diff --git a/tests/unit/test_concat_engine.py b/tests/unit/test_concat_engine.py
new file mode 100755
index 000000000..6aff69220
--- /dev/null
+++ b/tests/unit/test_concat_engine.py
@@ -0,0 +1,234 @@
+"""
+视频拼接引擎配置与纯逻辑测试.
+
+覆盖 ConcatSegment.from_dict / ConcatConfig.from_config_dict / has_effect / total_segments 等纯逻辑.
+引擎核心 render 方法依赖 FFmpeg，由集成测试覆盖.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from video_processing.concat_engine import ConcatConfig, ConcatSegment
+
+
+class TestConcatSegmentFromDict:
+    """ConcatSegment.from_dict 构造逻辑."""
+
+    def test_basic(self):
+        seg = ConcatSegment.from_dict({"video_path": "/tmp/a.mp4"})
+        assert seg.video_path == "/tmp/a.mp4"
+        assert seg.start_time == 0.0
+        assert seg.duration == 0.0
+        assert seg.has_audio is True
+
+    def test_full_fields(self):
+        seg = ConcatSegment.from_dict({
+            "video_path": "/tmp/b.mp4",
+            "start_time": 5.5,
+            "duration": 10.0,
+            "has_audio": False,
+        })
+        assert seg.video_path == "/tmp/b.mp4"
+        assert seg.start_time == 5.5
+        assert seg.duration == 10.0
+        assert seg.has_audio is False
+
+    def test_negative_start_time_clamped(self):
+        seg = ConcatSegment.from_dict({
+            "video_path": "/tmp/a.mp4",
+            "start_time": -1.0,
+        })
+        assert seg.start_time == 0.0
+
+    def test_negative_duration_clamped(self):
+        seg = ConcatSegment.from_dict({
+            "video_path": "/tmp/a.mp4",
+            "duration": -5.0,
+        })
+        assert seg.duration == 0.0
+
+    def test_invalid_start_time_type_falls_back(self):
+        seg = ConcatSegment.from_dict({
+            "video_path": "/tmp/a.mp4",
+            "start_time": "not_a_number",
+        })
+        assert seg.start_time == 0.0
+
+    def test_invalid_duration_type_falls_back(self):
+        seg = ConcatSegment.from_dict({
+            "video_path": "/tmp/a.mp4",
+            "duration": "abc",
+        })
+        assert seg.duration == 0.0
+
+    def test_start_time_none_falls_back(self):
+        seg = ConcatSegment.from_dict({
+            "video_path": "/tmp/a.mp4",
+            "start_time": None,
+        })
+        assert seg.start_time == 0.0
+
+    def test_empty_video_path_stored(self):
+        seg = ConcatSegment.from_dict({"video_path": ""})
+        assert seg.video_path == ""
+
+
+class TestConcatConfigFromConfigDict:
+    """ConcatConfig.from_config_dict 构造逻辑."""
+
+    def test_none_returns_default(self):
+        cfg = ConcatConfig.from_config_dict(None)
+        assert cfg.segments == []
+        assert cfg.output_width == 0
+        assert cfg.output_height == 0
+        assert cfg.output_fps == 0.0
+        assert cfg.force_reencode is False
+
+    def test_empty_dict_returns_default(self):
+        cfg = ConcatConfig.from_config_dict({})
+        assert cfg.segments == []
+
+    def test_non_dict_returns_default(self):
+        cfg = ConcatConfig.from_config_dict("not a dict")
+        assert cfg.segments == []
+
+    def test_single_segment(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [
+                {"video_path": "/tmp/a.mp4", "duration": 5.0},
+            ],
+        })
+        assert len(cfg.segments) == 1
+        assert cfg.segments[0].video_path == "/tmp/a.mp4"
+        assert cfg.segments[0].duration == 5.0
+
+    def test_multiple_segments(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [
+                {"video_path": "/tmp/a.mp4"},
+                {"video_path": "/tmp/b.mp4", "start_time": 2.0},
+                {"video_path": "/tmp/c.mp4", "duration": 3.0, "has_audio": False},
+            ],
+        })
+        assert len(cfg.segments) == 3
+        assert cfg.segments[0].video_path == "/tmp/a.mp4"
+        assert cfg.segments[1].start_time == 2.0
+        assert cfg.segments[2].has_audio is False
+
+    def test_invalid_segments_filtered(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [
