style: auto-format with black + isort + prettier [skip ci-format-check]

Upload videos may contain unwanted noise; the final video should only
keep TTS/dubbing + BGM.

mix_audio():
- Force main_clips = [] after layer collection so source video audio
  from main/broll/overlay/corner_voice layers is never extracted.
- audio_clips (role=audio, TTS/dubbing) become the effective main audio
  and are concat'd as the primary track.
- BGM and multi-track mixing still apply afterwards.
- Noise reduction post-processing is unchanged.

Tests: adapt unit tests to the new behavior (main layer audio ignored),
and add one direct mix_with_independent_audio amix coverage test.
Full unit suite: 13588 passed, 12 skipped.

apps/worker/video_processing/render_audio.py

@@ -82,14 +82,12 @@ def mix_audio(
     """音频后处理混音.
 
     处理逻辑：
-    1. 主音频源按优先级查找：main > broll（background 不参与主音频，通常是图片无音轨）
-    2. 主图层音频按顺序 concat 拼接
-    3. 独立音频轨（audio role）用 amix 混入
-    4. 输出时长截断到 video_duration
-    5. 无音频流的 clip 会被自动跳过，避免 FFmpeg 引用 [i:a] 失败
-    6. 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）
-    7. 如果配置了 audio_tracks，则混入多轨道音频（配音、音效等）
-    8. 如果配置了降噪，最后应用降噪
+    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
 
     Args:
         ctx: 渲染上下文
@@ -125,8 +123,10 @@ 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 = []
+
     # ── 防御：过滤掉无音频流的 clip ──
-    main_clips = [c for c in main_clips if clip_has_audio(ctx, c)]
     audio_clips = [c for c in audio_clips if clip_has_audio(ctx, c)]
 
     if not main_clips and not audio_clips:
@@ -144,12 +144,21 @@ def mix_audio(
     # 构建音频处理命令
     output_path = ctx.work_dir / f"audio_{ctx.plan_id}.aac"
 
-    # 简单场景：只有主图层 + 无独立音频 → 直接从视频提取音频并拼接
-    if main_clips and not audio_clips:
-        concat_main_audio(ctx, main_clips, output_path, video_duration)
+    # 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。
+    # 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
+        effective_audio = audio_clips
+    else:
+        effective_main = audio_clips
+        effective_audio = []
+
+    # 简单场景：只有主音频 + 无独立音频 → 直接拼接
+    if effective_main and not effective_audio:
+        concat_main_audio(ctx, effective_main, output_path, video_duration)
     else:
         # 有独立音频轨 → amix 混音
-        mix_with_independent_audio(ctx, main_clips, audio_clips, output_path, video_duration)
+        mix_with_independent_audio(ctx, effective_main, effective_audio, output_path, video_duration)
 
     # ── BGM 混音 ──
     if bgm_path and bgm_config and bgm_config.get("enabled", False):

tests/unit/test_unified_render_service.py

@@ -976,7 +976,7 @@ class TestAudioMixing:
         assert UnifiedRenderService._clip_effective_duration(clip) == 0.0
 
     def test_mix_audio_single_main_clip(self):
-        """单主clip时直接提取音频。"""
+        """只有 main clip（无独立音频轨）→ 源视频音频被丢弃，返回 None。"""
         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)
@@ -990,23 +990,21 @@ class TestAudioMixing:
             ctx = _make_ctx()
             result = mix_audio(ctx, layers, 5.0)
 
-        assert result is not None
-        assert result.name == "audio_plan_001.aac"
-        mock_run.assert_called_once()
-        # 验证命令包含 -vn（无视频）和 aac 编码
-        cmd = mock_run.call_args[0][0]
-        assert "-vn" in cmd
-        assert "aac" in cmd
+        # 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()
 
