diff --git a/tests/unit/test_render_audio_utils.py b/tests/unit/test_render_audio_utils.py
new file mode 100644
index 000000000..dd24e7daa
--- /dev/null
+++ b/tests/unit/test_render_audio_utils.py
@@ -0,0 +1,107 @@
+"""
+render_audio 纯工具函数测试.
+
+覆盖 clip_effective_duration / RenderContext 等纯逻辑.
+核心混音逻辑依赖 FFmpeg，由集成测试覆盖.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+import pytest
+from video_processing.render_audio import RenderContext, clip_effective_duration
+
+
+class TestClipEffectiveDuration:
+    """clip_effective_duration 有效时长计算."""
+
+    def test_duration_specified_and_actual_longer(self):
+        """指定了 duration，且实际时长更长 → 取 duration"""
+        clip = SimpleNamespace(duration=5.0, actual_duration=10.0)
+        assert clip_effective_duration(clip) == 5.0
+
+    def test_duration_specified_and_actual_shorter(self):
+        """指定了 duration，但实际时长更短 → 取实际时长"""
+        clip = SimpleNamespace(duration=10.0, actual_duration=5.0)
+        assert clip_effective_duration(clip) == 5.0
+
+    def test_duration_specified_actual_zero(self):
+        """指定了 duration，但实际时长为 0 → 取 duration"""
+        clip = SimpleNamespace(duration=5.0, actual_duration=0.0)
+        assert clip_effective_duration(clip) == 5.0
+
+    def test_duration_specified_actual_negative(self):
+        """指定了 duration，但实际时长为负 → 取 duration"""
+        clip = SimpleNamespace(duration=5.0, actual_duration=-1.0)
+        assert clip_effective_duration(clip) == 5.0
+
+    def test_no_duration_use_actual(self):
+        """未指定 duration（0），用实际时长"""
+        clip = SimpleNamespace(duration=0.0, actual_duration=8.0)
+        assert clip_effective_duration(clip) == 8.0
+
+    def test_no_duration_negative_actual(self):
+        """未指定 duration，实际时长也为负 → 返回 0"""
+        clip = SimpleNamespace(duration=0.0, actual_duration=-5.0)
+        assert clip_effective_duration(clip) == 0.0
+
+    def test_no_duration_zero_actual(self):
+        """都为 0 → 返回 0"""
+        clip = SimpleNamespace(duration=0.0, actual_duration=0.0)
+        assert clip_effective_duration(clip) == 0.0
+
+    def test_negative_duration_use_actual(self):
+        """duration 为负（视为未指定），用实际时长"""
+        clip = SimpleNamespace(duration=-1.0, actual_duration=5.0)
+        assert clip_effective_duration(clip) == 5.0
+
+    def test_both_negative_returns_zero(self):
+        """两者都为负 → 返回 0"""
+        clip = SimpleNamespace(duration=-2.0, actual_duration=-3.0)
+        assert clip_effective_duration(clip) == 0.0
+
+    def test_exact_match(self):
+        """duration 与实际时长相等"""
+        clip = SimpleNamespace(duration=7.5, actual_duration=7.5)
+        assert clip_effective_duration(clip) == 7.5
+
+    def test_very_short_duration(self):
+        """很短的时长"""
+        clip = SimpleNamespace(duration=0.1, actual_duration=0.2)
+        assert clip_effective_duration(clip) == 0.1
+
+
+class TestRenderContext:
+    """RenderContext 渲染上下文."""
+
+    def test_create_with_work_dir_and_plan_id(self, tmp_path):
+        ctx = RenderContext(work_dir=tmp_path, plan_id="plan_123")
+        assert ctx.work_dir == tmp_path
+        assert ctx.plan_id == "plan_123"
+        assert ctx.noise_reduction_config is None
+        assert ctx._audio_cache == {}
+
+    def test_noise_reduction_config(self, tmp_path):
+        config = {"enabled": True, "strength": 0.5}
+        ctx = RenderContext(
+            work_dir=tmp_path,
+            plan_id="plan_123",
+            noise_reduction_config=config,
+        )
+        assert ctx.noise_reduction_config == config
+        assert ctx.noise_reduction_config["enabled"] is True
+
+    def test_audio_cache_isolation(self, tmp_path):
+        """每个实例有独立的缓存字典."""
+        ctx1 = RenderContext(work_dir=tmp_path, plan_id="p1")
+        ctx2 = RenderContext(work_dir=tmp_path, plan_id="p2")
+        ctx1._audio_cache["key1"] = True
+        assert "key1" not in ctx2._audio_cache
+        assert len(ctx2._audio_cache) == 0
+
+    def test_work_dir_path_type(self, tmp_path):
+        ctx = RenderContext(work_dir=tmp_path, plan_id="test")
+        assert isinstance(ctx.work_dir, Path)
diff --git a/tests/unit/test_sticker_engine.py b/tests/unit/test_sticker_engine.py
old mode 100755
new mode 100644
index d95fe07ca..bdf7f7f04
--- a/tests/unit/test_sticker_engine.py
+++ b/tests/unit/test_sticker_engine.py
@@ -1,122 +1,284 @@
-"""贴纸引擎单元测试 - 配置+解析等纯逻辑."""
+"""
+贴纸引擎配置与纯逻辑测试.
+
+覆盖 ImageStickerConfig / TextStickerConfig / _resolve_position / 常量与便捷函数.
+引擎核心滤镜生成与渲染依赖 FFmpeg，由集成测试覆盖.
+"""
 
 from __future__ import annotations
 
 import pytest
 from video_processing.sticker_engine import (
+    POSITION_PRESETS,
+    STICKER_CATEGORIES,
     ImageStickerConfig,
+    StickerEngine,
+    StickerOverlayResult,
     TextStickerConfig,
+    get_sticker_categories,
     parse_stickers_from_config,
 )
 