+                {"video_path": "/tmp/valid.mp4"},
+                {"video_path": ""},  # 空路径被过滤
+                {"not_video_path": "xxx"},  # 没有video_path被过滤
+                "not_a_dict",  # 不是dict被过滤
+                None,  # None被过滤
+            ],
+        })
+        assert len(cfg.segments) == 1
+        assert cfg.segments[0].video_path == "/tmp/valid.mp4"
+
+    def test_segments_not_a_list(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": "not_a_list",
+        })
+        assert cfg.segments == []
+
+    def test_output_params(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [],
+            "output_width": 1920,
+            "output_height": 1080,
+            "output_fps": 30.0,
+            "force_reencode": True,
+        })
+        assert cfg.output_width == 1920
+        assert cfg.output_height == 1080
+        assert cfg.output_fps == 30.0
+        assert cfg.force_reencode is True
+
+    def test_negative_output_params_clamped(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [],
+            "output_width": -100,
+            "output_height": -50,
+            "output_fps": -1.0,
+        })
+        assert cfg.output_width == 0
+        assert cfg.output_height == 0
+        assert cfg.output_fps == 0.0
+
+    def test_invalid_output_params_fall_back(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [],
+            "output_width": "abc",
+            "output_height": None,
+            "output_fps": "xyz",
+        })
+        assert cfg.output_width == 0
+        assert cfg.output_height == 0
+        assert cfg.output_fps == 0.0
+
+    def test_transition_config(self):
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [],
+            "transition": "crossfade",
+            "transition_duration": 1.0,
+        })
+        assert cfg.transition == "crossfade"
+        assert cfg.transition_duration == 1.0
+
+    def test_transition_duration_minimum(self):
+        """transition_duration 不能小于 0.1."""
+        cfg = ConcatConfig.from_config_dict({
+            "segments": [],
+            "transition_duration": 0.01,
+        })
+        assert cfg.transition_duration >= 0.1
+
+    def test_default_values(self):
+        cfg = ConcatConfig.from_config_dict({"segments": []})
+        assert cfg.transition == "none"
+        assert cfg.transition_duration == 0.3
+        assert cfg.force_reencode is False
+
+
+class TestConcatConfigProperties:
+    """has_effect / total_segments 属性."""
+
+    def test_has_effect_two_or_more_valid(self):
+        cfg = ConcatConfig(segments=[
+            ConcatSegment(video_path="/tmp/a.mp4"),
+            ConcatSegment(video_path="/tmp/b.mp4"),
+        ])
+        assert cfg.has_effect is True
+
+    def test_no_effect_one_segment(self):
+        cfg = ConcatConfig(segments=[
+            ConcatSegment(video_path="/tmp/a.mp4"),
+        ])
+        assert cfg.has_effect is False
+
+    def test_no_effect_zero_segments(self):
+        cfg = ConcatConfig(segments=[])
+        assert cfg.has_effect is False
+
+    def test_no_effect_empty_paths(self):
+        cfg = ConcatConfig(segments=[
+            ConcatSegment(video_path=""),
+            ConcatSegment(video_path=""),
+        ])
+        assert cfg.has_effect is False
+
+    def test_total_segments(self):
+        cfg = ConcatConfig(segments=[
+            ConcatSegment(video_path="/tmp/a.mp4"),
+            ConcatSegment(video_path=""),
+            ConcatSegment(video_path="/tmp/b.mp4"),
+        ])
+        assert cfg.total_segments == 2
+
+    def test_total_segments_empty(self):
+        cfg = ConcatConfig(segments=[])
+        assert cfg.total_segments == 0
diff --git a/tests/unit/test_intro_outro_engine.py b/tests/unit/test_intro_outro_engine.py
new file mode 100755
index 000000000..f9112eca4
--- /dev/null
+++ b/tests/unit/test_intro_outro_engine.py
@@ -0,0 +1,302 @@
+"""
+片头片尾引擎配置与纯逻辑测试.
+
+覆盖 IntroOutroConfig.from_dict / validate / has_intro / has_outro 等纯逻辑.
