fix(worker): render_plan 保留视频原声并尊重每clip音量

根因：render_audio.mix_audio 中 main_clips = [] 无条件丢弃主图层源视频
原声（PR #1249 "避免录入杂音"），导致走新路径 render_plan 生成的成片
没有原声，与预览不一致（用户反馈"音频没有"）。

修复：
- mix_audio 保留 main/broll 原声，按 clip.config.volume 控制音量，
  无音频流/静音(volume=0)的 clip 安全过滤
- concat_main_audio 单clip与多clip路径均应用 per-clip volume 滤镜
- 直通渲染(_render_pass_through)改为先 probe_has_audio 再决定是否编码
  音频，并应用 per-clip volume；不再无条件假设 main 带音频
- stream copy 在音量非默认时回退重编码
- 新增 _clip_volume 辅助函数(render_audio + UnifiedRenderService)
- 更新 test_unified_render_service 旧"丢弃原声"断言为新行为
- 新增 test_original_audio_retained.py 9 个回归测试

验证：161 个相关单测全部通过

apps/worker/video_processing/render_audio.py

@@ -67,6 +67,16 @@ def clip_has_audio(ctx: RenderContext, clip: ResolvedClip) -> bool:
     return ctx._audio_cache[key]
 
 
+def _clip_volume(clip: ResolvedClip) -> float:
+    """读取 clip 的音量配置（0.0~1.0，>1 放大）。缺省 1.0 原声。"""
+    cfg = getattr(clip, "config", None) or {}
+    try:
+        vol = float(cfg.get("volume", 1.0))
+    except (TypeError, ValueError):
+        return 1.0
+    return max(0.0, vol)
+
+
 # ── 音频混音 ──────────────────────────────────────────────────────────────────
 
 
@@ -82,12 +92,13 @@ def mix_audio(
     """音频后处理混音.
 
     处理逻辑：
-    1. 丢弃主图层（main/broll/overlay/corner_voice）的原始音频，避免录入源视频杂音
-    2. 仅使用独立音频轨（audio role，TTS/配音）作为主音频
-    3. 如果提供了 bgm_path，则额外混入 BGM（支持淡入淡出、循环、人声闪避）
-    4. 如果配置了 audio_tracks，则混入多轨道音频（配音、音效等）
-    5. 输出时长截断到 video_duration
-    6. 如果配置了降噪，最后应用降噪
+    1. 保留主图层（main/broll/overlay/corner_voice）视频素材的原声，按顺序 concat 拼接
+    2. 每个 clip 按 config.volume 应用音量（volume=0 静音，=1 原声）
+    3. 独立音频轨（audio role，TTS/配音）通过 amix 混入
+    4. 如果提供了 bgm_path，则额外混入 BGM（支持淡入淡出、循环、人声闪避）
+    5. 如果配置了 audio_tracks，则混入多轨道音频（配音、音效等）
+    6. 输出时长截断到 video_duration
+    7. 如果配置了降噪，最后应用降噪
 
     Args:
         ctx: 渲染上下文
@@ -123,10 +134,14 @@ def mix_audio(
     if "audio" in layer_map:
         audio_clips = layer_map["audio"].clips
 
-    # ── 丢弃源视频的原始音频（避免录入杂音），成片仅保留 TTS 配音 + BGM ──
-    main_clips = []
+    # ── 保留源视频原声：过滤掉无音频流的 main clip（图片/无声素材） ──
+    # 每个 clip 按 config.volume 控制音量（0=静音，1=原声），静音 clip 不送入 concat
+    main_clips = [
+        c for c in main_clips
+        if clip_has_audio(ctx, c) and _clip_volume(c) > 0
+    ]
 
-    # ── 防御：过滤掉无音频流的 clip ──
+    # ── 防御：过滤掉无音频流的独立音频轨 ──
     audio_clips = [c for c in audio_clips if clip_has_audio(ctx, c)]
 
     if not main_clips and not audio_clips:
@@ -144,7 +159,7 @@ def mix_audio(
     # 构建音频处理命令
     output_path = ctx.work_dir / f"audio_{ctx.plan_id}.aac"
 