 
-class TestImageStickerConfigDefaults:
-    """ImageStickerConfig 默认值测试."""
+class TestStickerConstants:
+    """常量测试."""
+
+    def test_nine_position_presets(self):
+        assert len(POSITION_PRESETS) == 9
+        assert "top_left" in POSITION_PRESETS
+        assert "top_center" in POSITION_PRESETS
+        assert "top_right" in POSITION_PRESETS
+        assert "center_left" in POSITION_PRESETS
+        assert "center" in POSITION_PRESETS
+        assert "center_right" in POSITION_PRESETS
+        assert "bottom_left" in POSITION_PRESETS
+        assert "bottom_center" in POSITION_PRESETS
+        assert "bottom_right" in POSITION_PRESETS
+
+    def test_position_values_are_fractions(self):
+        for name, (x, y) in POSITION_PRESETS.items():
+            assert 0.0 <= x <= 1.0, f"{name} x={x} out of range"
+            assert 0.0 <= y <= 1.0, f"{name} y={y} out of range"
+
+    def test_sticker_categories(self):
+        assert len(STICKER_CATEGORIES) >= 3
+        for cat_id, cat_name in STICKER_CATEGORIES:
+            assert isinstance(cat_id, str)
+            assert isinstance(cat_name, str)
+            assert len(cat_id) > 0
+            assert len(cat_name) > 0
+
+
+class TestImageStickerConfig:
+    """图片贴纸配置."""
 
     def test_default_values(self):
-        """默认值正确."""
-        s = ImageStickerConfig()
-        assert s.enabled is False
-        assert s.type == "image"
-        assert s.position == "top_right"
-        assert s.x is None
-        assert s.y is None
-        assert s.x_unit == "percent"
-        assert s.y_unit == "percent"
-        assert s.scale == 1.0
-        assert s.width is None
-        assert s.height is None
-        assert s.opacity == 1.0
-        assert s.start_time == 0.0
-        assert s.duration == 0.0
-        assert s.fade_in == 0.0
-        assert s.fade_out == 0.0
-        assert s.z_index == 10
-        assert s.image_url == ""
-        assert s.preset_id == ""
+        cfg = ImageStickerConfig()
+        assert cfg.enabled is False
+        assert cfg.type == "image"
+        assert cfg.position == "top_right"
+        assert cfg.x is None
+        assert cfg.y is None
+        assert cfg.x_unit == "percent"
+        assert cfg.y_unit == "percent"
+        assert cfg.scale == 1.0
+        assert cfg.width is None
+        assert cfg.height is None
+        assert cfg.opacity == 1.0
+        assert cfg.start_time == 0.0
+        assert cfg.duration == 0.0
+        assert cfg.fade_in == 0.0
+        assert cfg.fade_out == 0.0
+        assert cfg.z_index == 10
+        assert cfg.image_url == ""
+        assert cfg.preset_id == ""
+
+    def test_custom_values(self):
+        cfg = ImageStickerConfig(
+            enabled=True,
+            position="center",
+            x=50.0,
+            y=30.0,
+            scale=0.5,
+            opacity=0.8,
+            start_time=1.0,
+            duration=5.0,
+            fade_in=0.5,
+            fade_out=0.5,
+            z_index=5,
+            image_url="/tmp/sticker.png",
+            preset_id="sticker_001",
+        )
+        assert cfg.enabled is True
+        assert cfg.position == "center"
+        assert cfg.x == 50.0
+        assert cfg.y == 30.0
+        assert cfg.scale == 0.5
+        assert cfg.opacity == 0.8
+        assert cfg.start_time == 1.0
+        assert cfg.duration == 5.0
+        assert cfg.z_index == 5
+        assert cfg.image_url == "/tmp/sticker.png"
 
 
-class TestTextStickerConfigDefaults:
-    """TextStickerConfig 默认值测试."""
+class TestTextStickerConfig:
+    """文字贴纸配置."""
 