+引擎核心 render 方法依赖 FFmpeg，由集成测试覆盖.
+"""
+
+import pytest
+
+from video_processing.intro_outro_engine import IntroOutroConfig
+
+
+class TestIntroOutroConfigFromDict:
+    """from_dict 构造逻辑."""
+
+    def test_none_returns_default_disabled(self):
+        cfg = IntroOutroConfig.from_dict(None)
+        assert cfg.enabled is False
+        assert cfg.intro_type == "none"
+        assert cfg.outro_type == "none"
+
+    def test_empty_dict_returns_default_disabled(self):
+        cfg = IntroOutroConfig.from_dict({})
+        assert cfg.enabled is False
+
+    def test_enabled_false_returns_default_disabled(self):
+        cfg = IntroOutroConfig.from_dict({"enabled": False})
+        assert cfg.enabled is False
+
+    def test_enabled_with_video_intro(self):
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {
+                "type": "video",
+                "video_path": "/tmp/intro.mp4",
+                "duration": 5.0,
+            },
+            "outro": {"type": "none"},
+        })
+        assert cfg.enabled is True
+        assert cfg.intro_type == "video"
+        assert cfg.intro_video_path == "/tmp/intro.mp4"
+        assert cfg.intro_duration == 5.0
+
+    def test_enabled_with_text_intro(self):
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {
+                "type": "text",
+                "title": "Hello",
+                "subtitle": "World",
+                "background": "#ffffff",
+                "title_color": "black",
+                "title_size": 64,
+                "duration": 2.5,
+            },
+            "outro": {"type": "none"},
+        })
+        assert cfg.enabled is True
+        assert cfg.intro_type == "text"
+        assert cfg.intro_title == "Hello"
+        assert cfg.intro_subtitle == "World"
+        assert cfg.intro_background == "#ffffff"
+        assert cfg.intro_title_color == "black"
+        assert cfg.intro_title_size == 64
+        assert cfg.intro_duration == 2.5
+
+    def test_enabled_with_video_outro(self):
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {"type": "none"},
+            "outro": {
+                "type": "video",
+                "video_path": "/tmp/outro.mp4",
+                "duration": 4.0,
+            },
+        })
+        assert cfg.enabled is True
+        assert cfg.outro_type == "video"
+        assert cfg.outro_video_path == "/tmp/outro.mp4"
+        assert cfg.outro_duration == 4.0
+
+    def test_enabled_with_text_outro_default_values(self):
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {"type": "none"},
+            "outro": {"type": "text"},
+        })
+        assert cfg.outro_title == "感谢观看"
+        assert cfg.outro_subtitle == "点赞关注不迷路"
+        assert cfg.outro_title_size == 48
+        assert cfg.outro_duration == 3.0
+
+    def test_video_key_fallback(self):
+        """video 字段作为 video_path 的 fallback."""
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {
+                "type": "video",
+                "video": "/tmp/fallback.mp4",
+            },
+            "outro": {"type": "none"},
+        })
+        assert cfg.intro_video_path == "/tmp/fallback.mp4"
+
+    def test_transition_config(self):
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {"type": "none"},
+            "outro": {"type": "none"},
+            "transition": "fade",
+            "transition_duration": 1.0,
+        })
+        assert cfg.transition_effect == "fade"
+        assert cfg.transition_duration == 1.0
+
+    def test_default_transition(self):
+        cfg = IntroOutroConfig.from_dict({
+            "enabled": True,
+            "intro": {"type": "none"},
+            "outro": {"type": "none"},
+        })
+        assert cfg.transition_effect == "fade"
+        assert cfg.transition_duration == 0.5
+
+
+class TestIntroOutroConfigProperties:
+    """has_intro / has_outro 属性."""