-    # 源视频原始音频已被丢弃（main_clips = []），最终音频完全由独立音频轨 + BGM + 多轨配置组成。
+    # 主音频为视频素材原声 concat；独立音频轨（TTS/配音）通过 amix 混入。
     # 当无 main_clips 时，将独立音频轨作为主音频走 concat 拼接；当二者均有则走 amix 混音。
     if main_clips:
         effective_main = main_clips
@@ -282,6 +297,9 @@ def concat_main_audio(
                 "-ac",
                 "2",
             ]
+            vol = _clip_volume(clip)
+            if abs(vol - 1.0) >= 1e-6:
+                command.extend(["-af", f"volume={vol:.4f}"])
             if trim_start > 0:
                 command.extend(["-ss", f"{trim_start:.3f}"])
             if final_duration > 0:
@@ -312,6 +330,11 @@ def concat_main_audio(
                 if reverse_filter:
                     audio_filters.append(reverse_filter)
 
+            # 音量
+            vol = _clip_volume(clip)
+            if abs(vol - 1.0) >= 1e-6:
+                audio_filters.append(f"volume={vol:.4f}")
+
             # aformat 归一化：统一输出格式为 48000Hz + stereo + fltp
             audio_filters.append("aformat=sample_rates=48000:channel_layouts=stereo:sample_fmts=fltp")
 
@@ -378,6 +401,11 @@ def concat_main_audio(
             if reverse_filter:
                 audio_filters.append(reverse_filter)
 
+        # 音量（0=静音，1=原声）
+        vol = _clip_volume(clip)
+        if abs(vol - 1.0) >= 1e-6:
+            audio_filters.append(f"volume={vol:.4f}")
+
         # aformat 归一化：统一采样率48000Hz + 双声道stereo + fltp采样格式
         # concat filter 要求所有输入音频参数完全一致，否则 exit=234 失败
         audio_filters.append("aformat=sample_rates=48000:channel_layouts=stereo:sample_fmts=fltp")

apps/worker/video_processing/unified_render_service.py

@@ -36,6 +36,7 @@ from video_processing.ffmpeg_utils import (
     DEFAULT_TRANSITION_DURATION,
     FFMPEG_BIN,
     probe_duration,
+    probe_has_audio,
     probe_video_info,
     run_ffmpeg,
 )
@@ -1000,6 +1001,11 @@ class UnifiedRenderService:
         if abs(speed - 1.0) >= 1e-6:
             return False, f"有调速: speed={speed:.2f}x"
 
+        # 音量非默认（静音/放大）→ 需要音频滤镜重编码 → 不能 copy
+        vol = UnifiedRenderService._clip_volume(clip)
+        if abs(vol - 1.0) >= 1e-6:
+            return False, f"音量非默认: volume={vol:.2f}"
+
         # 有倒放 → 需要重编码 → 不能 copy
         reverse_config = ReverseConfig.from_dict(clip.config.get("reverse"))
         if reverse_config.enabled and (reverse_config.reverse_video or reverse_config.reverse_audio):
@@ -1270,12 +1276,23 @@ class UnifiedRenderService:
             "+faststart",
         ]
 
-        # 音频处理：background 通常是图片无音频，跳过；其他编码为 aac
-        # background 以外的视频素材，默认带音频
-        has_audio = role != "background"
+        # 音频处理：background 通常是图片无音频，跳过；其他角色先探测是否真有音频流。
+        # volume=0 表示该片段静音，直接丢弃音频（与多片段 mix_audio 行为一致）。
+        clip_volume = UnifiedRenderService._clip_volume(clip)
+        if role != "background" and clip_volume > 0:
+            try:
+                has_audio = probe_has_audio(clip.local_path)
+            except Exception:
+                has_audio = True
+        else:
+            has_audio = False
         if has_audio:
             af_parts: list[str] = []
 
+            # 片段音量（原声=1.0，静音已在上层排除）
+            if abs(clip_volume - 1.0) >= 1e-6:
+                af_parts.append(f"volume={clip_volume:.4f}")
+
             # 音频降噪
             try:
                 from video_processing.noise_reduction_engine import NoiseReductionConfig, NoiseReductionEngine
@@ -1976,6 +1993,16 @@ class UnifiedRenderService:
         """
         return _clip_playback_speed_pure(getattr(clip, "playback_speed", 1.0))
 
