        chain = _make_chain(has_audio=False)
+        assert chain.audio_label is None
+
+    def test_frozen(self):
+        """frozen dataclass 不可修改."""
+        chain = _make_chain()
+        with pytest.raises(Exception):
+            chain.duration = 10.0  # type: ignore
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# chain_filters
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestChainFilters:
+    """滤镜串联测试."""
+
+    def test_single_filter(self):
+        """单个滤镜."""
+        result = chain_filters(["scale=1280:720"], "v0")
+        assert result == "[0:v]scale=1280:720[v0]"
+
+    def test_multiple_filters(self):
+        """多个滤镜用逗号连接."""
+        result = chain_filters(["scale=1280:720", "fps=25", "trim=0:5"], "v0")
+        assert "scale=1280:720,fps=25,trim=0:5" in result
+        assert result.startswith("[0:v]")
+        assert result.endswith("[v0]")
+
+    def test_empty_filters(self):
+        """空滤镜列表."""
+        result = chain_filters([], "out")
+        assert result == "[0:v][out]"
+
+    def test_custom_input_label(self):
+        """自定义输入标签."""
+        result = chain_filters(["fps=30"], "v1", input_label="1:v")
+        assert result.startswith("[1:v]")
+        assert result.endswith("[v1]")
+
+    def test_custom_output_label(self):
+        """自定义输出标签."""
+        result = chain_filters(["scale=640:480"], "my_label")
+        assert result.endswith("[my_label]")
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# has_audio
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestHasAudio:
+    """音频判断测试."""
+
+    def test_all_have_audio(self):
+        """全部有音频."""
+        chains = [_make_chain(has_audio=True), _make_chain(has_audio=True)]
+        assert has_audio(chains) is True
+
+    def test_none_have_audio(self):
+        """全部无音频."""
+        chains = [_make_chain(has_audio=False), _make_chain(has_audio=False)]
+        assert has_audio(chains) is False
+
+    def test_partial_audio(self):
+        """部分有音频."""
+        chains = [_make_chain(has_audio=True), _make_chain(has_audio=False)]
+        assert has_audio(chains) is True
+
+    def test_empty_list(self):
+        """空列表."""
+        assert has_audio([]) is False
+
+    def test_single_with_audio(self):
+        """单个有音频."""
+        assert has_audio([_make_chain(has_audio=True)]) is True
+
+    def test_single_without_audio(self):
+        """单个无音频."""
+        assert has_audio([_make_chain(has_audio=False)]) is False
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# build_clip_filter
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestBuildClipFilter:
+    """单片段滤镜链构建测试."""
+
+    def test_basic_video_clip(self):
+        """基础视频片段."""
+        clip = _mock_clip(duration=5.0, start_time=0.0)
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert chain.clip_id == "c1"
+        assert chain.input_index == 0
+        assert chain.video_label == "v0"
+        assert chain.audio_label == "a0"
+        assert chain.duration == 5.0
+        assert len(chain.filters) >= 5
+
+    def test_contains_scale_filter(self):
+        """包含 scale 滤镜."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert any("scale=1280:720" in f for f in chain.filters)
+
+    def test_contains_pad_filter(self):
+        """包含 pad 滤镜（居中黑边）."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert any("pad=1280:720" in f for f in chain.filters)
+
+    def test_contains_format_filter(self):
+        """包含 format 滤镜（yuv420p）."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert any("format=yuv420p" in f for f in chain.filters)
+
+    def test_contains_fps_filter(self):
+        """包含 fps 滤镜."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 0, 1280, 720, 30)
+        assert any("fps=30" in f for f in chain.filters)
+
+    def test_zero_fps_skipped(self):
+        """fps=0 时跳过 fps 滤镜."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 0, 1280, 720, 0)
+        assert not any(f.startswith("fps=") for f in chain.filters)
+
+    def test_negative_fps_skipped(self):
+        """负 fps 跳过."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 0, 1280, 720, -1)
+        assert not any(f.startswith("fps=") for f in chain.filters)
+
+    def test_start_time_offset(self):
+        """有 start_time 时 setpts 带偏移."""
