feat: 试用过程中的细节优化

server/services/video_renderer.py

@@ -58,11 +58,16 @@ async def _run_process(
     should_cancel: Callable[[], Awaitable[bool]],
     timeout_seconds: int,
 ) -> None:
-    process = await asyncio.create_subprocess_exec(
-        *args,
-        stdout=asyncio.subprocess.DEVNULL,
-        stderr=asyncio.subprocess.PIPE,
-    )
+    try:
+        process = await asyncio.create_subprocess_exec(
+            *args,
+            stdout=asyncio.subprocess.DEVNULL,
+            stderr=asyncio.subprocess.PIPE,
+        )
+    except FileNotFoundError as exc:
+        raise VideoRenderError(
+            f"未找到视频合成工具「{args[0]}」。请安装 FFmpeg，并配置 VIDEO_FFMPEG_PATH 为其可执行文件的绝对路径。"
+        ) from exc
     try:
         waited = 0.0
         while process.returncode is None:
@@ -91,13 +96,18 @@ async def _run_process(
 
 async def _probe(path: Path) -> dict:
     settings = get_settings()
-    process = await asyncio.create_subprocess_exec(
-        settings.video_ffprobe_path,
-        "-v", "error", "-show_entries", "format=duration,size:stream=codec_name,width,height,pix_fmt",
-        "-of", "json", str(path),
-        stdout=asyncio.subprocess.PIPE,
-        stderr=asyncio.subprocess.PIPE,
-    )
+    try:
+        process = await asyncio.create_subprocess_exec(
+            settings.video_ffprobe_path,
+            "-v", "error", "-show_entries", "format=duration,size:stream=codec_name,width,height,pix_fmt",
+            "-of", "json", str(path),
+            stdout=asyncio.subprocess.PIPE,
+            stderr=asyncio.subprocess.PIPE,
+        )
+    except FileNotFoundError as exc:
+        raise VideoRenderError(
+            f"未找到视频校验工具「{settings.video_ffprobe_path}」。请安装 FFmpeg，并配置 VIDEO_FFPROBE_PATH 为其可执行文件的绝对路径。"
+        ) from exc
     stdout, stderr = await process.communicate()
     if process.returncode != 0:
         raise VideoRenderError(f"无法校验视频输出：{stderr.decode('utf-8', errors='replace')[-400:]}")