+    @staticmethod
+    def _clip_volume(clip: ResolvedClip) -> float:
+        """获取 clip 的音量（config.volume）。缺省 1.0 原声，0.0 静音。"""
+        cfg = getattr(clip, "config", None) or {}
+        try:
+            vol = float(cfg.get("volume", 1.0))
+        except (TypeError, ValueError):
+            return 1.0
+        return max(0.0, vol)
+
     @staticmethod
     def _clip_adjusted_duration(clip: ResolvedClip) -> float:
         """计算调速后的 clip 实际时长（用于拼接计算）。

tests/unit/test_original_audio_retained.py

@@ -0,0 +1,193 @@
+"""回归测试：render_plan 新路径必须保留视频素材原声。
+
+历史 Bug：mix_audio 中 `main_clips = []` 无条件丢弃源视频原声，
+导致最终生成视频没有原声（与预览不一致）。本测试钉住新行为：
+- 有音频流的 main/broll clip 原声必须进入最终音轨
+- clip.config.volume=0 静音，volume≠1.0 应用音量滤镜
+- 无音频流的素材被安全过滤
+- 直通（pass-through）路径同样尊重 probe + volume
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+from video_processing.render_audio import (
+    RenderContext,
+    _clip_volume,
+    mix_audio,
+)
+from video_processing.unified_render_service import (
+    ResolvedClip,
+    UnifiedRenderService,
+)
+
+
+def _ctx() -> RenderContext:
+    return RenderContext(work_dir=Path("/tmp/test_render_audio_fix"), plan_id="plan_audio")
+
+
+def _clip(
+    cid: str,
+    *,
+    clip_type: str = "main",
+    order: int = 0,
+    duration: float = 5.0,
+    config: dict | None = None,
+    asset: str | None = None,
+) -> ResolvedClip:
+    return ResolvedClip(
+        clip_id=cid,
+        asset_id=asset or f"asset_{cid}.mp4",
+        clip_type=clip_type,
+        order=order,
+        local_path=Path(f"/tmp/asset_{cid}.mp4"),
+        duration=duration,
+        actual_duration=duration,
+        config=config or {},
+    )
+
+
+def _layers(svc, clips):
+    # 直接把 ResolvedClip 分组为图层，跳过 _resolve_clips（后者要求原始 EditPlanClip）
+    return svc._group_clips_into_layers(clips)
+
+
+def _service(clips):
+    paths = {c.asset_id: c.local_path for c in clips}
+    return UnifiedRenderService(
+        plan=type("P", (), {"id": "plan_audio", "config": {}})(),
+        clips=clips,
+        asset_path_map=paths,
+        work_dir=Path("/tmp/test_render_audio_fix"),
+        output_width=1080,
+        output_height=1920,
+        output_fps=25,
+    )
+
+
+class TestOriginalAudioRetained:
+    """钉住原声不再被丢弃。"""
+
+    def test_single_main_clip_audio_kept(self):
+        svc = _service([_clip("c1")])
+        with (
+            patch("pathlib.Path.exists", return_value=True),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.render_audio.probe_has_audio", return_value=True),
+            patch("video_processing.render_audio.run_ffmpeg") as mock_run,
+        ):
+            result = mix_audio(_ctx(), _layers(svc, [_clip("c1")]), 5.0)
+
+        assert result is not None
+        cmd_str = " ".join(mock_run.call_args[0][0])
+        assert "asset_c1.mp4" in cmd_str
+
+    def test_multi_main_clips_concat_audio(self):
+        clips = [_clip("c1", order=0), _clip("c2", order=1)]
+        svc = _service(clips)
+        with (
+            patch("pathlib.Path.exists", return_value=True),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.render_audio.probe_has_audio", return_value=True),
+            patch("video_processing.render_audio.run_ffmpeg") as mock_run,
+        ):
+            result = mix_audio(_ctx(), _layers(svc, clips), 9.0)
+
+        assert result is not None
+        cmd_str = " ".join(mock_run.call_args[0][0])
+        assert "asset_c1.mp4" in cmd_str
+        assert "asset_c2.mp4" in cmd_str
+        assert "concat=n=2:v=0:a=1" in cmd_str
+
+    def test_main_audio_plus_independent_track_amix(self):
+        clips = [
+            _clip("c1", order=0),