+
+    def test_has_intro_video_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="video",
+            intro_video_path="/tmp/a.mp4",
+        )
+        assert cfg.has_intro is True
+
+    def test_has_intro_text_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="text",
+            intro_title="Hi",
+        )
+        assert cfg.has_intro is True
+
+    def test_no_intro_when_disabled(self):
+        cfg = IntroOutroConfig(
+            enabled=False,
+            intro_type="video",
+            intro_video_path="/tmp/a.mp4",
+        )
+        assert cfg.has_intro is False
+
+    def test_no_intro_when_none_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="none",
+        )
+        assert cfg.has_intro is False
+
+    def test_has_outro_video_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            outro_type="video",
+            outro_video_path="/tmp/a.mp4",
+        )
+        assert cfg.has_outro is True
+
+    def test_has_outro_text_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            outro_type="text",
+            outro_title="Bye",
+        )
+        assert cfg.has_outro is True
+
+    def test_has_outro_follow_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            outro_type="follow",
+            outro_title="Follow me",
+        )
+        assert cfg.has_outro is True
+
+    def test_no_outro_when_disabled(self):
+        cfg = IntroOutroConfig(
+            enabled=False,
+            outro_type="text",
+            outro_title="Bye",
+        )
+        assert cfg.has_outro is False
+
+    def test_no_outro_when_none_type(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            outro_type="none",
+        )
+        assert cfg.has_outro is False
+
+
+class TestIntroOutroConfigValidate:
+    """validate 校验逻辑."""
+
+    def test_disabled_is_valid(self):
+        cfg = IntroOutroConfig(enabled=False)
+        ok, msg = cfg.validate()
+        assert ok is True
+        assert msg == ""
+
+    def test_video_intro_missing_path(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="video",
+            intro_video_path="",
+            outro_type="none",
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "video_path" in msg
+
+    def test_text_intro_missing_title(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="text",
+            intro_title="",
+            outro_type="none",
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "title" in msg
+
+    def test_video_outro_missing_path(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="none",
+            outro_type="video",
+            outro_video_path="",
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "video_path" in msg
+
+    def test_text_outro_missing_title(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="none",
+            outro_type="text",
+            outro_title="",
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "title" in msg
+
+    def test_intro_duration_zero(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="text",
+            intro_title="Hi",
+            intro_duration=0,
+            outro_type="none",
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "片头时长" in msg
+
+    def test_intro_duration_negative(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="text",
+            intro_title="Hi",
+            intro_duration=-1.0,
+            outro_type="none",
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "片头时长" in msg
+
+    def test_outro_duration_zero(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="none",
+            outro_type="text",
+            outro_title="Bye",
+            outro_duration=0,
+        )
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "片尾时长" in msg
+
+    def test_valid_full_config(self):
+        cfg = IntroOutroConfig(
+            enabled=True,
+            intro_type="video",
+            intro_video_path="/tmp/intro.mp4",
+            intro_duration=3.0,
+            outro_type="text",
+            outro_title="Thanks",
+            outro_duration=2.0,
+        )
+        ok, msg = cfg.validate()
+        assert ok is True
+        assert msg == ""
diff --git a/tests/unit/test_multi_track_mixer.py b/tests/unit/test_multi_track_mixer.py
new file mode 100755
index 000000000..244141413
--- /dev/null
+++ b/tests/unit/test_multi_track_mixer.py
@@ -0,0 +1,346 @@
+"""
+多轨道混音引擎配置与纯逻辑测试.
+
+覆盖 AudioTrack.from_dict / MultiTrackMixConfig.from_config_dict / has_effect 等纯逻辑.
+引擎核心混音方法依赖 FFmpeg，由集成测试覆盖.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from video_processing.multi_track_mixer import (
+    DEFAULT_VOLUMES,
+    MAX_AUDIO_TRACKS,
+    TRACK_TYPE_AMBIENT,
+    TRACK_TYPE_BGM,
+    TRACK_TYPE_MAIN,
+    TRACK_TYPE_SFX,
+    TRACK_TYPE_VOICEOVER,
+    AudioTrack,
+    MultiTrackMixConfig,
+)
+
+
+class TestTrackConstants:
+    """轨道类型常量与默认值."""
