支持 ASS 字幕原样渲染与字幕显示设置

web/src/utils/subtitleASS.ts

@@ -0,0 +1,32 @@
+export type SubtitleChineseConverter = (text: string) => string
+
+function commaIndexAtField(line: string, fieldCount: number): number {
+  let index = -1
+  for (let field = 0; field < fieldCount; field += 1) {
+    index = line.indexOf(',', index + 1)
+    if (index < 0) return -1
+  }
+  return index
+}
+
+/**
+ * Convert only the Text column of ASS/SSA Dialogue lines. ASS styling tags,
+ * drawings, timing and positioning metadata are bytes-for-bytes preserved so
+ * the event can still be rendered by libass after a Chinese conversion.
+ */
+export function convertASSContent(
+  content: string,
+  convert: SubtitleChineseConverter,
+): string {
+  return content
+    .replace(/^\uFEFF/, '')
+    .split(/\r?\n/)
+    .map((line) => {
+      const lower = line.toLowerCase()
+      if (!lower.startsWith('dialogue:')) return line
+      const textIndex = commaIndexAtField(line, 9)
+      if (textIndex < 0) return line
+      return `${line.slice(0, textIndex + 1)}${convert(line.slice(textIndex + 1))}`
+    })
+    .join('\n')
+}