     def test_default_values(self):
-        """默认值正确."""
-        s = TextStickerConfig()
-        assert s.enabled is False
-        assert s.type == "text"
-        assert s.text == ""
-        assert s.font_size == 36
-        assert s.font_color == "#FFFFFF"
-        assert s.font_family == "sans"
-        assert s.stroke_color == "#000000"
-        assert s.stroke_width == 2
-        assert s.shadow_color == "#000000"
-        assert s.shadow_x == 2
-        assert s.shadow_y == 2
-        assert s.shadow_alpha == 0.5
-        assert s.position == "center"
-        assert s.start_time == 0.0
-        assert s.duration == 0.0
-        assert s.z_index == 10
-        assert s.bg_color == ""
-        assert s.bg_padding == 8
-        assert s.bg_alpha == 0.8
-        assert s.bg_corner_radius == 8
+        cfg = TextStickerConfig()
+        assert cfg.enabled is False
+        assert cfg.type == "text"
+        assert cfg.text == ""
+        assert cfg.font_size == 36
+        assert cfg.font_color == "#FFFFFF"
+        assert cfg.font_family == "sans"
+        assert cfg.stroke_color == "#000000"
+        assert cfg.stroke_width == 2
+        assert cfg.shadow_color == "#000000"
+        assert cfg.shadow_x == 2
+        assert cfg.shadow_y == 2
+        assert cfg.shadow_alpha == 0.5
+        assert cfg.position == "center"
+        assert cfg.z_index == 10
+        assert cfg.bg_color == ""
+        assert cfg.bg_padding == 8
+        assert cfg.bg_alpha == 0.8
+        assert cfg.bg_corner_radius == 8
+
+    def test_custom_text_sticker(self):
+        cfg = TextStickerConfig(
+            enabled=True,
+            text="Hello",
+            font_size=48,
+            font_color="#FF0000",
+            position="bottom_center",
+            bg_color="#000000",
+            bg_padding=16,
+        )
+        assert cfg.enabled is True
+        assert cfg.text == "Hello"
+        assert cfg.font_size == 48
+        assert cfg.font_color == "#FF0000"
+        assert cfg.position == "bottom_center"
+        assert cfg.bg_color == "#000000"
+        assert cfg.bg_padding == 16
+
+
+class TestStickerOverlayResult:
+    """贴纸叠加结果."""
+
+    def test_default_values(self):
+        result = StickerOverlayResult(filter_str="overlay=10:20", output_label="[out]")
+        assert result.filter_str == "overlay=10:20"
+        assert result.output_label == "[out]"
+        assert result.extra_inputs == []
+
+    def test_with_extra_inputs(self):
+        result = StickerOverlayResult(
+            filter_str="overlay=0:0",
+            output_label="[out]",
+            extra_inputs=["/tmp/sticker.png"],
+        )
+        assert len(result.extra_inputs) == 1
+        assert result.extra_inputs[0] == "/tmp/sticker.png"
+
+
+class TestResolvePosition:
+    """_resolve_position 位置解析."""
+
+    def test_top_left_preset(self):
+        cfg = ImageStickerConfig(position="top_left")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 100, 50)
+        # top_left: (0.05, 0.05) → x = 0.05*1000 - 50 = 0, y = 0.05*500 - 25 = 0
+        assert x >= 0
+        assert y >= 0
+
+    def test_center_preset(self):
+        cfg = ImageStickerConfig(position="center")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 200, 100)
+        # center: (0.5, 0.5) → x = 500 - 100 = 400, y = 250 - 50 = 200
+        assert x == 400.0
+        assert y == 200.0
+
+    def test_bottom_right_preset(self):
+        cfg = ImageStickerConfig(position="bottom_right")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 100, 50)
+        # bottom_right: (0.95, 0.95) → x = 950 - 50 = 900, y = 475 - 25 = 450
+        assert x == 900.0
+        assert y == 450.0
+
+    def test_custom_percent_position(self):
+        cfg = ImageStickerConfig(position="center", x=25.0, y=75.0, x_unit="percent", y_unit="percent")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 100, 50)
+        # x = 0.25*1000 - 50 = 200, y = 0.75*500 - 25 = 350
+        assert x == 200.0
+        assert y == 350.0
+
+    def test_custom_pixel_position(self):
+        cfg = ImageStickerConfig(position="center", x=300, y=200, x_unit="pixel", y_unit="pixel")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 100, 50)
+        # x = 300/1000*1000 - 50 = 250, y = 200/500*500 - 25 = 175
+        # 等等，让我重新算：px = config.x / canvas_w = 300/1000 = 0.3
+        # x = px * canvas_w - sticker_w/2 = 0.3*1000 - 50 = 300 - 50 = 250
+        assert x == 250.0
+        assert y == 175.0
+
+    def test_zero_size_sticker(self):
+        cfg = ImageStickerConfig(position="center")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 0, 0)
+        # 贴纸尺寸为0时，位置就是中心点
+        assert x == 500.0
+        assert y == 250.0
+
+    def test_invalid_position_falls_back_to_center(self):
+        cfg = ImageStickerConfig(position="invalid_position")
+        x, y = StickerEngine._resolve_position(cfg, 1000, 500, 100, 50)
+        # 无效位置 → 默认居中 → x = 500 - 50 = 450, y = 250 - 25 = 225
+        assert x == 450.0
+        assert y == 225.0
+
+    def test_position_clamped_to_canvas(self):
+        # 贴纸太大，位置被钳制
+        cfg = ImageStickerConfig(position="top_left")
+        x, y = StickerEngine._resolve_position(cfg, 100, 100, 200, 200)
+        # 贴纸比画布还大，应该被钳制到 0
+        assert x >= 0
+        assert y >= 0
+        assert x <= 100
+        assert y <= 100
+
+    def test_zero_canvas_handling(self):
+        cfg = ImageStickerConfig(position="center", x=50, y=50, x_unit="pixel", y_unit="pixel")
+        x, y = StickerEngine._resolve_position(cfg, 0, 0, 10, 10)
+        # 画布为0时不应崩溃，结果被钳制到0
+        assert x == 0
+        assert y == 0
+
+    def test_text_sticker_position(self):
+        cfg = TextStickerConfig(position="top_right")
+        x, y = StickerEngine._resolve_position(cfg, 800, 400, 100, 30)
+        # top_right: (0.95, 0.05) → x = 760 - 50 = 710, 但被钳制到 canvas_w - sticker_w = 700
+        # y = 20 - 15 = 5
+        assert x == 700.0
+        assert y == 5.0
 
 
 class TestParseStickersFromConfig:
-    """parse_stickers_from_config 测试."""
+    """parse_stickers_from_config 便捷函数."""
 