+
+    def test_track_types_exist(self):
+        assert TRACK_TYPE_MAIN == "main"
+        assert TRACK_TYPE_BGM == "bgm"
+        assert TRACK_TYPE_VOICEOVER == "voiceover"
+        assert TRACK_TYPE_SFX == "sfx"
+        assert TRACK_TYPE_AMBIENT == "ambient"
+
+    def test_max_tracks(self):
+        assert MAX_AUDIO_TRACKS == 8
+
+    def test_default_volumes(self):
+        assert DEFAULT_VOLUMES[TRACK_TYPE_MAIN] == 1.0
+        assert DEFAULT_VOLUMES[TRACK_TYPE_BGM] == 0.3
+        assert DEFAULT_VOLUMES[TRACK_TYPE_VOICEOVER] == 1.0
+        assert DEFAULT_VOLUMES[TRACK_TYPE_SFX] == 0.7
+        assert DEFAULT_VOLUMES[TRACK_TYPE_AMBIENT] == 0.2
+
+
+class TestAudioTrackFromDict:
+    """AudioTrack.from_dict 构造逻辑."""
+
+    def test_basic(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+        })
+        assert track.track_id == "t1"
+        assert track.track_type == "bgm"
+        assert track.audio_path == "/tmp/bgm.mp3"
+        assert track.volume == 0.3  # bgm 默认音量
+
+    def test_custom_volume(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "main",
+            "audio_path": "/tmp/main.wav",
+            "volume": 0.8,
+        })
+        assert track.volume == 0.8
+
+    def test_volume_clamped_to_zero(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "sfx",
+            "audio_path": "/tmp/sfx.wav",
+            "volume": -1.0,
+        })
+        assert track.volume == 0.0
+
+    def test_volume_clamped_to_max(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "sfx",
+            "audio_path": "/tmp/sfx.wav",
+            "volume": 3.0,
+        })
+        assert track.volume == 2.0
+
+    def test_invalid_volume_falls_back_to_default(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "volume": "not_a_number",
+        })
+        assert track.volume == 0.3  # bgm 默认
+
+    def test_none_volume_falls_back(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "voiceover",
+            "audio_path": "/tmp/vo.wav",
+            "volume": None,
+        })
+        assert track.volume == 1.0  # voiceover 默认
+
+    def test_unknown_track_type_default_volume(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "unknown_type",
+            "audio_path": "/tmp/a.wav",
+        })
+        assert track.volume == 1.0  # 未知类型默认 1.0
+
+    def test_fade_in_fade_out(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "fade_in": 1.5,
+            "fade_out": 2.0,
+        })
+        assert track.fade_in == 1.5
+        assert track.fade_out == 2.0
+
+    def test_negative_fade_clamped(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "fade_in": -0.5,
+            "fade_out": -1.0,
+        })
+        assert track.fade_in == 0.0
+        assert track.fade_out == 0.0
+
+    def test_invalid_fade_falls_back(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "fade_in": "abc",
+            "fade_out": None,
+        })
+        assert track.fade_in == 0.0
+        assert track.fade_out == 0.0
+
+    def test_start_time_and_duration(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "sfx",
+            "audio_path": "/tmp/sfx.wav",
+            "start_time": 5.0,
+            "duration": 3.0,
+        })
+        assert track.start_time == 5.0
+        assert track.duration == 3.0
+
+    def test_negative_start_time_clamped(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "start_time": -10.0,
+            "duration": -2.0,
+        })
+        assert track.start_time == 0.0
+        assert track.duration == 0.0
+
+    def test_invalid_time_values_fall_back(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "start_time": "invalid",
+            "duration": "bad",
+        })
+        assert track.start_time == 0.0
+        assert track.duration == 0.0
+
+    def test_enabled_default_true(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+        })
+        assert track.enabled is True
+
+    def test_enabled_can_be_false(self):
+        track = AudioTrack.from_dict({
+            "track_id": "t1",
+            "track_type": "bgm",
+            "audio_path": "/tmp/bgm.mp3",
+            "enabled": False,
+        })
+        assert track.enabled is False
+
+
+class TestMultiTrackMixConfigFromDict:
+    """MultiTrackMixConfig.from_config_dict 构造逻辑."""