+            _clip("tts1", order=1, config={"role": "audio", "volume": 0.5}),
+        ]
+        svc = _service(clips)
+        with (
+            patch("pathlib.Path.exists", return_value=True),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.render_audio.probe_has_audio", return_value=True),
+            patch("video_processing.render_audio.run_ffmpeg") as mock_run,
+        ):
+            result = mix_audio(_ctx(), _layers(svc, clips), 5.0)
+
+        assert result is not None
+        cmd_str = " ".join(mock_run.call_args[0][0])
+        assert "amix=inputs=2" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
+        assert "asset_tts1.mp4" in cmd_str
+        assert "volume=0.5" in cmd_str
+
+    def test_silent_clip_volume_zero_excluded(self):
+        """volume=0 的素材不送入原声 concat。"""
+        clips = [_clip("mute", order=0, config={"volume": 0})]
+        svc = _service(clips)
+        with (
+            patch("pathlib.Path.exists", return_value=True),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.render_audio.probe_has_audio", return_value=True),
+            patch("video_processing.render_audio.run_ffmpeg") as mock_run,
+        ):
+            result = mix_audio(_ctx(), _layers(svc, clips), 5.0)
+
+        assert result is None
+        mock_run.assert_not_called()
+
+    def test_no_audio_stream_returns_none(self):
+        clips = [_clip("c1")]
+        svc = _service(clips)
+        with (
+            patch("pathlib.Path.exists", return_value=True),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.render_audio.probe_has_audio", return_value=False),
+            patch("video_processing.render_audio.run_ffmpeg") as mock_run,
+        ):
+            result = mix_audio(_ctx(), _layers(svc, clips), 5.0)
+
+        assert result is None
+        mock_run.assert_not_called()
+
+    def test_volume_helper_default_and_override(self):
+        assert _clip_volume(_clip("c1")) == 1.0
+        assert _clip_volume(_clip("c2", config={"volume": 0.3})) == pytest.approx(0.3)
+        assert _clip_volume(_clip("c3", config={"volume": 0})) == 0.0
+
+
+class TestPassThroughAudioProbe:
+    """直通路径必须先探测音频，不能无条件假设 main 有音频。"""
+
+    def test_pass_through_probes_audio_before_encoding(self):
+        clips = [_clip("c1")]
+        svc = _service(clips)
+        with (
+            patch("pathlib.Path.exists", return_value=True),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch(
+                "video_processing.unified_render_service.probe_has_audio",
+                return_value=False,
+            ) as mock_probe,
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            layers = svc._group_clips_into_layers(clips)
+            has_audio = svc._render_pass_through(layers, Path("/tmp/out.mp4"), video_duration=5.0)
+
+        assert has_audio is False
+        mock_probe.assert_called()
+        cmd_str = " ".join(mock_run.call_args[0][0])
+        assert "aac" not in cmd_str
+
+    def test_pass_through_volume_non_default_disables_stream_copy(self):
+        svc = _service([_clip("c1", config={"volume": 0.5})])
+        clip = _clip("c1", config={"volume": 0.5})
+        can_copy, reason = svc._can_use_stream_copy(clip)
+        assert can_copy is False
+        assert "音量" in reason
+
+    def test_clip_volume_static_helper(self):
+        assert UnifiedRenderService._clip_volume(_clip("c1")) == 1.0
+        assert UnifiedRenderService._clip_volume(_clip("c2", config={"volume": 0.7})) == pytest.approx(0.7)

tests/unit/test_unified_render_service.py

@@ -60,6 +60,17 @@ class FakePlan:
     config: dict[str, Any] = field(default_factory=dict)
 
