fix: 预览标题坐标系与后端 ASS 烧录 1:1 对齐

问题：CSS 预览层硬编码 1280x720 坐标系，后端竖屏实际输出 1080x1920，
导致标题位置、字号、边距与最终渲染视频不一致，视觉上出现"标题重叠"。

修复（PreviewVideoPanel.tsx + FrontendPreviewPlayer.tsx）：
- 根据 videoRatio 动态选择后端实际分辨率：
  · 9:16 → 1080x1920
  · 16:9 → 1920x1080
  · 1:1 → 1080x1080
- 字号缩放分母从 720 改为实际 PlayResY，不设 96 上限
- 水平边距百分比分母从 1280 改为实际 PlayResX
- 垂直边距（top/bottom）按实际 PlayResY 计算百分比
- 描边宽度、阴影模糊/偏移按容器缩放比例同步放大
- FrontendPreviewPlayer 标题叠加层同时支持半角/和全角／换行
- 移除 paddingLeft/paddingRight hack，改用 left/right 边距（与 ASS MarginL/R 一致）

apps/web/src/pages/generate/components/FrontendPreviewPlayer.tsx

@@ -76,12 +76,59 @@ function buildPlaybackSegments(
 const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
   assets,
   template,
-  videoRatio: _videoRatio,
+  videoRatio,
   ready,
   voiceAudioUrl,
   titleSettings,
 }) => {
   const segments = useMemo(() => buildPlaybackSegments(assets, template), [assets, template])
+
+  // ── ASS 坐标系参数（与后端 ass_subtitle_builder.py 一致） ──
+  const TITLE_MARGIN_TOP = 60
+  const TITLE_MARGIN_BOTTOM = 60
+  const TITLE_MARGIN_SIDE = 40
+  const playRes = (() => {
+    switch (videoRatio) {
+      case "16:9":
+        return { width: 1920, height: 1080 }
+      case "1:1":
+        return { width: 1080, height: 1080 }
+      case "9:16":
+      default:
+        return { width: 1080, height: 1920 }
+    }
+  })()
+  const playerContainerRef = useRef<HTMLDivElement>(null)
+  const [containerHeight, setContainerHeight] = useState(0)
+  useEffect(() => {
+    const el = playerContainerRef.current
+    if (!el) return
+    const ro = new ResizeObserver((entries) => {
+      for (const entry of entries) {
+        const h = entry.contentRect.height
+        if (h > 0) setContainerHeight(h)
+      }
+    })
+    ro.observe(el)
+    const rect = el.getBoundingClientRect()
+    if (rect.height > 0) setContainerHeight(rect.height)
+    return () => ro.disconnect()
+  }, [])
+
+  // 标题字号按容器高度与 PlayResY 的比例缩放
+  const titleFontSizePx =
+    containerHeight > 0
+      ? ((titleSettings?.size ?? 36) / playRes.height) * containerHeight
+      : (titleSettings?.size ?? 36)
+  const titleSidePct = (TITLE_MARGIN_SIDE / playRes.width) * 100
+  const titleTopPct = (TITLE_MARGIN_TOP / playRes.height) * 100
+  const titleBottomPct = (TITLE_MARGIN_BOTTOM / playRes.height) * 100
+  // 描边/阴影也要按缩放比例放大
+  const titleScale = containerHeight > 0 ? containerHeight / playRes.height : 1
+  const titleStrokeWidth = Math.max(1, 2 * titleScale)
+  const titleShadowBlur = 4 * titleScale
+  const titleShadowOffset = 2 * titleScale
+
   // 默认走原生 video 播放（浏览器硬件解码，独立线程，不阻塞 UI）
   // WebCodecs 仅在明确需要时启用（保留代码作为兜底）
   const useWebCodecs = false
@@ -374,6 +421,7 @@ const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
 
   return (
     <div
+      ref={playerContainerRef}
       style={{
         position: "relative",
         width: "100%",
@@ -434,48 +482,55 @@ const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
           />
         ))}
 