+
+    def test_none_returns_default(self):
+        cfg = MultiTrackMixConfig.from_config_dict(None)
+        assert cfg.tracks == []
+        assert cfg.master_volume == 1.0
+        assert cfg.normalize is True
+
+    def test_empty_dict_returns_default(self):
+        cfg = MultiTrackMixConfig.from_config_dict({})
+        assert cfg.tracks == []
+
+    def test_non_dict_returns_default(self):
+        cfg = MultiTrackMixConfig.from_config_dict([])
+        assert cfg.tracks == []
+
+    def test_single_track(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [
+                {
+                    "track_id": "bgm1",
+                    "track_type": "bgm",
+                    "audio_path": "/tmp/bgm.mp3",
+                    "volume": 0.5,
+                },
+            ],
+        })
+        assert len(cfg.tracks) == 1
+        assert cfg.tracks[0].track_id == "bgm1"
+        assert cfg.tracks[0].volume == 0.5
+
+    def test_multiple_tracks(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [
+                {"track_id": "m", "track_type": "main", "audio_path": "/tmp/m.wav"},
+                {"track_id": "b", "track_type": "bgm", "audio_path": "/tmp/b.mp3"},
+                {"track_id": "v", "track_type": "voiceover", "audio_path": "/tmp/v.wav"},
+            ],
+        })
+        assert len(cfg.tracks) == 3
+        assert cfg.tracks[0].track_type == "main"
+        assert cfg.tracks[1].track_type == "bgm"
+        assert cfg.tracks[2].track_type == "voiceover"
+
+    def test_disabled_tracks_filtered(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [
+                {"track_id": "a", "track_type": "sfx", "audio_path": "/tmp/a.wav"},
+                {"track_id": "b", "track_type": "sfx", "audio_path": "/tmp/b.wav", "enabled": False},
+                {"track_id": "c", "track_type": "sfx", "audio_path": "/tmp/c.wav"},
+            ],
+        })
+        assert len(cfg.tracks) == 2
+        assert all(t.track_id != "b" for t in cfg.tracks)
+
+    def test_empty_audio_path_filtered(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [
+                {"track_id": "valid", "track_type": "sfx", "audio_path": "/tmp/a.wav"},
+                {"track_id": "empty", "track_type": "sfx", "audio_path": ""},
+            ],
+        })
+        assert len(cfg.tracks) == 1
+        assert cfg.tracks[0].track_id == "valid"
+
+    def test_invalid_tracks_skipped(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [
+                {"track_id": "ok", "track_type": "sfx", "audio_path": "/tmp/a.wav"},
+                "not_a_dict",
+                None,
+                {"no_audio_path": "xxx"},
+            ],
+        })
+        assert len(cfg.tracks) == 1
+
+    def test_tracks_not_a_list(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": "not_a_list",
+        })
+        assert cfg.tracks == []
+
+    def test_master_volume(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [],
+            "master_volume": 0.8,
+        })
+        assert cfg.master_volume == 0.8
+
+    def test_master_volume_clamped(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [],
+            "master_volume": 3.0,
+        })
+        assert cfg.master_volume == 2.0
+
+        cfg2 = MultiTrackMixConfig.from_config_dict({
+            "tracks": [],
+            "master_volume": -1.0,
+        })
+        assert cfg2.master_volume == 0.0
+
+    def test_invalid_master_volume_falls_back(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [],
+            "master_volume": "abc",
+        })
+        assert cfg.master_volume == 1.0
+
+    def test_normalize_and_max_output(self):
+        cfg = MultiTrackMixConfig.from_config_dict({
+            "tracks": [],
+            "normalize": False,
+            "max_output_volume": 2.0,
+        })
+        assert cfg.normalize is False
+        assert cfg.max_output_volume == 2.0
+
+    def test_default_values(self):
+        cfg = MultiTrackMixConfig.from_config_dict({"tracks": []})
+        assert cfg.master_volume == 1.0
+        assert cfg.normalize is True
+        assert cfg.max_output_volume == 1.5
+
+
+class TestMultiTrackMixConfigProperties:
+    """has_effect 属性."""