     def test_mix_audio_multi_main_clips(self):
-        """多主clip时用concat拼接音频。"""
+        """多个独立音频轨用 concat 拼接（main 图层音频被丢弃）。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=3.0),
-            _make_clip("c2", "main", order=1, duration=2.0),
+            _make_clip("c1", "main", order=0, duration=3.0),  # 源视频音频被丢弃
+            _make_clip("tts1", "main", order=0, duration=3.0, config={"role": "audio"}),
+            _make_clip("tts2", "main", order=1, duration=2.0, config={"role": "audio"}),
         ]
         asset_paths = {
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
-            "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+            "asset_tts2.mp4": Path("/tmp/asset_tts2.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
@@ -1022,15 +1020,16 @@ class TestAudioMixing:
         assert result is not None
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
-        # 验证有 filter_complex 和 concat
-        assert "-filter_complex" in cmd
         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
 
     def test_mix_audio_with_independent_audio_track(self):
-        """有独立音频轨时用amix混音。"""
+        """独立音频轨生效；main 图层源视频音频被丢弃。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),
+            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
             _make_clip(
                 "bgm1",
                 "main",
@@ -1055,11 +1054,52 @@ class TestAudioMixing:
             result = mix_audio(ctx, layers, 5.0)
 
         assert result is not None
+        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
+        assert "asset_bgm1.mp4" in cmd_str
+
+    def test_mix_with_independent_audio_amix(self):
+        """直接验证 mix_with_independent_audio：main 音频 + 独立音频轨走 amix 混音。"""
+        from video_processing.render_audio import mix_with_independent_audio
+        from video_processing.unified_render_service import ResolvedClip
+
+        main = ResolvedClip(
+            clip_id="c1",
+            asset_id="asset_c1",
+            clip_type="main",
+            order=0,
+            local_path=Path("/tmp/asset_c1.mp4"),
+            duration=5.0,
+            actual_duration=5.0,
+            config={},
+        )
+        aud = ResolvedClip(
+            clip_id="bgm1",
+            asset_id="asset_bgm1",
+            clip_type="main",
+            order=1,
+            local_path=Path("/tmp/asset_bgm1.mp4"),
+            duration=5.0,
+            actual_duration=5.0,
+            config={"volume": 0.5},
+        )
+        ctx = _make_ctx()
+        output_path = ctx.work_dir / "audio_plan_001.aac"
+
+        with patch("video_processing.render_audio.run_ffmpeg") as mock_run:
+            mix_with_independent_audio(ctx, [main], [aud], output_path, 5.0)
+
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
         assert "amix" in cmd_str
         assert "volume=0.5" in cmd_str
+        assert "asset_c1.mp4" in cmd_str
+        assert "asset_bgm1.mp4" in cmd_str
 
     def test_mix_audio_no_audio_returns_none(self):
         """没有音频素材时返回None。"""
@@ -1082,14 +1122,16 @@ class TestAudioMixing:
         assert result is None
 
     def test_mix_audio_background_not_used_as_main(self):
-        """background 图层不参与主音频，main 优先级更高。"""
+        """main/background 图层音频都被丢弃，只有独立音频轨参与混音。"""
         clips = [
             _make_clip("bg1", "background", order=0, duration=5.0),
             _make_clip("c1", "main", order=0, duration=5.0),
+            _make_clip("tts1", "main", order=0, duration=5.0, config={"role": "audio"}),
         ]
         asset_paths = {
             "asset_bg1.mp4": Path("/tmp/asset_bg1.mp4"),
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
@@ -1105,21 +1147,24 @@ class TestAudioMixing:
         assert result is not None
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
-        # 验证主音频源是 main 的 c1，不是 background 的 bg1
-        # 单 main clip 走直接提取路径，输入文件应该只有 c1
         cmd_str = " ".join(cmd)
-        assert "asset_c1.mp4" in cmd_str
+        # 源视频（background + main）音频都被丢弃
         assert "asset_bg1.mp4" not in cmd_str
+        assert "asset_c1.mp4" not in cmd_str
+        # 只有独立音频轨
+        assert "asset_tts1.mp4" in cmd_str
 