-      {/* 标题CSS叠加层 — video fallback 路径也要渲染 */}
+      {/* 标题CSS叠加层 — 与后端 ASS 烧录坐标系 1:1 对齐 */}
       {titleSettings?.title && (
         <div
           style={{
             position: "absolute",
-            left: 0,
-            right: 0,
+            inset: 0,
             zIndex: 5,
-            display: "flex",
-            justifyContent: "center",
             pointerEvents: "none",
-            ...(titleSettings.position === "top"
-              ? { top: "10%" }
-              : titleSettings.position === "center"
-                ? { top: "50%", transform: "translateY(-50%)" }
-                : { bottom: "15%" }),
+            overflow: "hidden",
           }}
         >
-          <span
+          <div
             style={{
-              fontSize: titleSettings.size,
-              fontFamily: titleSettings.font || "思源黑体",
-              color: titleSettings.color || "#ffffff",
-              fontWeight: titleSettings.bold ? 700 : 400,
-              fontStyle: titleSettings.italic ? "italic" : "normal",
-              textShadow: [
-                titleSettings.shadow ? "0 2px 8px rgba(0,0,0,0.7)" : undefined,
-                titleSettings.stroke
-                  ? "1px 1px 0 rgba(0,0,0,0.5), -1px -1px 0 rgba(0,0,0,0.5), 1px -1px 0 rgba(0,0,0,0.5), -1px 1px 0 rgba(0,0,0,0.5)"
-                  : undefined,
-                "0 1px 3px rgba(0,0,0,0.4)",
-              ]
-                .filter(Boolean)
-                .join(", "),
-              maxWidth: "90%",
+              position: "absolute",
+              left: `${titleSidePct}%`,
+              right: `${titleSidePct}%`,
               textAlign: "center",
-              lineHeight: 1.3,
-              wordBreak: "break-word",
+              ...(titleSettings.position === "top"
+                ? { top: `${titleTopPct}%` }
+                : titleSettings.position === "center"
+                  ? { top: "50%", transform: "translateY(-50%)" }
+                  : { bottom: `${titleBottomPct}%` }),
             }}
           >
-            {titleSettings.title}
-          </span>
+            <span
+              style={{
+                fontSize: `${titleFontSizePx}px`,
+                fontFamily: titleSettings.font || "思源黑体",
+                color: titleSettings.color || "#ffffff",
+                fontWeight: titleSettings.bold ? 700 : 400,
+                fontStyle: titleSettings.italic ? "italic" : "normal",
+                lineHeight: 1.3,
+                wordBreak: "break-word",
+                WebkitTextStroke: titleSettings.stroke
+                  ? `${titleStrokeWidth}px #000000`
+                  : undefined,
+                textShadow: titleSettings.shadow
+                  ? `${titleShadowOffset}px ${titleShadowOffset}px ${titleShadowBlur}px rgba(0,0,0,0.8)`
+                  : undefined,
+              }}
+            >
+              {titleSettings.title.split(/[/／]/).map((part, i) => (
+                <span key={i}>
+                  {i > 0 && <br />}
+                  {part}
+                </span>
+              ))}
+            </span>
+          </div>
         </div>
       )}
 

apps/web/src/pages/generate/components/PreviewVideoPanel.tsx

@@ -40,17 +40,33 @@ interface PreviewVideoPanelProps {
 }
 
 /* ── ASS 坐标系参数（与后端 ass_subtitle_builder.py 一致） ── */
-const ASS_VIDEO_HEIGHT = 720
-const ASS_TITLE_MARGIN_TOP = 60
-const ASS_TITLE_MARGIN_BOTTOM = 60
-const ASS_TITLE_MARGIN_SIDE = 40
+const TITLE_MARGIN_TOP = 60
+const TITLE_MARGIN_BOTTOM = 60
+const TITLE_MARGIN_SIDE = 40
 
-function getPositionStyle(position: string): React.CSSProperties {
-  const sidePercent = (ASS_TITLE_MARGIN_SIDE / 1280) * 100
+/** 根据视频比例返回后端实际渲染分辨率（PlayResX × PlayResY） */
+function getResolution(ratio: string): { width: number; height: number } {
+  switch (ratio) {
+    case "16:9":
+      return { width: 1920, height: 1080 }
+    case "1:1":
+      return { width: 1080, height: 1080 }
+    case "9:16":
+    default:
+      return { width: 1080, height: 1920 }
+  }
+}
+
+function getPositionStyle(
+  position: string,
+  playResX: number,
+  playResY: number,
+): React.CSSProperties {
+  const sidePercent = (TITLE_MARGIN_SIDE / playResX) * 100
   switch (position) {
     case "bottom":
       return {
-        bottom: `${(ASS_TITLE_MARGIN_BOTTOM / ASS_VIDEO_HEIGHT) * 100}%`,
+        bottom: `${(TITLE_MARGIN_BOTTOM / playResY) * 100}%`,
         left: `${sidePercent}%`,
         right: `${sidePercent}%`,
         textAlign: "center",
@@ -66,7 +82,7 @@ function getPositionStyle(position: string): React.CSSProperties {
     case "top":
     default:
       return {
-        top: `${(ASS_TITLE_MARGIN_TOP / ASS_VIDEO_HEIGHT) * 100}%`,
+        top: `${(TITLE_MARGIN_TOP / playResY) * 100}%`,
         left: `${sidePercent}%`,
         right: `${sidePercent}%`,
         textAlign: "center",
@@ -74,11 +90,16 @@ function getPositionStyle(position: string): React.CSSProperties {
   }
 }
 