+
+    def test_has_effect_with_tracks(self):
+        cfg = MultiTrackMixConfig(tracks=[
+            AudioTrack(track_id="t1", track_type="bgm", audio_path="/tmp/a.mp3"),
+        ])
+        assert cfg.has_effect is True
+
+    def test_no_effect_empty(self):
+        cfg = MultiTrackMixConfig(tracks=[])
+        assert cfg.has_effect is False
+
+    def test_no_effect_all_disabled(self):
+        cfg = MultiTrackMixConfig(tracks=[
+            AudioTrack(track_id="t1", track_type="bgm", audio_path="/tmp/a.mp3", enabled=False),
+        ])
+        assert cfg.has_effect is False
+
+    def test_no_effect_empty_paths(self):
+        cfg = MultiTrackMixConfig(tracks=[
+            AudioTrack(track_id="t1", track_type="bgm", audio_path=""),
+        ])
+        assert cfg.has_effect is False
diff --git a/tests/unit/test_watermark_engine.py b/tests/unit/test_watermark_engine.py
new file mode 100755
index 000000000..5a8711d0d
--- /dev/null
+++ b/tests/unit/test_watermark_engine.py
@@ -0,0 +1,258 @@
+"""
+水印引擎配置与纯逻辑测试.
+
+覆盖 WatermarkConfig.from_dict / validate / 位置枚举等纯逻辑.
+引擎核心 render 方法依赖 FFmpeg，由集成测试覆盖.
+"""
+
+import pytest
+
+from video_processing.watermark_engine import WATERMARK_POSITIONS, WatermarkConfig
+
+
+class TestWatermarkPositions:
+    """水印位置枚举."""
+
+    def test_nine_positions_exist(self):
+        assert len(WATERMARK_POSITIONS) == 9
+        assert "top_left" in WATERMARK_POSITIONS
+        assert "top_center" in WATERMARK_POSITIONS
+        assert "top_right" in WATERMARK_POSITIONS
+        assert "center_left" in WATERMARK_POSITIONS
+        assert "center" in WATERMARK_POSITIONS
+        assert "center_right" in WATERMARK_POSITIONS
+        assert "bottom_left" in WATERMARK_POSITIONS
+        assert "bottom_center" in WATERMARK_POSITIONS
+        assert "bottom_right" in WATERMARK_POSITIONS
+
+    def test_position_values_are_chinese_labels(self):
+        for key, label in WATERMARK_POSITIONS.items():
+            assert isinstance(label, str)
+            assert len(label) >= 2
+
+
+class TestWatermarkConfigFromDict:
+    """from_dict 构造逻辑."""
+
+    def test_none_returns_none(self):
+        assert WatermarkConfig.from_dict(None) is None
+
+    def test_empty_dict_returns_none(self):
+        assert WatermarkConfig.from_dict({}) is None
+
+    def test_enabled_false_returns_none(self):
+        assert WatermarkConfig.from_dict({"enabled": False}) is None
+
+    def test_image_mode_without_path_returns_none(self):
+        result = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "image",
+        })
+        assert result is None
+
+    def test_image_mode_with_empty_path_returns_none(self):
+        result = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "image",
+            "image_path": "",
+        })
+        assert result is None
+
+    def test_text_mode_without_text_returns_none(self):
+        result = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "text",
+        })
+        assert result is None
+
+    def test_text_mode_with_empty_text_returns_none(self):
+        result = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "text",
+            "text": "",
+        })
+        assert result is None
+
+    def test_image_mode_success(self):
+        cfg = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "image",
+            "image_path": "/tmp/logo.png",
+            "scale": 0.3,
+            "opacity": 0.9,
+            "position": "top_left",
+            "margin_x": 30,
+            "margin_y": 30,
+        })
+        assert cfg is not None
+        assert cfg.mode == "image"
+        assert cfg.image_path == "/tmp/logo.png"
+        assert cfg.scale == 0.3
+        assert cfg.opacity == 0.9
+        assert cfg.position == "top_left"
+        assert cfg.margin_x == 30
+        assert cfg.margin_y == 30
+
+    def test_image_mode_image_key_fallback(self):
+        """image 字段作为 image_path 的 fallback."""