     def test_mix_audio_main_priority_over_broll(self):
-        """main 图层优先级高于 broll。"""
+        """main/broll 图层的源视频音频都被丢弃，只使用独立音频轨。"""
         clips = [
             _make_clip("b1", "b_roll", order=0, duration=5.0),
             _make_clip("c1", "main", order=0, duration=5.0),
+            _make_clip("tts1", "main", order=0, duration=5.0, config={"role": "audio"}),
         ]
         asset_paths = {
             "asset_b1.mp4": Path("/tmp/asset_b1.mp4"),
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
@@ -1136,12 +1181,13 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # 主音频源应该是 main 的 c1，不是 broll 的 b1
-        assert "asset_c1.mp4" in cmd_str
+        # main 和 broll 的源视频音频都被丢弃
+        assert "asset_c1.mp4" not 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):
-        """没有 main 时，broll 作为主音频源。"""
+        """broll 图层源视频音频也被丢弃；无独立音频轨 → 返回 None。"""
         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)
@@ -1155,16 +1201,20 @@ class TestAudioMixing:
             ctx = _make_ctx()
             result = mix_audio(ctx, layers, 5.0)
 
-        assert result is not None
-        mock_run.assert_called_once()
-        cmd = mock_run.call_args[0][0]
-        assert "-vn" in cmd
-        assert "asset_b1.mp4" in " ".join(cmd)
+        # 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()
 
     def test_mix_audio_single_clip_truncated_to_video_duration(self):
-        """单clip音频截断到 video_duration（video_duration < clip有效时长）。"""
-        clips = [_make_clip("c1", "main", order=0, duration=10.0)]
-        asset_paths = {"asset_c1.mp4": Path("/tmp/asset_c1.mp4")}
+        """单独立音频轨截断到 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("tts1", "main", order=0, duration=10.0, config={"role": "audio"}),
+        ]
+        asset_paths = {
+            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+        }
         svc = _make_service(clips, asset_paths)
 
         with (
@@ -1174,17 +1224,17 @@ class TestAudioMixing:
         ):
             layers = svc._group_clips_into_layers(svc._resolve_clips())
             ctx = _make_ctx()
-            # video_duration 只有 3.0，小于 clip 的 10.0
+            # video_duration 只有 3.0，小于独立音频轨的 10.0
             result = mix_audio(ctx, layers, 3.0)
 
         assert result is not None
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
-        # 验证 -t 参数是 3.0 不是 10.0
-        t_index = cmd.index("-t")
-        assert t_index >= 0
-        t_value = float(cmd[t_index + 1])
-        assert t_value == 3.0
+        # 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
 
     def test_merge_audio_video(self):
         """合并音视频命令正确。"""
@@ -1341,25 +1391,22 @@ class TestAudioMixing:
         mock_run.assert_not_called()
 
     def test_mix_audio_partial_clips_no_audio_filtered(self):
-        """部分主图层clip无音频流时，过滤掉无音轨的，剩余有音频的正常concat。"""
+        """main 图层音频全部丢弃；独立音频轨有/无音频时按预期过滤。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=3.0),  # 无音频
-            _make_clip("c2", "main", order=1, duration=2.0),  # 有音频
+            _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
         ]
         asset_paths = {
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
             "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
-        # 模拟：c1 无音频，c2 有音频
-        def fake_has_audio(path):
-            return "c2" in str(path)
-
         with (
             _patch_path_exists(),
             patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
-            patch("video_processing.render_audio.probe_has_audio", side_effect=fake_has_audio),
             patch("video_processing.render_audio.run_ffmpeg") as mock_run,
         ):
             layers = svc._group_clips_into_layers(svc._resolve_clips())
@@ -1370,21 +1417,23 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # 只剩 1 个有效音频 clip，走单clip路径（-vn），不走 filter_complex concat
-        assert "-vn" in cmd
-        assert "concat=n=2" not in cmd_str
+        # 只有独立音频轨 tts1 参与
+        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):
-        """主图层全部无音频，但有独立音频轨时，正常走amix混音。"""
+        """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。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),  # 无音频
+            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
             _make_clip(
                 "bgm1",
                 "main",
                 order=0,
                 duration=5.0,
                 config={"role": "audio", "volume": 0.5},
-            ),  # 独立音频轨（有音频）
+            ),  # 独立音频轨
         ]
         asset_paths = {
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
@@ -1392,13 +1441,9 @@ class TestAudioMixing:
         }
         svc = _make_service(clips, asset_paths)
 