     def test_none_returns_empty(self):
-        """None返回空列表."""
-        result = parse_stickers_from_config(None)
-        assert result == []
+        assert parse_stickers_from_config(None) == []
 
     def test_empty_dict_returns_empty(self):
-        """空dict返回空."""
-        result = parse_stickers_from_config({})
-        assert result == []
+        assert parse_stickers_from_config({}) == []
 
     def test_no_stickers_key_returns_empty(self):
-        """无stickers键返回空."""
-        result = parse_stickers_from_config({"other": "value"})
-        assert result == []
+        assert parse_stickers_from_config({"other": "data"}) == []
 
-    def test_stickers_not_list_returns_empty(self):
-        """stickers不是列表返回空."""
-        result = parse_stickers_from_config({"stickers": "not_a_list"})
-        assert result == []
+    def test_stickers_list_returned(self):
+        stickers = [{"type": "image", "url": "/a.png"}, {"type": "text", "text": "hi"}]
+        result = parse_stickers_from_config({"stickers": stickers})
+        assert result == stickers
+        assert len(result) == 2
+
+    def test_stickers_not_a_list_returns_empty(self):
+        assert parse_stickers_from_config({"stickers": "not_a_list"}) == []
 
     def test_empty_stickers_list(self):
-        """空贴纸列表."""
-        result = parse_stickers_from_config({"stickers": []})
-        assert result == []
+        assert parse_stickers_from_config({"stickers": []}) == []
 
-    def test_single_sticker(self):
-        """单个贴纸."""
-        result = parse_stickers_from_config(
-            {
-                "stickers": [{"type": "text", "text": "hello"}],
-            }
-        )
-        assert len(result) == 1
-        assert result[0]["text"] == "hello"
 
-    def test_multiple_stickers(self):
-        """多个贴纸."""
-        result = parse_stickers_from_config(
-            {
-                "stickers": [
-                    {"type": "text", "text": "a"},
-                    {"type": "image", "image_url": "/b.png"},
-                    {"type": "text", "text": "c"},
-                ],
-            }
-        )
-        assert len(result) == 3
+class TestGetStickerCategories:
+    """get_sticker_categories 便捷函数."""
 
-    def test_returns_raw_dicts(self):
-        """返回原始dict，不做转换."""
-        sticker = {"type": "text", "text": "test", "font_size": 48}
-        result = parse_stickers_from_config({"stickers": [sticker]})
-        assert result[0] is sticker  # 引用相同，不做深拷贝
+    def test_returns_list_of_tuples(self):
+        result = get_sticker_categories()
+        assert isinstance(result, list)
+        assert len(result) > 0
+        for item in result:
+            assert isinstance(item, tuple)
+            assert len(item) == 2
+
+    def test_matches_constant(self):
+        result = get_sticker_categories()
+        assert result == list(STICKER_CATEGORIES)
diff --git a/tests/unit/test_subtitle_render_engine.py b/tests/unit/test_subtitle_render_engine.py
index 0ad5cff84..66efa4fdc 100755
--- a/tests/unit/test_subtitle_render_engine.py
+++ b/tests/unit/test_subtitle_render_engine.py
@@ -1,9 +1,15 @@
-"""字幕渲染引擎单元测试 - 工具函数+样式配置等纯逻辑."""
+"""
+字幕渲染引擎纯函数与配置测试.
+
+覆盖 SubtitleStyle / SubtitleSegment / 颜色转换 / 时间格式化 / 文字换行 / ASS转义等纯逻辑.
+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.subtitle_render_engine import (
+    SubtitleSegment,
     SubtitleStyle,
     _escape_ass_text,
     _format_ass_time,
@@ -13,306 +19,276 @@ from video_processing.subtitle_render_engine import (
     _wrap_text,
 )
 
-# ── 颜色转换测试 ──────────────────────────────────────────────
-
 
 class TestHexToAssColor:
-    """_hex_to_ass_color 测试."""
+    """HEX → ASS 颜色转换."""
 
     def test_white(self):
-        """白色."""
         assert _hex_to_ass_color("#FFFFFF") == "&H00FFFFFF"
 
     def test_black(self):
-        """黑色."""
         assert _hex_to_ass_color("#000000") == "&H00000000"
 
     def test_red(self):
-        """红色 → BGR: 蓝绿红."""
+        # #FF0000 → R=FF, G=00, B=00 → BGR=0000FF
         assert _hex_to_ass_color("#FF0000") == "&H000000FF"
 
-    def test_green(self):
-        """绿色."""
-        assert _hex_to_ass_color("#00FF00") == "&H0000FF00"
-
     def test_blue(self):
-        """蓝色."""
+        # #0000FF → R=00, G=00, B=FF → BGR=FF0000
         assert _hex_to_ass_color("#0000FF") == "&H00FF0000"
 