+        cfg = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "image",
+            "image": "/tmp/fallback.png",
+        })
+        assert cfg is not None
+        assert cfg.image_path == "/tmp/fallback.png"
+
+    def test_text_mode_success(self):
+        cfg = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "text",
+            "text": "hello world",
+            "font_size": 32,
+            "font_color": "red",
+            "position": "bottom_left",
+            "scroll": True,
+            "scroll_speed": 100,
+        })
+        assert cfg is not None
+        assert cfg.mode == "text"
+        assert cfg.text == "hello world"
+        assert cfg.font_size == 32
+        assert cfg.font_color == "red"
+        assert cfg.position == "bottom_left"
+        assert cfg.scroll is True
+        assert cfg.scroll_speed == 100
+
+    def test_invalid_position_falls_back_to_bottom_right(self):
+        cfg = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "text",
+            "text": "test",
+            "position": "invalid_position",
+        })
+        assert cfg is not None
+        assert cfg.position == "bottom_right"
+
+    def test_default_values_applied(self):
+        cfg = WatermarkConfig.from_dict({
+            "enabled": True,
+            "mode": "text",
+            "text": "test",
+        })
+        assert cfg is not None
+        assert cfg.position == "bottom_right"
+        assert cfg.opacity == 0.8
+        assert cfg.scale == 0.2
+        assert cfg.font_size == 24
+        assert cfg.font_color == "white"
+        assert cfg.margin_x == 20
+        assert cfg.margin_y == 20
+        assert cfg.scroll is False
+        assert cfg.scroll_speed == 50
+
+
+class TestWatermarkConfigValidate:
+    """validate 校验逻辑."""
+
+    def test_valid_image_config(self):
+        cfg = WatermarkConfig(
+            mode="image",
+            image_path="/tmp/logo.png",
+            position="top_right",
+            opacity=0.5,
+            scale=0.5,
+        )
+        ok, msg = cfg.validate()
+        assert ok is True
+        assert msg == ""
+
+    def test_valid_text_config(self):
+        cfg = WatermarkConfig(
+            mode="text",
+            text="hello",
+            position="center",
+            opacity=1.0,
+            font_size=48,
+        )
+        ok, msg = cfg.validate()
+        assert ok is True
+        assert msg == ""
+
+    def test_invalid_position(self):
+        cfg = WatermarkConfig(mode="text", text="test", position="nowhere")
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "不支持的位置" in msg
+
+    def test_opacity_below_zero(self):
+        cfg = WatermarkConfig(mode="text", text="test", opacity=-0.1)
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "透明度" in msg
+
+    def test_opacity_above_one(self):
+        cfg = WatermarkConfig(mode="text", text="test", opacity=1.5)
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "透明度" in msg
+
+    def test_opacity_zero_is_valid(self):
+        cfg = WatermarkConfig(mode="text", text="test", opacity=0.0)
+        ok, _ = cfg.validate()
+        assert ok is True
+
+    def test_opacity_one_is_valid(self):
+        cfg = WatermarkConfig(mode="text", text="test", opacity=1.0)
+        ok, _ = cfg.validate()
+        assert ok is True
+
+    def test_image_missing_path(self):
+        cfg = WatermarkConfig(mode="image", image_path="")
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "图片路径" in msg
+
+    def test_image_scale_too_small(self):
+        cfg = WatermarkConfig(mode="image", image_path="/tmp/a.png", scale=0.001)
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "缩放比例" in msg
+
+    def test_image_scale_too_large(self):
+        cfg = WatermarkConfig(mode="image", image_path="/tmp/a.png", scale=2.0)
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "缩放比例" in msg
+
+    def test_image_scale_boundary_valid(self):
+        cfg = WatermarkConfig(mode="image", image_path="/tmp/a.png", scale=0.01)
+        ok, _ = cfg.validate()
+        assert ok is True
+
+        cfg2 = WatermarkConfig(mode="image", image_path="/tmp/a.png", scale=1.0)
+        ok2, _ = cfg2.validate()
+        assert ok2 is True
+
+    def test_text_missing_text(self):
+        cfg = WatermarkConfig(mode="text", text="")
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "文字内容" in msg
+
+    def test_text_font_size_zero(self):
+        cfg = WatermarkConfig(mode="text", text="test", font_size=0)
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "字体大小" in msg
+
+    def test_text_font_size_negative(self):
+        cfg = WatermarkConfig(mode="text", text="test", font_size=-5)
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "字体大小" in msg
+
+    def test_unsupported_mode(self):
+        cfg = WatermarkConfig(mode="video", text="test")
+        ok, msg = cfg.validate()
+        assert ok is False
+        assert "不支持的水印模式" in msg