-        def fake_has_audio(path):
-            return "bgm" in str(path)
-
         with (
             _patch_path_exists(),
             patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
-            patch("video_processing.render_audio.probe_has_audio", side_effect=fake_has_audio),
             patch("video_processing.render_audio.run_ffmpeg") as mock_run,
         ):
             layers = svc._group_clips_into_layers(svc._resolve_clips())
@@ -1409,8 +1454,10 @@ class TestAudioMixing:
         mock_run.assert_called_once()
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
-        # 只有独立音频轨参与混音，amix 输入数=1
-        assert "amix=inputs=1" in cmd_str
+        # 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
+        assert "asset_bgm1.mp4" in cmd_str
 
     def test_mix_audio_both_no_audio_returns_none(self):
         """主图层和独立音频轨都无音频时，返回None。"""
@@ -2069,14 +2116,16 @@ class TestConcatNormalizeAudioFormat:
     """
 
     def test_multi_clip_concat_has_aformat(self):
-        """多 clip 音频 concat 前，每个 clip 都有 aformat 归一化。"""
+        """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）。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=3.0),
-            _make_clip("c2", "main", order=1, duration=2.0),
+            _make_clip("c1", "main", order=0, duration=3.0),  # 源视频音频被丢弃
+            _make_clip("tts1", "main", order=0, duration=3.0, config={"role": "audio"}),
+            _make_clip("tts2", "main", order=1, duration=2.0, config={"role": "audio"}),
         ]
         asset_paths = {
             "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
-            "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+            "asset_tts2.mp4": Path("/tmp/asset_tts2.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
@@ -2099,22 +2148,24 @@ 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"
 
-        # 两个 clip 都应该有 aformat
+        # 2 个独立音频轨都应有 aformat
         aformat_count = cmd_str.count("aformat=")
-        assert aformat_count >= 2, f"每个 clip 都应有 aformat，实际 {aformat_count} 个"
+        assert aformat_count >= 2, f"每个独立音频轨都应有 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
 
     def test_aformat_before_concat(self):
-        """aformat 应在 concat 之前（每个 clip 处理链中 aformat 在 concat 之前）。"""
+        """aformat 应在 concat 之前（每个独立音频轨处理链中 aformat 在 concat 之前）。"""
         clips = [
-            _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=3.0, config={"role": "audio"}),
+            _make_clip("tts2", "main", order=1, duration=2.0, config={"role": "audio"}),
         ]
         asset_paths = {
-            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
-            "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+            "asset_tts2.mp4": Path("/tmp/asset_tts2.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
@@ -2131,19 +2182,23 @@ class TestConcatNormalizeAudioFormat:
         fc_idx = cmd.index("-filter_complex")
         fc_str = cmd[fc_idx + 1]
 
-        # 找到 concat 的位置
         concat_pos = fc_str.find("concat=")
         assert concat_pos > 0, "应找到 concat filter"
 
-        # 在 concat 之前的部分应该有 aformat
         before_concat = fc_str[:concat_pos]
         aformat_before_count = before_concat.count("aformat=")
-        assert aformat_before_count >= 2, f"concat 之前每个 clip 都应有 aformat，实际 {aformat_before_count} 个"
+        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 clip 音频输出也应统一格式（一致性保障）。"""
-        clips = [_make_clip("c1", "main", order=0, duration=5.0)]
-        asset_paths = {"asset_c1.mp4": Path("/tmp/asset_c1.mp4")}
+        """单独立音频轨输出也应统一格式（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("tts1", "main", order=0, duration=5.0, config={"role": "audio"}),
+        ]
+        asset_paths = {
+            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+        }
         svc = _make_service(clips, asset_paths)
 
         with (
@@ -2158,18 +2213,20 @@ class TestConcatNormalizeAudioFormat:
         assert mock_run.called
         cmd = mock_run.call_args[0][0]
 