-    def test_no_hash_prefix(self):
-        """不带#号."""
+    def test_green(self):
+        # #00FF00 → R=00, G=FF, B=00 → BGR=00FF00
+        assert _hex_to_ass_color("#00FF00") == "&H0000FF00"
+
+    def test_without_hash_prefix(self):
         assert _hex_to_ass_color("FF0000") == "&H000000FF"
 
-    def test_invalid_length(self):
-        """长度不对返回默认白色."""
-        assert _hex_to_ass_color("#FFF") == "&H00FFFFFF"
-        assert _hex_to_ass_color("#FF") == "&H00FFFFFF"
-        assert _hex_to_ass_color("") == "&H00FFFFFF"
+    def test_lowercase_hex(self):
+        assert _hex_to_ass_color("#ff0000") == "&H000000FF"
 
-    def test_lowercase_input(self):
-        """小写输入转为大写输出."""
-        assert _hex_to_ass_color("#aabbcc") == "&H00CCBBAA"
+    def test_mixed_case(self):
+        assert _hex_to_ass_color("#aBcDeF") == "&H00EFCDAB"
+
+    def test_invalid_length_returns_default(self):
+        assert _hex_to_ass_color("#FFF") == "&H00FFFFFF"  # 3位
+        assert _hex_to_ass_color("#FF") == "&H00FFFFFF"  # 2位
+        assert _hex_to_ass_color("#") == "&H00FFFFFF"  # 空
+
+    def test_empty_string(self):
+        assert _hex_to_ass_color("") == "&H00FFFFFF"
 
 
 class TestHexToAssBgr:
-    """_hex_to_ass_bgr 测试."""
+    """HEX → ASS BGR 部分."""
 
     def test_white(self):
-        """白色BGR."""
         assert _hex_to_ass_bgr("#FFFFFF") == "FFFFFF"
 
-    def test_red_bgr(self):
-        """红色 → BGR = 0000FF."""
+    def test_black(self):
+        assert _hex_to_ass_bgr("#000000") == "000000"
+
+    def test_red(self):
+        # #FF0000 → BGR = 0000FF
         assert _hex_to_ass_bgr("#FF0000") == "0000FF"
 
-    def test_blue_bgr(self):
-        """蓝色 → BGR = FF0000."""
+    def test_blue(self):
+        # #0000FF → BGR = FF0000
         assert _hex_to_ass_bgr("#0000FF") == "FF0000"
 
-    def test_invalid_length(self):
-        """长度不对返回默认."""
-        assert _hex_to_ass_bgr("#FF") == "FFFFFF"
+    def test_without_hash(self):
+        assert _hex_to_ass_bgr("FF0000") == "0000FF"
+
+    def test_invalid_length_returns_white(self):
+        assert _hex_to_ass_bgr("#123") == "FFFFFF"
 
 
 class TestOpacityToAssAlpha:
-    """_opacity_to_ass_alpha 测试."""
+    """不透明度 → ASS alpha."""
 
     def test_fully_opaque(self):
-        """完全不透明 → 00."""
+        # 1.0 → alpha = 255 - 255 = 0 → "00"
         assert _opacity_to_ass_alpha(1.0) == "00"
 
     def test_fully_transparent(self):
-        """完全透明 → FF."""
+        # 0.0 → alpha = 255 - 0 = 255 → "FF"
         assert _opacity_to_ass_alpha(0.0) == "FF"
 
     def test_half(self):
-        """50% → 128 → 80."""
+        # 0.5 → alpha = 255 - 127 = 128 → "80" (因为 int(0.5*255)=127)
+        # 注意：int(0.5 * 255) = 127，255-127=128 → "80"
         assert _opacity_to_ass_alpha(0.5) == "80"
 
     def test_quarter(self):
-        """75%不透明 → 64 → 40."""
+        # 0.25 → alpha = 255 - 63 = 192 → "C0"
+        assert _opacity_to_ass_alpha(0.25) == "C0"
+
+    def test_three_quarters(self):
+        # 0.75 → alpha = 255 - 191 = 64 → "40"
         assert _opacity_to_ass_alpha(0.75) == "40"
 
-
-# ── 文本处理测试 ──────────────────────────────────────────────
+    def test_zero_padded(self):
+        # 结果始终是2位十六进制
+        result = _opacity_to_ass_alpha(1.0)
+        assert len(result) == 2
+        assert result == result.upper()
 
 
 class TestEscapeAssText:
-    """_escape_ass_text 转义测试."""
+    """ASS 文本转义."""
 
-    def test_normal_text_unchanged(self):
-        """普通文本不变."""
+    def test_plain_text(self):
         assert _escape_ass_text("hello world") == "hello world"
 
-    def test_newline_converted(self):
-        """换行转成\\N."""
+    def test_newline_unix(self):
         assert _escape_ass_text("line1\nline2") == "line1\\Nline2"
 
-    def test_crlf_converted(self):
-        """\\r\\n转成\\N."""
+    def test_newline_windows(self):
         assert _escape_ass_text("line1\r\nline2") == "line1\\Nline2"
 
-    def test_carriage_return_converted(self):
-        """\\r转成\\N."""
+    def test_newline_mac(self):
         assert _escape_ass_text("line1\rline2") == "line1\\Nline2"
 
     def test_curly_braces_replaced(self):
-        """花括号替换成圆括号（ASS控制符）."""
+        # ASS 中 {} 是样式标签，需要转义
         assert _escape_ass_text("{text}") == "(text)"
 