+        clip = _mock_clip(start_time=2.0)
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert any("PTS-STARTPTS+2.0/TB" in f for f in chain.filters)
+
+    def test_zero_start_time_no_offset(self):
+        """start_time=0 时无偏移."""
+        clip = _mock_clip(start_time=0.0)
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert any("setpts=PTS-STARTPTS" in f for f in chain.filters)
+        # 不含 +N/TB 偏移
+        setpts_filters = [f for f in chain.filters if f.startswith("setpts=")]
+        # 第一个 setpts 是重置的（不含偏移），trim 后还有一个
+        assert len(setpts_filters) >= 1
+
+    def test_contains_trim_filter(self):
+        """包含 trim 滤镜."""
+        clip = _mock_clip(duration=5.0)
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert any("trim=0:5.0" in f for f in chain.filters)
+
+    def test_negative_duration_uses_default(self):
+        """duration<=0 时使用默认时长."""
+        clip = _mock_clip(duration=0.0)
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert chain.duration == DEFAULT_CLIP_DURATION
+        assert any(f"trim=0:{DEFAULT_CLIP_DURATION}" in f for f in chain.filters)
+
+    def test_title_clip_no_audio(self):
+        """title 类型片段无音频."""
+        clip = _mock_clip(clip_type="title")
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert chain.audio_label is None
+
+    def test_subtitle_clip_no_audio(self):
+        """subtitle 类型片段无音频."""
+        clip = _mock_clip(clip_type="subtitle")
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert chain.audio_label is None
+
+    def test_video_clip_has_audio(self):
+        """video 类型片段有音频."""
+        clip = _mock_clip(clip_type="video")
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        assert chain.audio_label == "a0"
+
+    def test_image_clip_has_audio(self):
+        """image 类型默认有音频标签（实际无音流由调用方判断）."""
+        clip = _mock_clip(clip_type="image")
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        # 只有 title/subtitle 被排除
+        assert chain.audio_label is not None
+
+    def test_input_index_matches_label(self):
+        """input_index 对应标签编号."""
+        clip = _mock_clip()
+        chain = build_clip_filter(clip, 3, 1280, 720, 25)
+        assert chain.input_index == 3
+        assert chain.video_label == "v3"
+        assert chain.audio_label == "a3"
+
+    def test_filter_order(self):
+        """滤镜顺序：scale → pad → format → fps → setpts → trim."""
+        clip = _mock_clip(duration=5.0, start_time=1.0)
+        chain = build_clip_filter(clip, 0, 1280, 720, 25)
+        filter_names = [f.split("=")[0] for f in chain.filters]
+        # scale 在 pad 前
+        assert filter_names.index("scale") < filter_names.index("pad")
+        # pad 在 format 前
+        assert filter_names.index("pad") < filter_names.index("format")
+        # format 在 fps 前
+        assert filter_names.index("format") < filter_names.index("fps")
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# build_concat_filter
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestBuildConcatFilter:
+    """concat 滤镜构建测试."""
+
+    def test_empty_returns_empty(self):
+        """空列表返回空."""
+        result, duration = build_concat_filter([])
+        assert result == ""
+        assert duration == 0.0
+
+    def test_single_clip(self):
+        """单个片段."""
+        chain = _make_chain(clip_id="c1", input_index=0, duration=3.0)
+        result, total = build_concat_filter([chain])
+        assert "[0:v]" in result
+        assert "concat=n=1:v=1:a=0" in result
+        assert "[outv]" in result
+        assert total == 3.0
+
+    def test_two_clips(self):
+        """两个片段 concat."""
+        chains = [
+            _make_chain(clip_id="c1", input_index=0, duration=3.0),
+            _make_chain(clip_id="c2", input_index=1, duration=2.0),
+        ]
+        result, total = build_concat_filter(chains)
+        assert "[0:v]" in result
+        assert "[1:v]" in result
+        assert "concat=n=2:v=1:a=0[outv]" in result
+        assert total == 5.0
+
+    def test_three_clips(self):
+        """三个片段."""