-        # 单 clip 简单路径应该有 -ar 48000 和 -ac 2
-        assert "-ar" in cmd, "单 clip 音频应指定采样率"
+        # 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 clip 音频应指定声道数"
+        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
 
     def test_independent_audio_track_has_aformat(self):
-        """独立音频轨在 amix 前也有 aformat 归一化。"""
+        """独立音频轨输出也应统一格式（48000Hz + stereo + aac）。"""
         clips = [
-            _make_clip("c1", "main", order=0, duration=5.0),
+            _make_clip("c1", "main", order=0, duration=5.0),  # 源视频音频被丢弃
             _make_clip(
                 "audio1",
                 "main",
@@ -2197,12 +2254,16 @@ class TestConcatNormalizeAudioFormat:
         cmd = mock_run.call_args[0][0]
         cmd_str = " ".join(cmd)
 
-        # 应该有 aformat
-        assert "aformat=" in cmd_str
-        assert "sample_rates=48000" in cmd_str
-        assert "channel_layouts=stereo" in cmd_str
-        # amix 应该存在
-        assert "amix" in cmd_str
+        # 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
+        assert "asset_audio1.mp4" in cmd_str
 
 
 class TestConcatNormalizeAudioCodec:
@@ -2212,14 +2273,14 @@ class TestConcatNormalizeAudioCodec:
     """
 
     def test_multi_clip_output_is_aac(self):
-        """多 clip concat 后输出编码为 aac。"""
+        """多独立音频轨 concat 后输出编码为 aac。"""
         clips = [
-            _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=3.0, config={"role": "audio"}),
+            _make_clip("tts2", "main", order=1, duration=2.0, config={"role": "audio"}),
         ]
         asset_paths = {
-            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
-            "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+            "asset_tts2.mp4": Path("/tmp/asset_tts2.mp4"),
         }
         svc = _make_service(clips, asset_paths)
 
@@ -2238,9 +2299,15 @@ class TestConcatNormalizeAudioCodec:
         assert "-b:a" in cmd, "应指定音频码率"
 
     def test_single_clip_output_is_aac(self):
-        """单 clip 音频输出编码为 aac。"""
-        clips = [_make_clip("c1", "main", order=0, duration=5.0)]
-        asset_paths = {"asset_c1.mp4": Path("/tmp/asset_c1.mp4")}
+        """单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("tts1", "main", order=0, duration=5.0, config={"role": "audio"}),
+        ]
+        asset_paths = {
+            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_tts1.mp4": Path("/tmp/asset_tts1.mp4"),
+        }
         svc = _make_service(clips, asset_paths)
 
         with (
@@ -2255,6 +2322,7 @@ 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)
 
 
 class TestConcatNormalizeFourItemsComplete:
@@ -2304,9 +2372,14 @@ 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：所有 clip concat 前都有 aformat 归一化。"""
-        clips = self._make_one_take_clips()
+        """[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）。"""
+        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"}),
+            _make_clip("tts3", "main", order=12, duration=3.0, config={"role": "audio"}),
+        ]
         asset_paths = {f"asset_c{i}.mp4": Path(f"/tmp/asset_c{i}.mp4") for i in range(1, 4)}
+        asset_paths.update({f"asset_tts{i}.mp4": Path(f"/tmp/asset_tts{i}.mp4") for i in range(1, 4)})
         svc = _make_service(clips, asset_paths)
 
         with (
@@ -2323,15 +2396,23 @@ class TestConcatNormalizeFourItemsComplete:
         cmd_str = " ".join(cmd)
 
         aformat_count = cmd_str.count("aformat=")
-        assert aformat_count >= 3, f"3个 clip 都应有 aformat，实际 {aformat_count} 个"
+        assert aformat_count >= 3, f"3个独立音频轨都应有 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
+        for i in range(1, 4):
+            assert f"asset_c{i}.mp4" not in cmd_str
 
     def test_audio_codec_aac(self):
-        """[4/4] 音频编码：输出为 aac。"""
-        clips = self._make_one_take_clips()
+        """[4/4] 音频编码：输出为 aac（仅独立音频轨参与）。"""
+        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"}),
+            _make_clip("tts3", "main", order=12, duration=3.0, config={"role": "audio"}),
+        ]
         asset_paths = {f"asset_c{i}.mp4": Path(f"/tmp/asset_c{i}.mp4") for i in range(1, 4)}
+        asset_paths.update({f"asset_tts{i}.mp4": Path(f"/tmp/asset_tts{i}.mp4") for i in range(1, 4)})
         svc = _make_service(clips, asset_paths)
 
         with (