+    def test_multiple_braces(self):
+        assert _escape_ass_text("{a}b{c}") == "(a)b(c)"
+
     def test_mixed_special_chars(self):
-        """混合特殊字符."""
-        text = "hello\n{world}\r\nend"
+        text = "line1\n{bold}\nline3"
         result = _escape_ass_text(text)
         assert "\\N" in result
+        assert "(bold)" in result
         assert "{" not in result
         assert "}" not in result
-        assert "(world)" in result
+        assert "\n" not in result
+        assert "\r" not in result
+
+    def test_empty_string(self):
+        assert _escape_ass_text("") == ""
 
 
 class TestFormatAssTime:
-    """_format_ass_time 时间格式化测试."""
+    """秒 → ASS 时间格式."""
 
     def test_zero(self):
-        """0秒."""
-        assert _format_ass_time(0) == "0:00:00.00"
+        assert _format_ass_time(0.0) == "0:00:00.00"
 
     def test_seconds_only(self):
-        """只有秒."""
         assert _format_ass_time(5.5) == "0:00:05.50"
 
-    def test_minutes_and_seconds(self):
-        """分+秒."""
-        assert _format_ass_time(125.5) == "0:02:05.50"
+    def test_minutes(self):
+        assert _format_ass_time(65.25) == "0:01:05.25"
 
-    def test_hours_minutes_seconds(self):
-        """时+分+秒."""
-        assert _format_ass_time(3725.25) == "1:02:05.25"
+    def test_hours(self):
+        assert _format_ass_time(3661.5) == "1:01:01.50"
 
-    def test_exactly_one_hour(self):
-        """刚好1小时."""
+    def test_exact_minute(self):
+        assert _format_ass_time(60.0) == "0:01:00.00"
+
+    def test_exact_hour(self):
         assert _format_ass_time(3600.0) == "1:00:00.00"
 
-    def test_single_digit_minute(self):
-        """分钟补零."""
-        result = _format_ass_time(65.0)
+    def test_sub_second_precision(self):
+        # 两位小数（厘秒精度）
+        result = _format_ass_time(1.234)
+        # 1.234 秒 = 0:00:01.23（ASS 格式是两位小数/厘秒）
+        assert result.startswith("0:00:01.")
+        # 检查秒部分是两位小数格式
         parts = result.split(":")
-        assert parts[1] == "01"
+        assert len(parts) == 3
+        sec_part = parts[2]
+        assert "." in sec_part
+        decimals = sec_part.split(".")[1]
+        assert len(decimals) == 2
 
-    def test_always_two_decimal_places(self):
-        """总是两位小数."""
-        result = _format_ass_time(3.0)
-        assert result.endswith(".00")
+    def test_negative_returns_zero_hours(self):
+        # 负数也应该能处理（虽然业务上不应该出现）
+        result = _format_ass_time(-1.0)
+        # 至少不崩溃
+        assert isinstance(result, str)
+        assert ":" in result
 
 
 class TestWrapText:
-    """_wrap_text 换行测试."""
+    """按字数换行."""
 
     def test_short_text_no_wrap(self):
-        """短文本不换行."""
-        result = _wrap_text("hello", 10)
-        assert len(result) == 1
-        assert result[0] == "hello"
+        result = _wrap_text("短文本", 10)
+        assert result == ["短文本"]
 
     def test_exact_length_no_wrap(self):
-        """刚好长度不换行."""
-        text = "abcdefghij"  # 10 chars
+        text = "一二三四五六七八九十"
         result = _wrap_text(text, 10)
         assert len(result) == 1
         assert result[0] == text
 
-    def test_simple_wrap(self):
-        """简单换行."""
-        text = "abcdefghijklmnopqrst"  # 20 chars
+    def test_long_text_wraps(self):
+        text = "一二三四五六七八九十一二三四五六七八九十"
         result = _wrap_text(text, 10)
         assert len(result) == 2
         assert len(result[0]) == 10
         assert len(result[1]) == 10
 
-    def test_uneven_wrap(self):
-        """不均等换行."""
-        text = "abcdefghijklm"  # 13 chars
-        result = _wrap_text(text, 5)
+    def test_break_on_punctuation(self):
+        # 优先在标点处断开（标点在max_chars范围内靠前位置）
+        # 共12字，max=7，句号在第6位索引，range(7,3,-1)能扫到索引5的句号
+        text = "一二三四五。六七八九十一"
+        result = _wrap_text(text, 7)
+        assert result[0] == "一二三四五。"
+        assert result[1] == "六七八九十一"
+
+    def test_break_on_comma(self):
+        text = "一二三四五，六七八九十一"
+        result = _wrap_text(text, 7)
+        assert result[0] == "一二三四五，"
+        assert result[1] == "六七八九十一"
+
+    def test_multiple_lines(self):
+        text = "一二三四五六七八九十一二三四五六七八九十一二三四五"
+        result = _wrap_text(text, 10)
         assert len(result) == 3
-        assert result[0] == "abcde"
-        assert result[1] == "fghij"
-        assert result[2] == "klm"
+        assert len(result[0]) == 10
+        assert len(result[1]) == 10
+        assert len(result[2]) == 5
 