+        chains = [
+            _make_chain(clip_id="c1", input_index=0, duration=2.0),
+            _make_chain(clip_id="c2", input_index=1, duration=3.0),
+            _make_chain(clip_id="c3", input_index=2, duration=1.0),
+        ]
+        result, total = build_concat_filter(chains)
+        assert "concat=n=3:v=1:a=0[outv]" in result
+        assert total == 6.0
+
+    def test_total_duration_sum(self):
+        """总时长 = 各片段时长之和."""
+        chains = [
+            _make_chain(duration=1.5),
+            _make_chain(duration=2.5),
+            _make_chain(duration=3.0),
+        ]
+        _, total = build_concat_filter(chains)
+        assert abs(total - 7.0) < 0.001
+
+    def test_audio_concat_with_audio(self):
+        """有音频时包含音频 concat."""
+        chains = [
+            _make_chain(input_index=0, has_audio=True),
+            _make_chain(input_index=1, has_audio=True),
+        ]
+        result, _ = build_concat_filter(chains)
+        assert "[outa]" in result
+        assert "concat=n=2:v=0:a=1[outa]" in result
+
+    def test_audio_normalization(self):
+        """音频经过 aformat 归一化."""
+        chains = [_make_chain(input_index=0, has_audio=True)]
+        result, _ = build_concat_filter(chains)
+        assert "aformat=sample_rates=48000" in result
+        assert "channel_layouts=stereo" in result
+        assert "sample_fmts=fltp" in result
+
+    def test_no_audio_concat(self):
+        """无音频时不生成音频 concat."""
+        chains = [
+            _make_chain(input_index=0, has_audio=False),
+            _make_chain(input_index=1, has_audio=False),
+        ]
+        result, _ = build_concat_filter(chains)
+        assert "[outa]" not in result
+        assert "aformat" not in result
+
+    def test_partial_audio_only_includes_audio_chains(self):
+        """部分有音频时，只对有音频的片段做 concat."""
+        chains = [
+            _make_chain(input_index=0, has_audio=True),
+            _make_chain(input_index=1, has_audio=False),
+            _make_chain(input_index=2, has_audio=True),
+        ]
+        result, _ = build_concat_filter(chains)
+        # 音频 concat 只有 2 个输入
+        assert "concat=n=2:v=0:a=1[outa]" in result
+
+    def test_video_labels_correct(self):
+        """视频标签正确."""
+        chains = [
+            _make_chain(clip_id="a", input_index=0, duration=1.0),
+            _make_chain(clip_id="b", input_index=1, duration=1.0),
+        ]
+        result, _ = build_concat_filter(chains)
+        assert "[v0]" in result
+        assert "[v1]" in result
+
+    def test_filter_chain_applied_per_clip(self):
+        """每个片段都有独立的滤镜链."""
+        chains = [
+            _make_chain(input_index=0, filters=["scale=1280:720", "fps=25"]),
+            _make_chain(input_index=1, filters=["scale=1280:720", "fps=25"]),
+        ]
+        result, _ = build_concat_filter(chains)
+        # 两个片段都有滤镜处理
+        assert result.count("scale=1280:720") == 2
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# build_xfade_filter
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestBuildXfadeFilter:
+    """xfade 转场滤镜构建测试."""
+
+    def test_empty_returns_empty(self):
+        """空列表返回空."""
+        result, duration = build_xfade_filter([], 0.5, [])
+        assert result == ""
+        assert duration == 0.0
+
+    def test_single_clip_copy(self):
+        """单个片段用 copy 直接输出."""
+        chain = _make_chain(clip_id="c1", input_index=0, duration=3.0)
+        result, total = build_xfade_filter([chain], 0.5, [])
+        assert "copy[outv]" in result
+        assert total == 3.0
+
+    def test_two_clips_fade_transition(self):
+        """两个片段 + fade 转场."""
+        chains = [
+            _make_chain(input_index=0, duration=3.0),
+            _make_chain(input_index=1, duration=2.0),
+        ]
+        result, total = build_xfade_filter(chains, 0.5, ["cut", "fade"])
+        assert "xfade=transition=fade" in result
+        assert "duration=0.5" in result
+        assert "[outv]" in result
+        # 总时长 = 3 + 2 - 0.5 = 4.5
+        assert abs(total - 4.5) < 0.001
+
+    def test_three_clips_with_transitions(self):
+        """三个片段 + 多个转场."""