-function buildTitleStyle(settings: TitleSettings, containerHeight: number): React.CSSProperties {
+function buildTitleStyle(
+  settings: TitleSettings,
+  containerHeight: number,
+  playResY: number,
+): React.CSSProperties {
+  // 字号按容器高度与 PlayResY 的比例缩放，不设上限（与后端一致）
   const fontSizePx =
     containerHeight > 0
-      ? (Math.min(settings.size, 96) / ASS_VIDEO_HEIGHT) * containerHeight
-      : (Math.min(settings.size, 96) / ASS_VIDEO_HEIGHT) * 400
+      ? (settings.size / playResY) * containerHeight
+      : (settings.size / playResY) * 400
 
   const base: React.CSSProperties = {
     fontFamily: getFontFamily(settings.font),
@@ -90,8 +111,6 @@ function buildTitleStyle(settings: TitleSettings, containerHeight: number): Reac
     wordBreak: "break-word",
     pointerEvents: "none",
     userSelect: "none",
-    paddingLeft: `${(ASS_TITLE_MARGIN_SIDE / 1280) * 100}%`,
-    paddingRight: `${(ASS_TITLE_MARGIN_SIDE / 1280) * 100}%`,
   }
   if (settings.stroke) base.WebkitTextStroke = "1px #000000"
   if (settings.shadow) base.textShadow = "2px 2px 4px rgba(0,0,0,0.8)"
@@ -99,7 +118,10 @@ function buildTitleStyle(settings: TitleSettings, containerHeight: number): Reac
 }
 
 /** CSS 标题实时预览覆盖层 */
-const TitleOverlay: React.FC<{ titleSettings: TitleSettings }> = ({ titleSettings }) => {
+const TitleOverlay: React.FC<{ titleSettings: TitleSettings; videoRatio: string }> = ({
+  titleSettings,
+  videoRatio,
+}) => {
   const containerRef = useRef<HTMLDivElement>(null)
   const [containerHeight, setContainerHeight] = useState(400)
 
@@ -118,12 +140,15 @@ const TitleOverlay: React.FC<{ titleSettings: TitleSettings }> = ({ titleSetting
     return () => ro.disconnect()
   }, [])
 
+  const { width: playResX, height: playResY } = getResolution(videoRatio)
+
   const positionStyle = useMemo(
-    () => getPositionStyle(titleSettings.position),
-    [titleSettings.position],
+    () => getPositionStyle(titleSettings.position, playResX, playResY),
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [titleSettings.position, playResX, playResY],
   )
   const titleStyle = useMemo(
-    () => buildTitleStyle(titleSettings, containerHeight),
+    () => buildTitleStyle(titleSettings, containerHeight, playResY),
     // eslint-disable-next-line react-hooks/exhaustive-deps
     [
       containerHeight,
@@ -134,6 +159,7 @@ const TitleOverlay: React.FC<{ titleSettings: TitleSettings }> = ({ titleSetting
       titleSettings.italic,
       titleSettings.stroke,
       titleSettings.shadow,
+      playResY,
     ],
   )
 
@@ -266,7 +292,9 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
         )}
 
         {/* 标题样式实时预览层（仅在有视频时叠加） */}
-        {isReady && titleSettings && <TitleOverlay titleSettings={titleSettings} />}
+        {isReady && titleSettings && (
+          <TitleOverlay titleSettings={titleSettings} videoRatio={videoRatio} />
+        )}
 
         {/* stale 遮罩：配置变更提示 */}
         {isStale && (