-    def test_chinese_text_wrap(self):
-        """中文文本换行（按字符数）."""
-        text = "一二三四五六七八九十"
-        result = _wrap_text(text, 5)
-        assert len(result) == 2
-        assert result[0] == "一二三四五"
-        assert result[1] == "六七八九十"
+    def test_empty_string(self):
+        result = _wrap_text("", 10)
+        assert result == [""]
+
+    def test_max_chars_one(self):
+        # max_chars=1 时每个字符一行
+        text = "abc"
+        result = _wrap_text(text, 1)
+        assert result == ["a", "b", "c"]
+
+    def test_punctuation_at_boundary(self):
+        # 标点刚好在 max_chars 位置
+        text = "一二三四五六七八九。"
+        result = _wrap_text(text, 10)
+        assert len(result) == 1  # 刚好10个字符（含标点）
 
 
-# ── SubtitleStyle 测试 ────────────────────────────────────
+class TestSubtitleSegment:
+    """字幕片段数据类."""
+
+    def test_basic(self):
+        seg = SubtitleSegment(start=0.0, end=5.0, text="hello")
+        assert seg.start == 0.0
+        assert seg.end == 5.0
+        assert seg.text == "hello"
+
+    def test_duration(self):
+        seg = SubtitleSegment(start=1.5, end=4.5, text="test")
+        assert seg.end - seg.start == 3.0
 
 
-class TestSubtitleStyleDefaults:
-    """SubtitleStyle 默认值测试."""
+class TestSubtitleStyle:
+    """字幕样式配置."""
 
     def test_default_values(self):
-        """默认值正确."""
         style = SubtitleStyle()
         assert style.font_size > 0
-        assert style.bold is False
-        assert style.italic is False
-        assert style.stroke_enabled is True
-        assert style.shadow_enabled is False
-        assert style.background_enabled is False
-        assert style.fade_in == 0.0
-        assert style.fade_out == 0.0
-        assert style.animation_type == "none"
+        assert isinstance(style.font_color, str)
+        assert isinstance(style.background_color, str)
 
+    def test_ass_color_generation(self):
+        style = SubtitleStyle(font_color="#FFFFFF")
+        # 应该能生成 ASS 颜色格式
+        color = style.ass_font_color
+        assert isinstance(color, str)
+        assert color.startswith("&H")
 
-class TestSubtitleStyleFromDict:
-    """SubtitleStyle.from_dict 测试."""
+    def test_ass_background_color(self):
+        style = SubtitleStyle(background_color="#000000", background_opacity=0.5)
+        color = style.ass_background_color
+        assert isinstance(color, str)
+        assert color.startswith("&H")
 
