From 3af353eca75ee141f45a32498fade6ed8d54fb2b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=81=B5=E5=BA=94?= <lingying@coze.email>
Date: Sun, 12 Jul 2026 19:40:57 +0800
Subject: [PATCH] =?UTF-8?q?feat(unified-render):=20Phase=203=20-=20?=
 =?UTF-8?q?=E9=9F=B3=E9=A2=91=E7=BB=9F=E4=B8=80=E6=B7=B7=E9=9F=B3=20+=20?=
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- 音频后处理：主图层concat拼接 + 独立音频轨amix混音
- 音视频分离：视频先渲染无声版，音频后处理后合并
- 支持音量调节（audio clip config.volume）
- 灰度埋点：渲染开始/视频渲染完成/音频混音完成/总完成 四个阶段日志
- 新增11个音频混音单元测试
- _resolve_layer_role 支持 audio role 映射
---
 .../worker/video_processing/render_adapter.py |  21 +-
 .../unified_render_service.py                 | 349 +++++++++++++++++-
 tests/unit/test_unified_render_service.py     | 225 +++++++++++
 3 files changed, 588 insertions(+), 7 deletions(-)

diff --git a/apps/worker/video_processing/render_adapter.py b/apps/worker/video_processing/render_adapter.py
index 69d517ac3..bb24aa923 100755
--- a/apps/worker/video_processing/render_adapter.py
+++ b/apps/worker/video_processing/render_adapter.py
@@ -140,7 +140,7 @@ class RenderAdapter:
                 )
 
             logger.info(
-                "开始渲染: plan_id=%s job_id=%s ready_clips=%d",
+                "开始渲染: plan_id=%s job_id=%s ready_clips=%d engine=unified",
                 plan_id,
                 job_id,
                 len(ready_clips),
@@ -176,6 +176,18 @@ class RenderAdapter:
 
             self._report_progress(progress_cb, 100.0, "渲染完成")
 
+            logger.info(
+                "[render-adapter] render success: plan_id=%s job_id=%s engine=unified "
+                "duration=%.2fs file_size=%d resolution=%dx%d clip_count=%d",
+                plan_id,
+                job_id,
+                result.duration,
+                result.file_size,
+                result.width,
+                result.height,
+                len(ready_clips),
+            )
+
             return RenderAdapterResult(
                 success=True,
                 output_url=output_url or "",
@@ -188,7 +200,12 @@ class RenderAdapter:
             )
 
         except Exception as exc:
-            logger.exception("渲染失败: plan_id=%s", plan_id)
+            logger.exception(
+                "[render-adapter] render failed: plan_id=%s job_id=%s engine=unified error=%s",
+                plan_id,
+                job_id,
+                str(exc)[:200],
+            )
             return RenderAdapterResult(
                 success=False,
                 error_message=str(exc)[:500],
diff --git a/apps/worker/video_processing/unified_render_service.py b/apps/worker/video_processing/unified_render_service.py
index 8f2012b36..73d8ce38f 100755
--- a/apps/worker/video_processing/unified_render_service.py
+++ b/apps/worker/video_processing/unified_render_service.py
@@ -24,6 +24,7 @@ from __future__ import annotations
 import logging
 import os
 import subprocess
+import time
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Any
@@ -356,6 +357,8 @@ def _resolve_layer_role(clip_type: str, config: dict[str, Any]) -> str:
     # main type
     if role == "b_roll":
         return "broll"
+    if role == "audio":
+        return "audio"
     return "main"
 
 
@@ -415,9 +418,16 @@ class UnifiedRenderService:
         1. 视频主渲染（直通或完整链路）
         2. 如有 title/subtitle，叠加 ASS 字幕
 
+        音频后处理：
+        1. 主图层音频 concat 拼接
+        2. 独立音频轨 amix 混入
+        3. 合并到输出视频
+
         Raises:
             ValueError: 没有可渲染的片段时抛出
         """
+        t_start = time.time()
+
         # 1. 解析 clips → ResolvedClips（跳过无素材的 clip）
         resolved = self._resolve_clips()
         if not resolved:
@@ -432,18 +442,76 @@ class UnifiedRenderService:
         # 4. 生成 ASS 字幕文件（如果有 title/subtitle 配置）
         ass_path = self._maybe_generate_ass(video_duration)
 