 
+@pytest.fixture(autouse=True)
+def _assume_source_clips_have_audio():
+    """默认假设测试中的视频素材都带音频流。
+
+    新行为：保留视频素材原声（不再无条件丢弃）。需要模拟无音频流的用例
+    自行 patch probe_has_audio=False（如 test_mix_audio_main_no_audio_stream_returns_none）。
+    """
+    with patch("video_processing.render_audio.probe_has_audio", return_value=True):
+        yield
+
+
 def _make_clip(
     clip_id: str,
     clip_type: str = "main",
@@ -976,7 +987,7 @@ class TestAudioMixing:
         assert UnifiedRenderService._clip_effective_duration(clip) == 0.0
 
     def test_mix_audio_single_main_clip(self):
-        """只有 main clip（无独立音频轨）→ 源视频音频被丢弃，返回 None。"""
+        """只有 main clip（无独立音频轨）→ 保留源视频原声，走单轨 concat。"""
         clips = [_make_clip("c1", "main", order=0, duration=5.0)]
         asset_paths = {"asset_c1.mp4": Path("/tmp/asset_c1.mp4")}
         svc = _make_service(clips, asset_paths)
@@ -990,14 +1001,15 @@ class TestAudioMixing:
             ctx = _make_ctx()
             result = mix_audio(ctx, layers, 5.0)
 
-        # 源视频音频被丢弃，没有独立音频轨 → 无音频
-        assert result is None
-        mock_run.assert_not_called()
+        # 保留源视频原声
+        assert result is not None
+        mock_run.assert_called_once()
+        assert "asset_c1.mp4" in " ".join(mock_run.call_args[0][0])
 
     def test_mix_audio_multi_main_clips(self):
-        """多个独立音频轨用 concat 拼接（main 图层音频被丢弃）。"""
+        """main 原声与独立音频轨通过 amix 混音。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=3.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=3.0),
             _make_clip("tts1", "main", order=0, duration=3.0, config={"role": "audio"}),
             _make_clip("tts2", "main", order=1, duration=2.0, config={"role": "audio"}),
         ]
@@ -1021,15 +1033,17 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # 2 个独立音频轨 concat
-        assert "concat=n=2:v=0:a=1" in cmd_str
-        # main 的 c1 不参与音频（源视频杂音被丢弃）
-        assert "asset_c1.mp4" not in cmd_str
+        # 原声 + 2 个独立音频轨 → amix 混音（3 路输入）
+        assert "amix=inputs=3" in cmd_str
+        # main 原声 c1 参与混音
+        assert "asset_c1.mp4" in cmd_str
+        assert "asset_tts1.mp4" in cmd_str
+        assert "asset_tts2.mp4" in cmd_str
 
     def test_mix_audio_with_independent_audio_track(self):
-        """独立音频轨生效；main 图层源视频音频被丢弃。"""
+        """main 原声与独立音频轨通过 amix 混音。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=5.0),
             _make_clip(
                 "bgm1",
                 "main",
@@ -1057,9 +1071,9 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # main 的源视频 c1 不参与音频
-        assert "asset_c1.mp4" not in cmd_str
-        # 独立音频轨 bgm1 作为最终音频生效
+        # main 原声 c1 与独立音频轨 bgm1 都参与 amix
+        assert "amix=inputs=2" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
         assert "asset_bgm1.mp4" in cmd_str
 
     def test_mix_with_independent_audio_amix(self):
@@ -1122,7 +1136,7 @@ class TestAudioMixing:
         assert result is None
 
     def test_mix_audio_background_not_used_as_main(self):
-        """main/background 图层音频都被丢弃，只有独立音频轨参与混音。"""
+        """background 图层不参与主音频；main 原声与独立音频轨混音。"""
         clips = [
             _make_clip("bg1", "background", order=0, duration=5.0),
             _make_clip("c1", "main", order=0, duration=5.0),
@@ -1148,14 +1162,15 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # 源视频（background + main）音频都被丢弃
+        # background 图层不参与主音频
         assert "asset_bg1.mp4" not in cmd_str
-        assert "asset_c1.mp4" not in cmd_str
-        # 只有独立音频轨
+        # main 原声 + 独立音频轨都参与
+        assert "amix=inputs=2" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
         assert "asset_tts1.mp4" in cmd_str
 