+        chains = [
+            _make_chain(input_index=0, duration=3.0),
+            _make_chain(input_index=1, duration=2.0),
+            _make_chain(input_index=2, duration=4.0),
+        ]
+        result, total = build_xfade_filter(chains, 0.5, ["cut", "fade", "slideleft"])
+        # 两个 xfade 转场
+        assert result.count("xfade=") == 2
+        assert "xf1" in result  # 中间标签
+        # 总时长 = 3+2+4 - 0.5*2 = 8.0
+        assert abs(total - 8.0) < 0.001
+
+    def test_offset_calculation(self):
+        """转场 offset 计算正确."""
+        chains = [
+            _make_chain(input_index=0, duration=5.0),
+            _make_chain(input_index=1, duration=3.0),
+        ]
+        result, _ = build_xfade_filter(chains, 1.0, ["cut", "fade"])
+        # offset = 5.0 - 1.0*1 = 4.0
+        assert "offset=4.000" in result
+
+    def test_offset_never_negative(self):
+        """offset 不为负."""
+        chains = [
+            _make_chain(input_index=0, duration=0.3),
+            _make_chain(input_index=1, duration=0.3),
+        ]
+        result, _ = build_xfade_filter(chains, 1.0, ["cut", "fade"])
+        # offset = max(0, 0.3 - 1.0) = 0
+        assert "offset=0.000" in result
+
+    def test_transition_slide_left(self):
+        """slideleft 转场."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=2.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "slide_left"])
+        assert "xfade=transition=slideleft" in result
+
+    def test_transition_slide_right(self):
+        """slideright 转场."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=2.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "slide_right"])
+        assert "xfade=transition=slideright" in result
+
+    def test_transition_dissolve(self):
+        """dissolve 转场."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=2.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "dissolve"])
+        assert "xfade=transition=dissolve" in result
+
+    def test_unknown_transition_defaults_to_fade(self):
+        """未知转场默认 fade."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=2.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "unknown_transition"])
+        assert "xfade=transition=fade" in result
+
+    def test_total_duration_minus_overlap(self):
+        """总时长 = sum - transition_duration * (n-1)."""
+        chains = [
+            _make_chain(duration=10.0),
+            _make_chain(duration=10.0),
+            _make_chain(duration=10.0),
+        ]
+        _, total = build_xfade_filter(chains, 1.0, ["cut", "fade", "wipe"])
+        # 30 - 2 = 28
+        assert abs(total - 28.0) < 0.001
+
+    def test_total_duration_never_negative(self):
+        """总时长不为负."""
+        chains = [
+            _make_chain(duration=0.1),
+            _make_chain(duration=0.1),
+        ]
+        _, total = build_xfade_filter(chains, 10.0, ["cut", "fade"])
+        assert total >= 0.0
+
+    def test_audio_with_xfade_path(self):
+        """xfade 路径下音频也做 concat."""
+        chains = [
+            _make_chain(input_index=0, has_audio=True, duration=2.0),
+            _make_chain(input_index=1, has_audio=True, duration=3.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "fade"])
+        assert "[outa]" in result
+        assert "aformat=" in result
+
+    def test_single_xfade_no_audio_processing(self):
+        """单片段 xfade 路径不处理音频（与原实现一致）."""
+        chain = _make_chain(input_index=0, has_audio=True, duration=3.0)
+        result, _ = build_xfade_filter([chain], 0.5, [])
+        # 单片段 xfade 只有视频 copy，不处理音频
+        assert "copy[outv]" in result
+        assert "[outa]" not in result
+        assert "acopy" not in result
+
+    def test_no_audio_xfade(self):
+        """无音频时不生成 [outa]."""
+        chains = [
+            _make_chain(input_index=0, has_audio=False, duration=2.0),
+            _make_chain(input_index=1, has_audio=False, duration=2.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "fade"])
+        assert "[outa]" not in result
+
+    def test_intermediate_labels(self):
+        """多片段时有中间 xf 标签."""