+        # 灰度埋点：开始渲染
+        layer_roles = [l.role for l in layers]
+        clip_counts = {l.role: len(l.clips) for l in layers}
+        logger.info(
+            "[unified-render] start render: plan_id=%s clip_count=%d layers=%s clip_counts=%s",
+            self.plan.id,
+            len(resolved),
+            layer_roles,
+            clip_counts,
+        )
+
+        # 5. 视频主渲染（无声）
+        t_video_start = time.time()
+        video_only_path = self.work_dir / f"rendered_{self.plan.id}_video.mp4"
         output_path = self.work_dir / f"rendered_{self.plan.id}.mp4"
 
-        # 5. 视频主渲染
         if self._can_use_pass_through(layers):
-            self._render_pass_through(layers, output_path, ass_path=ass_path)
+            self._render_pass_through(layers, video_only_path, ass_path=ass_path)
         else:
             filter_complex, input_args = self._build_filter_complex(layers, ass_path=ass_path)
-            self._execute_ffmpeg(filter_complex, input_args, output_path)
+            self._execute_ffmpeg(filter_complex, input_args, video_only_path)
 
-        # 6. 探测输出
+        t_video_end = time.time()
+        video_render_ms = int((t_video_end - t_video_start) * 1000)
+        logger.info(
+            "[unified-render] video render done: plan_id=%s duration_ms=%d pass_through=%s",
+            self.plan.id,
+            video_render_ms,
+            self._can_use_pass_through(layers),
+        )
+
+        # 6. 音频后处理混音
+        t_audio_start = time.time()
+        audio_path = self._mix_audio(layers, video_duration)
+        t_audio_end = time.time()
+        audio_mix_ms = int((t_audio_end - t_audio_start) * 1000)
+
+        has_audio = audio_path is not None
+        if has_audio:
+            logger.info(
+                "[unified-render] audio mix done: plan_id=%s duration_ms=%d",
+                self.plan.id,
+                audio_mix_ms,
+            )
+            # 7. 合并音视频
+            self._merge_audio_video(video_only_path, audio_path, output_path)
+        else:
+            # 无音频，直接用无声视频
+            import shutil
+
+            shutil.copy2(video_only_path, output_path)
+
+        # 8. 探测输出
         duration, file_size, width, height = self._probe_output(output_path)
 
+        t_total = int((time.time() - t_start) * 1000)
+        logger.info(
+            "[unified-render] render done: plan_id=%s total_ms=%d video_ms=%d audio_ms=%d "
+            "output_duration=%.2fs output_size=%d resolution=%dx%d has_audio=%s",
+            self.plan.id,
+            t_total,
+            video_render_ms,
+            audio_mix_ms if has_audio else 0,
+            duration,
+            file_size,
+            width,
+            height,
+            has_audio,
+        )
+
         return RenderResult(
             output_path=output_path,
             duration=duration,
@@ -930,7 +998,7 @@ class UnifiedRenderService:
             raise
 
     def _probe_output(self, output_path: Path) -> tuple[float, int, int, int]:
-        """探测输出文件的时长、大小、宽高。
+        """探测输出文件的时长、大小、宽高.
 