     def test_mix_audio_main_priority_over_broll(self):
-        """main/broll 图层的源视频音频都被丢弃，只使用独立音频轨。"""
+        """main 图层优先作为主音频，broll 不参与；与独立音频轨 amix。"""
         clips = [
             _make_clip("b1", "b_roll", order=0, duration=5.0),
             _make_clip("c1", "main", order=0, duration=5.0),
@@ -1181,13 +1196,14 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # main 和 broll 的源视频音频都被丢弃
-        assert "asset_c1.mp4" not in cmd_str
+        # main 原声 c1 优先参与；broll b1 不参与主音频
+        assert "amix=inputs=2" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
         assert "asset_b1.mp4" not in cmd_str
         assert "asset_tts1.mp4" in cmd_str
 
     def test_mix_audio_broll_used_when_no_main(self):
-        """broll 图层源视频音频也被丢弃；无独立音频轨 → 返回 None。"""
+        """无 main 图层时 broll 原声作为主音频。"""
         clips = [_make_clip("b1", "b_roll", order=0, duration=5.0)]
         asset_paths = {"asset_b1.mp4": Path("/tmp/asset_b1.mp4")}
         svc = _make_service(clips, asset_paths)
@@ -1201,14 +1217,15 @@ class TestAudioMixing:
             ctx = _make_ctx()
             result = mix_audio(ctx, layers, 5.0)
 
-        # 源视频音频被丢弃，无独立音频轨 → 无音频
-        assert result is None
-        mock_run.assert_not_called()
+        # 保留 broll 原声
+        assert result is not None
+        mock_run.assert_called_once()
+        assert "asset_b1.mp4" in " ".join(mock_run.call_args[0][0])
 
     def test_mix_audio_single_clip_truncated_to_video_duration(self):
-        """单独立音频轨截断到 video_duration（video_duration < clip有效时长）。"""
+        """主音频截断到 video_duration（video_duration < clip有效时长）。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=10.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=10.0),
             _make_clip("tts1", "main", order=0, duration=10.0, config={"role": "audio"}),
         ]
         asset_paths = {
@@ -1233,8 +1250,8 @@ class TestAudioMixing:
         # 验证截断到 3.0（-t 3.0 或 atrim=0:3.000）
         cmd_str = " ".join(cmd)
         assert "3.000" in cmd_str or "3.0" in cmd_str
-        # 源视频不参与
-        assert "asset_c1.mp4" not in cmd_str
+        # main 原声参与
+        assert "asset_c1.mp4" in cmd_str
 
     def test_merge_audio_video(self):
         """合并音视频命令正确。"""
@@ -1391,11 +1408,11 @@ class TestAudioMixing:
         mock_run.assert_not_called()
 
     def test_mix_audio_partial_clips_no_audio_filtered(self):
-        """main 图层音频全部丢弃；独立音频轨有/无音频时按预期过滤。"""
+        """main 原声正常保留；无音频流的 clip 被过滤。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=3.0),  # 源视频音频被丢弃
-            _make_clip("c2", "main", order=1, duration=2.0),  # 源视频音频被丢弃
-            _make_clip("tts1", "main", order=0, duration=2.0, config={"role": "audio"}),  # 独立音频轨
+            _make_clip("c1", "main", order=0, duration=3.0),
+            _make_clip("c2", "main", order=1, duration=2.0),
+            _make_clip("tts1", "main", order=0, duration=2.0, config={"role": "audio"}),
         ]
         asset_paths = {
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
@@ -1417,16 +1434,15 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # 只有独立音频轨 tts1 参与
+        # main 原声 c1/c2 + 独立音频轨 tts1 全部参与
+        assert "asset_c1.mp4" in cmd_str
+        assert "asset_c2.mp4" in cmd_str
         assert "asset_tts1.mp4" in cmd_str
-        # main 的 c1/c2 源视频音频被丢弃
-        assert "asset_c1.mp4" not in cmd_str
-        assert "asset_c2.mp4" not in cmd_str
 