+        chains = [
+            _make_chain(input_index=0, duration=1.0),
+            _make_chain(input_index=1, duration=1.0),
+            _make_chain(input_index=2, duration=1.0),
+            _make_chain(input_index=3, duration=1.0),
+        ]
+        result, _ = build_xfade_filter(chains, 0.3, ["cut", "fade", "wipe", "dissolve"])
+        assert "[xf1]" in result
+        assert "[xf2]" in result
+        assert "[outv]" in result
+
+    def test_transitions_shorter_than_clips(self):
+        """transitions 列表比片段短时，后续用默认值."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=2.0),
+            _make_chain(input_index=2, duration=2.0),
+        ]
+        # 只给一个转场（索引1有效，索引2越界）
+        result, _ = build_xfade_filter(chains, 0.5, ["cut", "fade"])
+        # 第2个转场（索引2）未知 → 默认 fade
+        assert result.count("xfade=transition=fade") == 2
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# build_filter_complex
+# ═══════════════════════════════════════════════════════════════════════════════
+
+
+class TestBuildFilterComplex:
+    """完整 filter_complex 构建（策略选择）测试."""
+
+    def test_empty_returns_empty(self):
+        """空列表返回空."""
+        result, duration = build_filter_complex([], 1280, 720, 0.5, [])
+        assert result == ""
+        assert duration == 0.0
+
+    def test_single_clip_chain_mode(self):
+        """单片段走单链模式."""
+        chain = _make_chain(input_index=0, duration=3.0, has_audio=True)
+        result, total = build_filter_complex([chain], 1280, 720, 0.5, [])
+        assert "[0:v]" in result
+        assert "[0:a]" in result
+        assert total == 3.0
+
+    def test_single_clip_no_audio(self):
+        """单片段无音频."""
+        chain = _make_chain(input_index=0, duration=3.0, has_audio=False)
+        result, _ = build_filter_complex([chain], 1280, 720, 0.5, [])
+        assert "[0:a]" not in result
+
+    def test_multiple_clips_all_cut_uses_concat(self):
+        """多片段 + 全 cut → 走 concat（高效模式）."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=3.0),
+        ]
+        result, total = build_filter_complex(chains, 1280, 720, 0.5, ["cut", "cut"])
+        # concat 模式
+        assert "concat=n=2:v=1:a=0" in result
+        assert "xfade" not in result
+        assert total == 5.0
+
+    def test_multiple_clips_with_transition_uses_xfade(self):
+        """多片段 + 有转场 → 走 xfade."""
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=3.0),
+        ]
+        result, total = build_filter_complex(chains, 1280, 720, 0.5, ["cut", "fade"])
+        assert "xfade=" in result
+        assert abs(total - 4.5) < 0.001
+
+    def test_transition_effect_enum_value(self):
+        """使用 TransitionEffect 枚举值也能正确判断."""
+        from packages.domain.template_clip_config import TransitionEffect
+
+        chains = [
+            _make_chain(input_index=0, duration=2.0),
+            _make_chain(input_index=1, duration=2.0),
+        ]
+        # 传 TransitionEffect.CUT（不是字符串 "cut"）
+        result, _ = build_filter_complex(
+            chains,
+            1280,
+            720,
+            0.5,
+            [TransitionEffect.CUT, TransitionEffect.CUT],
+        )
+        # 都是 cut → 走 concat
+        assert "concat=n=2:v=1:a=0" in result
+
+    def test_mixed_cut_and_transition(self):
+        """混合 cut 和转场 → 走 xfade."""
+        chains = [
+            _make_chain(input_index=0, duration=1.0),
+            _make_chain(input_index=1, duration=1.0),
+            _make_chain(input_index=2, duration=1.0),
+        ]
+        result, total = build_filter_complex(chains, 1280, 720, 0.5, ["cut", "fade", "cut"])
+        # 只要有一个非 cut 转场就走 xfade
+        assert "xfade=" in result
+        assert abs(total - 2.0) < 0.001