         Returns:
             (duration, file_size, width, height)
@@ -943,3 +1011,274 @@ class UnifiedRenderService:
             info["width"],
             info["height"],
         )
+
+    # ── 音频后处理 ────────────────────────────────────────────────────────
+
+    def _mix_audio(self, layers: list[RenderLayer], video_duration: float) -> Path | None:
+        """音频后处理混音.
+
+        处理逻辑：
+        1. 主图层（main/broll/background）音频按顺序 concat 拼接
+        2. 独立音频轨（audio role）用 amix 混入
+        3. 输出时长截断到 video_duration
+
+        Args:
+            layers: 图层列表
+            video_duration: 视频总时长（用于截断音频）
+
+        Returns:
+            混音后的音频文件路径，无音频时返回 None
+        """
+        # 收集主图层的视频 clips（带音频）
+        main_clips: list[ResolvedClip] = []
+        for layer in layers:
+            if layer.role in ("main", "broll", "background"):
+                main_clips.extend(layer.clips)
+                break  # 只取第一个主图层
+
+        if not main_clips:
+            # 没有主视频图层，检查其他带音频的图层
+            for layer in layers:
+                if layer.role in ("overlay", "corner_voice"):
+                    main_clips.extend(layer.clips)
+                    break
+
+        # 收集独立音频轨
+        audio_clips: list[ResolvedClip] = []
+        for layer in layers:
+            if layer.role == "audio":
+                audio_clips.extend(layer.clips)
+
+        if not main_clips and not audio_clips:
+            return None
+
+        # 构建音频处理命令
+        output_path = self.work_dir / f"audio_{self.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:
+            self._concat_main_audio(main_clips, output_path, video_duration)
+            return output_path
+
+        # 有独立音频轨 → amix 混音
+        self._mix_with_independent_audio(main_clips, audio_clips, output_path, video_duration)
+        return output_path
+
+    def _concat_main_audio(self, clips: list[ResolvedClip], output_path: Path, video_duration: float) -> None:
+        """主图层音频 concat 拼接（对齐链路A行为）.
+
+        每个 clip 提取音频 → trim → 按顺序 concat。
+        """
+        if len(clips) == 1:
+            # 单 clip，直接提取音频
+            clip = clips[0]
+            effective_duration = self._clip_effective_duration(clip)
+            command = [
+                FFMPEG_BIN,
+                "-y",
+                "-i",
+                str(clip.local_path),
+                "-vn",
+                "-acodec",
+                "aac",
+                "-b:a",
+                "128k",
+            ]
+            if effective_duration > 0:
+                command.extend(["-t", f"{effective_duration:.3f}"])
+            command.append(str(output_path))
+            run_ffmpeg(command)
+            return
+
+        # 多 clip，用 filter_complex concat
+        input_args: list[str] = []
+        filter_parts: list[str] = []
+
+        for i, clip in enumerate(clips):
+            input_args.extend(["-i", str(clip.local_path)])
+            effective_duration = self._clip_effective_duration(clip)
+            if effective_duration > 0:
+                filter_parts.append(f"[{i}:a]atrim=0:{effective_duration:.3f},asetpts=PTS-STARTPTS[a{i}]")
+            else:
+                filter_parts.append(f"[{i}:a]asetpts=PTS-STARTPTS[a{i}]")
+
+        audio_labels = "".join(f"[a{i}]" for i in range(len(clips)))
+        filter_parts.append(f"{audio_labels}concat=n={len(clips)}:v=0:a=1[outa]")
+
+        # 截断到视频总时长
+        if video_duration > 0:
+            filter_parts.append(f"[outa]atrim=0:{video_duration:.3f}[final_audio]")
+            final_label = "final_audio"
+        else:
+            final_label = "outa"
+
+        filter_complex = ";".join(filter_parts)
+
+        command = [
+            FFMPEG_BIN,
+            "-y",
+            *input_args,
+            "-filter_complex",
+            filter_complex,
+            "-map",
+            f"[{final_label}]",
+            "-acodec",
+            "aac",
+            "-b:a",
+            "128k",
+            str(output_path),
+        ]
+        run_ffmpeg(command)
+
+    def _mix_with_independent_audio(
+        self,
+        main_clips: list[ResolvedClip],
+        audio_clips: list[ResolvedClip],
+        output_path: Path,
+        video_duration: float,
+    ) -> None:
+        """主音频 + 独立音频轨 amix 混音.
+
+        Args:
+            main_clips: 主视频 clips（提取音频后 concat）
+            audio_clips: 独立音频轨 clips
+            output_path: 输出路径
+            video_duration: 视频总时长