-    def test_mix_audio_all_main_no_audio_but_independent_track(self):
-        """main 图层源视频音频全部丢弃；仅独立音频轨生效，走 concat 单轨路径。"""
+    def test_mix_audio_main_plus_independent_amix(self):
+        """main 原声与独立音频轨 amix 混音。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=5.0),
             _make_clip(
                 "bgm1",
                 "main",
@@ -1454,9 +1470,9 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # main 的源视频 c1 不参与音频
-        assert "asset_c1.mp4" not in cmd_str
-        # 只有独立音频轨 bgm1 作为主音频走单轨拼接
+        # main 原声 c1 与独立音频轨 bgm1 都参与 amix
+        assert "amix=inputs=2" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
         assert "asset_bgm1.mp4" in cmd_str
 
     def test_mix_audio_both_no_audio_returns_none(self):
@@ -2116,9 +2132,9 @@ class TestConcatNormalizeAudioFormat:
     """
 
     def test_multi_clip_concat_has_aformat(self):
-        """多独立音频轨 concat 前，每个轨都有 aformat 归一化（main 图层源视频音频被丢弃）。"""
+        """main 原声 + 独立音频轨在 concat/amix 前都有 aformat 归一化。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=3.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=3.0),
             _make_clip("tts1", "main", order=0, duration=3.0, config={"role": "audio"}),
             _make_clip("tts2", "main", order=1, duration=2.0, config={"role": "audio"}),
         ]
@@ -2148,14 +2164,14 @@ class TestConcatNormalizeAudioFormat:
         assert "channel_layouts=stereo" in cmd_str, "声道应统一为 stereo"
         assert "sample_fmts=fltp" in cmd_str, "采样格式应统一为 fltp"
 
-        # 2 个独立音频轨都应有 aformat
+        # main 原声 + 2 个独立音频轨都应有 aformat
         aformat_count = cmd_str.count("aformat=")
-        assert aformat_count >= 2, f"每个独立音频轨都应有 aformat，实际 {aformat_count} 个"
+        assert aformat_count >= 3, f"3 路音频都应有 aformat，实际 {aformat_count} 个"
 
-        # 有 concat
-        assert "concat=n=2:v=0:a=1" in cmd_str
-        # main 源视频不参与
-        assert "asset_c1.mp4" not in cmd_str
+        # amix 3 路输入
+        assert "amix=inputs=3" in cmd_str
+        # main 源视频原声参与
+        assert "asset_c1.mp4" in cmd_str
 
     def test_aformat_before_concat(self):
         """aformat 应在 concat 之前（每个独立音频轨处理链中 aformat 在 concat 之前）。"""
@@ -2190,9 +2206,9 @@ class TestConcatNormalizeAudioFormat:
         assert aformat_before_count >= 2, f"concat 之前每个独立音频轨都应有 aformat，实际 {aformat_before_count} 个"
 
     def test_single_clip_audio_has_normalized_output(self):
-        """单独立音频轨输出也应统一格式（一致性保障）。"""
+        """原声+独立音频轨输出统一格式（一致性保障）。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=5.0),
             _make_clip("tts1", "main", order=0, duration=5.0, config={"role": "audio"}),
         ]
         asset_paths = {
@@ -2212,21 +2228,20 @@ class TestConcatNormalizeAudioFormat:
 
         assert mock_run.called
         cmd = mock_run.call_args[0][0]
-
-        # 单独立音频轨简单路径应有 -ar 48000 和 -ac 2
-        assert "-ar" in cmd, "单独立音频轨应指定采样率"
-        ar_idx = cmd.index("-ar")
-        assert cmd[ar_idx + 1] == "48000", "采样率应为 48000"
-        assert "-ac" in cmd, "单独立音频轨应指定声道数"
-        ac_idx = cmd.index("-ac")
-        assert cmd[ac_idx + 1] == "2", "声道数应为 2（stereo）"
         cmd_str = " ".join(cmd)
-        assert "asset_c1.mp4" not in cmd_str
+
+        # 原声 + 独立音频轨走 amix：两路都有 aformat 归一化
+        assert "amix=inputs=2" in cmd_str
+        assert cmd_str.count("aformat=") >= 2
+        assert "sample_rates=48000" in cmd_str
+        assert "channel_layouts=stereo" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
+        assert "asset_tts1.mp4" in cmd_str
 
     def test_independent_audio_track_has_aformat(self):
-        """独立音频轨输出也应统一格式（48000Hz + stereo + aac）。"""
+        """原声+独立音频轨输出统一格式（48000Hz + stereo + aac）。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=5.0),
             _make_clip(
                 "audio1",
                 "main",
@@ -2254,15 +2269,13 @@ class TestConcatNormalizeAudioFormat:
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
 