-    def test_none_returns_default(self):
-        """None返回默认样式."""
-        style = SubtitleStyle.from_dict(None)
-        assert isinstance(style, SubtitleStyle)
-
-    def test_empty_dict_returns_default(self):
-        """空dict返回默认."""
-        style = SubtitleStyle.from_dict({})
-        assert isinstance(style, SubtitleStyle)
-
-    def test_custom_font_size(self):
-        """自定义字号."""
-        style = SubtitleStyle.from_dict({"size": 48})
-        assert style.font_size == 48
-
-    def test_custom_color(self):
-        """自定义颜色."""
-        style = SubtitleStyle.from_dict({"color": "#FF0000"})
-        assert style.font_color == "#FF0000"
-
-    def test_bold_enabled(self):
-        """启用粗体."""
-        style = SubtitleStyle.from_dict({"bold": True})
-        assert style.bold is True
-
-    def test_stroke_disabled(self):
-        """禁用描边."""
-        style = SubtitleStyle.from_dict({"stroke_enabled": False})
-        assert style.stroke_enabled is False
-
-    def test_background_enabled(self):
-        """启用背景框."""
-        style = SubtitleStyle.from_dict({"background_enabled": True})
-        assert style.background_enabled is True
-
-    def test_background_opacity_clamped(self):
-        """背景透明度钳制."""
-        style = SubtitleStyle.from_dict(
-            {
-                "background_enabled": True,
-                "background_opacity": 2.0,
-            }
-        )
-        assert style.background_opacity == 1.0
-
-    def test_invalid_position_falls_back(self):
-        """无效位置回退到默认."""
-        style = SubtitleStyle.from_dict({"position": "invalid_pos"})
-        # 回退到默认位置
-        assert style.position is not None
-
-    def test_fade_in_non_negative(self):
-        """淡入时长不能为负."""
-        style = SubtitleStyle.from_dict({"fade_in": -1.0})
-        assert style.fade_in == 0.0
-
-    def test_custom_animation(self):
-        """自定义动画."""
-        style = SubtitleStyle.from_dict({"animation_type": "fade"})
-        assert style.animation_type == "fade"
-
-
-class TestSubtitleStyleProperties:
-    """SubtitleStyle 属性测试."""
-
-    def test_ass_font_color_format(self):
-        """ass_font_color格式正确."""
-        style = SubtitleStyle(font_color="#FF0000")
-        result = style.ass_font_color
-        assert result.startswith("&H")
-        assert len(result) == 10  # &H + AABBGGRR = 10 chars
-
-    def test_ass_background_color_format(self):
-        """背景颜色格式正确."""
-        style = SubtitleStyle(
-            background_enabled=True,
-            background_color="#000000",
-            background_opacity=0.5,
-        )
-        result = style.ass_background_color
-        assert result.startswith("&H")
-
-    def test_alignment_is_int(self):
-        """alignment是整数."""
-        style = SubtitleStyle()
-        assert isinstance(style.alignment, int)
+    def test_opacity_affects_alpha(self):
+        style1 = SubtitleStyle(background_opacity=1.0)
+        style2 = SubtitleStyle(background_opacity=0.0)
+        # 不透明度不同，alpha 应该不同
+        assert style1.ass_background_color != style2.ass_background_color
diff --git a/tests/unit/test_tts_engine.py b/tests/unit/test_tts_engine.py
new file mode 100644
index 000000000..8cac1d17b
--- /dev/null
+++ b/tests/unit/test_tts_engine.py
@@ -0,0 +1,131 @@
+"""
+TTS 配音引擎数据类与纯逻辑测试.
+
+覆盖 VoiceoverSegment / VoiceoverResult / TtsEngine 入口判断等纯逻辑.
+TTS 合成调用依赖外部服务，由集成测试覆盖.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+from video_processing.tts_engine import TtsEngine, VoiceoverResult, VoiceoverSegment
+
+from packages.domain.tts_config import TtsConfig
+
+
+class TestVoiceoverSegment:
+    """配音片段数据类."""
+
+    def test_default_values(self):
+        seg = VoiceoverSegment(text="hello")
+        assert seg.text == "hello"
+        assert seg.start_time == 0.0
+        assert seg.end_time == 0.0
+        assert seg.audio_path is None
+        assert seg.duration == 0.0
+
+    def test_full_values(self):
+        seg = VoiceoverSegment(
+            text="hello world",
+            start_time=1.5,
+            end_time=3.0,
+            audio_path=Path("/tmp/test.wav"),
+            duration=1.5,
+        )
+        assert seg.text == "hello world"
+        assert seg.start_time == 1.5
+        assert seg.end_time == 3.0
+        assert seg.audio_path == Path("/tmp/test.wav")
+        assert seg.duration == 1.5
+
+    def test_duration_calculation(self):
+        seg = VoiceoverSegment(text="test", start_time=0.0, end_time=5.5)
+        assert seg.end_time - seg.start_time == 5.5
+
+
+class TestVoiceoverResult:
+    """配音结果数据类."""
+
+    def test_default_failure(self):
+        result = VoiceoverResult()
+        assert result.success is False
+        assert result.segments == []
+        assert result.total_duration == 0.0
+        assert result.error_message == ""
+
+    def test_success_result(self):
+        segs = [
+            VoiceoverSegment(text="hello", duration=1.0),
+            VoiceoverSegment(text="world", duration=2.0),
+        ]
+        result = VoiceoverResult(
+            success=True,
+            segments=segs,
+            total_duration=3.0,
+        )
+        assert result.success is True
+        assert len(result.segments) == 2
+        assert result.total_duration == 3.0
+        assert result.error_message == ""
+
+    def test_failure_with_message(self):
+        result = VoiceoverResult(success=False, error_message="TTS服务不可用")
+        assert result.success is False
+        assert result.error_message == "TTS服务不可用"
+
+    def test_segments_isolated_list(self):
+        """确保每个实例有独立的segments列表."""
+        r1 = VoiceoverResult()
+        r2 = VoiceoverResult()
+        r1.segments.append(VoiceoverSegment(text="test"))
+        assert len(r2.segments) == 0
+
+
+class TestTtsEngineInit:
+    """TTS 引擎初始化."""
+
+    def test_init_creates_work_dir(self, tmp_path):
+        mock_tts = MagicMock()
+        work_dir = tmp_path / "tts_work"
+        engine = TtsEngine(mock_tts, work_dir)
+        assert work_dir.exists()
+        assert work_dir.is_dir()
+
+    def test_init_with_existing_dir(self, tmp_path):
+        mock_tts = MagicMock()
+        work_dir = tmp_path / "existing"
+        work_dir.mkdir()
+        engine = TtsEngine(mock_tts, work_dir)
+        assert work_dir.exists()
+
+
+class TestTtsEngineEntryConditions:
+    """TTS 引擎入口判断逻辑（不调用真实 TTS）."""
+
+    def test_disabled_returns_failure(self, tmp_path):
+        mock_tts = MagicMock()
+        engine = TtsEngine(mock_tts, tmp_path)
+        config = TtsConfig(enabled=False, text="hello")
+        result = engine.generate_full_voiceover(config)
+        assert result.success is False
+        assert "未启用" in result.error_message or "空" in result.error_message
+        mock_tts.synthesize.assert_not_called()
+
+    def test_empty_text_returns_failure(self, tmp_path):
+        mock_tts = MagicMock()
+        engine = TtsEngine(mock_tts, tmp_path)
+        config = TtsConfig(enabled=True, text="")
+        result = engine.generate_full_voiceover(config)
+        assert result.success is False
+        mock_tts.synthesize.assert_not_called()
+
+    def test_whitespace_text_returns_failure(self, tmp_path):
+        mock_tts = MagicMock()
+        engine = TtsEngine(mock_tts, tmp_path)
+        config = TtsConfig(enabled=True, text="   ")
+        result = engine.generate_full_voiceover(config)
+        assert result.success is False
+        mock_tts.synthesize.assert_not_called()