+        """
+        input_args: list[str] = []
+        filter_parts: list[str] = []
+        mix_labels: list[str] = []
+
+        input_idx = 0
+
+        # 1. 主图层音频 concat
+        if main_clips:
+            for clip in main_clips:
+                input_args.extend(["-i", str(clip.local_path)])
+                effective_duration = self._clip_effective_duration(clip)
+                if effective_duration > 0:
+                    filter_parts.append(
+                        f"[{input_idx}:a]atrim=0:{effective_duration:.3f},asetpts=PTS-STARTPTS[ma{input_idx}]"
+                    )
+                else:
+                    filter_parts.append(f"[{input_idx}:a]asetpts=PTS-STARTPTS[ma{input_idx}]")
+                input_idx += 1
+
+            if len(main_clips) == 1:
+                mix_labels.append("ma0")
+            else:
+                main_labels = "".join(f"[ma{i}]" for i in range(len(main_clips)))
+                filter_parts.append(f"{main_labels}concat=n={len(main_clips)}:v=0:a=1[main_audio]")
+                mix_labels.append("main_audio")
+
+        # 2. 独立音频轨
+        for j, clip in enumerate(audio_clips):
+            input_args.extend(["-i", str(clip.local_path)])
+            effective_duration = self._clip_effective_duration(clip)
+            volume = clip.config.get("volume", 1.0) if clip.config else 1.0
+            label = f"ia{j}"
+            filters = []
+            if effective_duration > 0:
+                filters.append(f"atrim=0:{effective_duration:.3f}")
+            filters.append("asetpts=PTS-STARTPTS")
+            if volume != 1.0:
+                filters.append(f"volume={volume}")
+            filter_parts.append(f"[{input_idx}:a]{','.join(filters)}[{label}]")
+            mix_labels.append(label)
+            input_idx += 1
+
+        # 3. amix 混音
+        mix_inputs = "".join(f"[{l}]" for l in mix_labels)
+        n_inputs = len(mix_labels)
+        # normalized=0 保持音量，duration=shortest 取最短
+        filter_parts.append(f"{mix_inputs}amix=inputs={n_inputs}:duration=longest:normalize=0[mixed_audio]")
+
+        # 4. 截断到视频时长
+        if video_duration > 0:
+            filter_parts.append(f"[mixed_audio]atrim=0:{video_duration:.3f}[final_audio]")
+            final_label = "final_audio"
+        else:
+            final_label = "mixed_audio"
+
+        filter_complex = ";".join(filter_parts)
+
+        command = [
+            FFMPEG_BIN,
+            "-y",
+            *input_args,
+            "-filter_complex",
+            filter_complex,
+            "-map",
+            f"[{final_label}]",
+            "-acodec",
+            "aac",
+            "-b:a",
+            "128k",
+            str(output_path),
+        ]
+
+        logger.info(
+            "音频混音: plan_id=%s main_clips=%d audio_clips=%d",
+            self.plan.id,
+            len(main_clips),
+            len(audio_clips),
+        )
+        try:
+            run_ffmpeg(command)
+        except subprocess.CalledProcessError as e:
+            logger.error(
+                "音频混音失败: plan_id=%s exit_code=%d\nfilter_complex:\n%s",
+                self.plan.id,
+                e.returncode,
+                filter_complex[:3000],
+            )
+            raise
+
+    def _merge_audio_video(self, video_path: Path, audio_path: Path, output_path: Path) -> None:
+        """将音频合并到视频中（视频流拷贝，音频直接复用）.
+
+        Args:
+            video_path: 无声视频路径
+            audio_path: 音频文件路径
+            output_path: 输出文件路径
+        """
+        command = [
+            FFMPEG_BIN,
+            "-y",
+            "-i",
+            str(video_path),
+            "-i",
+            str(audio_path),
+            "-c:v",
+            "copy",
+            "-c:a",
+            "aac",
+            "-b:a",
+            "128k",
+            "-map",
+            "0:v:0",
+            "-map",
+            "1:a:0",
+            "-shortest",
+            "-movflags",
+            "+faststart",
+            str(output_path),
+        ]
+
+        logger.info("合并音视频: plan_id=%s", self.plan.id)
+        try:
+            run_ffmpeg(command)
+        except subprocess.CalledProcessError as e:
+            logger.error(
+                "合并音视频失败: plan_id=%s exit_code=%d",
+                self.plan.id,
+                e.returncode,
+            )
+            raise
+
+    @staticmethod
+    def _clip_effective_duration(clip: ResolvedClip) -> float:
+        """计算 clip 的有效时长."""
+        if clip.duration > 0:
+            return min(clip.duration, clip.actual_duration) if clip.actual_duration > 0 else clip.duration
+        return clip.actual_duration if clip.actual_duration > 0 else 0.0
diff --git a/tests/unit/test_unified_render_service.py b/tests/unit/test_unified_render_service.py
index 2ed2d4dad..314466684 100755
--- a/tests/unit/test_unified_render_service.py
+++ b/tests/unit/test_unified_render_service.py
@@ -573,6 +573,8 @@ class TestPassThrough:
             patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
             patch.object(svc, "_render_pass_through") as mock_pass,
             patch.object(svc, "_execute_ffmpeg") as mock_exec,
+            patch.object(svc, "_mix_audio", return_value=None),
+            patch("shutil.copy2"),
             patch.object(svc, "_probe_output", return_value=(5.0, 1024, 1280, 720)),
         ):
             result = svc.render()
@@ -598,6 +600,8 @@ class TestPassThrough:
             patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
             patch.object(svc, "_render_pass_through") as mock_pass,
             patch.object(svc, "_execute_ffmpeg") as mock_exec,
+            patch.object(svc, "_mix_audio", return_value=None),
+            patch("shutil.copy2"),
             patch.object(svc, "_probe_output", return_value=(5.5, 2048, 1280, 720)),
         ):
             result = svc.render()
@@ -816,6 +820,8 @@ class TestRender:
             _patch_path_exists(),
             patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
             patch.object(svc, "_render_pass_through") as mock_pass,
+            patch.object(svc, "_mix_audio", return_value=None),
+            patch("shutil.copy2"),
             patch.object(svc, "_probe_output", return_value=(5.0, 1024, 1280, 720)),
         ):
             result = svc.render()
@@ -843,6 +849,8 @@ class TestRender:
             _patch_path_exists(),
             patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
             patch.object(svc, "_execute_ffmpeg") as mock_exec,
+            patch.object(svc, "_mix_audio", return_value=None),
+            patch("shutil.copy2"),
             patch.object(svc, "_probe_output", return_value=(5.5, 2048, 1280, 720)),
         ):
             result = svc.render()
@@ -853,3 +861,220 @@ class TestRender:
         assert result.width == 1280
         assert result.height == 720
         mock_exec.assert_called_once()
+
+
+# ── 测试音频后处理 ──────────────────────────────────────────────────────────
+
+
+class TestAudioMixing:
+    """测试音频后处理混音功能。"""
+
+    def test_clip_effective_duration_with_both(self):
+        """指定时长和实际时长都有时取较小值。"""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/c1.mp4"),
+            clip_type="main",
+            order=0,
+            duration=3.0,
+            actual_duration=5.0,
+        )
+        assert UnifiedRenderService._clip_effective_duration(clip) == 3.0
+
+    def test_clip_effective_duration_only_actual(self):
+        """只有实际时长时用实际时长。"""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/c1.mp4"),
+            clip_type="main",
+            order=0,
+            duration=0.0,
+            actual_duration=5.0,
+        )
+        assert UnifiedRenderService._clip_effective_duration(clip) == 5.0
+
+    def test_clip_effective_duration_only_specified(self):
+        """只有指定时长时用指定时长。"""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/c1.mp4"),
+            clip_type="main",
+            order=0,
+            duration=3.0,
+            actual_duration=0.0,
+        )
+        assert UnifiedRenderService._clip_effective_duration(clip) == 3.0
+
+    def test_clip_effective_duration_zero(self):
+        """都没有时返回0。"""
+        clip = ResolvedClip(
+            clip_id="c1",
+            asset_id="a1",
+            local_path=Path("/tmp/c1.mp4"),
+            clip_type="main",
+            order=0,
+            duration=0.0,
+            actual_duration=0.0,
+        )
+        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。"""
+        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)
+
+        with (
+            _patch_path_exists(),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            layers = svc._group_clips_into_layers(svc._resolve_clips())
+            result = svc._mix_audio(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
+
+    def test_mix_audio_multi_main_clips(self):