-        # 单独立音频轨走 concat 单轨简单路径：-ar 48000 -ac 2
-        assert "-ar" in cmd
-        ar_idx = cmd.index("-ar")
-        assert cmd[ar_idx + 1] == "48000"
-        assert "-ac" in cmd
-        ac_idx = cmd.index("-ac")
-        assert cmd[ac_idx + 1] == "2"
-        # main 源视频 c1 不参与音频
-        assert "asset_c1.mp4" not in cmd_str
+        # 原声 + 独立音频轨走 amix：两路都有 aformat 归一化
+        assert "amix=inputs=2" in cmd_str
+        assert cmd_str.count("aformat=") >= 2
+        assert "sample_rates=48000" in cmd_str
+        assert "channel_layouts=stereo" in cmd_str
+        # main 原声 c1 与独立音频轨 audio1 都参与
+        assert "asset_c1.mp4" in cmd_str
         assert "asset_audio1.mp4" in cmd_str
 
 
@@ -2299,9 +2312,9 @@ class TestConcatNormalizeAudioCodec:
         assert "-b:a" in cmd, "应指定音频码率"
 
     def test_single_clip_output_is_aac(self):
-        """单独立音频轨输出编码为 aac。"""
+        """原声+独立音频轨输出编码为 aac。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
+            _make_clip("c1", "main", order=0, duration=5.0),
             _make_clip("tts1", "main", order=0, duration=5.0, config={"role": "audio"}),
         ]
         asset_paths = {
@@ -2322,7 +2335,8 @@ class TestConcatNormalizeAudioCodec:
         assert mock_run.called
         cmd = mock_run.call_args[0][0]
         assert "aac" in cmd
-        assert "asset_c1.mp4" not in " ".join(cmd)
+        # main 原声参与
+        assert "asset_c1.mp4" in " ".join(cmd)
 
 
 class TestConcatNormalizeFourItemsComplete:
@@ -2372,7 +2386,7 @@ class TestConcatNormalizeFourItemsComplete:
         assert fps_count >= 3, f"3个 clip 都应有 fps=30，实际 {fps_count} 个"
 
     def test_audio_format_normalized(self):
-        """[3/4] 音频格式：3 个独立音频轨 concat 前都有 aformat 归一化（main 图层源视频音频被丢弃）。"""
+        """[3/4] 音频格式：3 个 main 原声 + 3 个独立音频轨都有 aformat 归一化。"""
         clips = self._make_one_take_clips() + [
             _make_clip("tts1", "main", order=10, duration=5.0, config={"role": "audio"}),
             _make_clip("tts2", "main", order=11, duration=4.0, config={"role": "audio"}),
@@ -2396,13 +2410,13 @@ class TestConcatNormalizeFourItemsComplete:
         cmd_str = " ".join(cmd)
 
         aformat_count = cmd_str.count("aformat=")
-        assert aformat_count >= 3, f"3个独立音频轨都应有 aformat，实际 {aformat_count} 个"
+        assert aformat_count >= 6, f"6 路音频（3原声+3独立轨）都应有 aformat，实际 {aformat_count} 个"
         assert "sample_rates=48000" in cmd_str
         assert "channel_layouts=stereo" in cmd_str
         assert "sample_fmts=fltp" in cmd_str
-        # main 图层源视频不参与
+        # main 图层原声参与
         for i in range(1, 4):
-            assert f"asset_c{i}.mp4" not in cmd_str
+            assert f"asset_c{i}.mp4" in cmd_str
 
     def test_audio_codec_aac(self):
         """[4/4] 音频编码：输出为 aac（仅独立音频轨参与）。"""
@@ -2427,6 +2441,7 @@ class TestConcatNormalizeFourItemsComplete:
         assert mock_run.called
         cmd = mock_run.call_args[0][0]
         assert "aac" in cmd
+        # 3 个 main 原声 concat 后再与独立轨 amix
         assert "concat=n=3:v=0:a=1" in " ".join(cmd)