+        """多主clip时用concat拼接音频。"""
+        clips = [
+            _make_clip("c1", "main", order=0, duration=3.0),
+            _make_clip("c2", "main", order=1, duration=2.0),
+        ]
+        asset_paths = {
+            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_c2.mp4": Path("/tmp/asset_c2.mp4"),
+        }
+        svc = _make_service(clips, asset_paths)
+
+        with (
+            _patch_path_exists(),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            layers = svc._group_clips_into_layers(svc._resolve_clips())
+            result = svc._mix_audio(layers, 4.5)
+
+        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)
+        assert "concat=n=2:v=0:a=1" in cmd_str
+
+    def test_mix_audio_with_independent_audio_track(self):
+        """有独立音频轨时用amix混音。"""
+        clips = [
+            _make_clip("c1", "main", order=0, duration=5.0),
+            _make_clip(
+                "bgm1",
+                "main",
+                order=0,
+                duration=5.0,
+                config={"role": "audio", "volume": 0.5},
+            ),
+        ]
+        asset_paths = {
+            "asset_c1.mp4": Path("/tmp/asset_c1.mp4"),
+            "asset_bgm1.mp4": Path("/tmp/asset_bgm1.mp4"),
+        }
+        svc = _make_service(clips, asset_paths)
+
+        with (
+            _patch_path_exists(),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch("video_processing.unified_render_service.run_ffmpeg") as mock_run,
+        ):
+            layers = svc._group_clips_into_layers(svc._resolve_clips())
+            result = svc._mix_audio(layers, 5.0)
+
+        assert result is not None
+        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
+
+    def test_mix_audio_no_audio_returns_none(self):
+        """没有音频素材时返回None。"""
+        # 构造一个没有音频的场景（比如纯文字）
+        clips = [_make_clip("t1", "title", order=0, duration=3.0)]
+        clips[0].asset_id = ""  # 无素材
+        asset_paths: dict[str, Path] = {}
+        svc = _make_service(clips, asset_paths)
+
+        with (
+            _patch_path_exists(),
+            patch("video_processing.unified_render_service.probe_duration", return_value=3.0),
+        ):
+            # 没有素材的clip会被跳过，layers为空
+            resolved = svc._resolve_clips()
+            layers = svc._group_clips_into_layers(resolved)
+            result = svc._mix_audio(layers, 3.0)
+
+        assert result is None
+
+    def test_merge_audio_video(self):
+        """合并音视频命令正确。"""
+        svc = _make_service([], {})
+        video_path = Path("/tmp/video.mp4")
+        audio_path = Path("/tmp/audio.aac")
+        output_path = Path("/tmp/output.mp4")
+
+        with patch("video_processing.unified_render_service.run_ffmpeg") as mock_run:
+            svc._merge_audio_video(video_path, audio_path, output_path)
+
+        mock_run.assert_called_once()
+        cmd = mock_run.call_args[0][0]
+        assert "-c:v" in cmd
+        assert "copy" in cmd
+        assert "-map" in cmd
+        assert "-shortest" in cmd
+
+    def test_render_calls_audio_mixing(self):
+        """完整render流程会调用音频混音。"""
+        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)
+
+        with (
+            _patch_path_exists(),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch.object(svc, "_render_pass_through"),
+            patch.object(svc, "_mix_audio", return_value=Path("/tmp/audio.aac")) as mock_mix,
+            patch.object(svc, "_merge_audio_video") as mock_merge,
+            patch.object(svc, "_probe_output", return_value=(5.0, 1024, 1280, 720)),
+        ):
+            result = svc.render()
+
+        mock_mix.assert_called_once()
+        mock_merge.assert_called_once()
+        assert result.duration == 5.0
+
+    def test_render_without_audio_copies_video(self):
+        """无音频时直接copy视频文件。"""
+        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)
+
+        with (
+            _patch_path_exists(),
+            patch("video_processing.unified_render_service.probe_duration", return_value=5.0),
+            patch.object(svc, "_render_pass_through"),
+            patch.object(svc, "_mix_audio", return_value=None),
+            patch("shutil.copy2") as mock_copy,
+            patch.object(svc, "_probe_output", return_value=(5.0, 1024, 1280, 720)),
+        ):
+            result = svc.render()
+
+        mock_copy.assert_called_once()
+        assert result.duration == 5.0