Fix SRT subtitle conversion and default selection

src/utils/subtitles.ts

@@ -2,34 +2,57 @@
  * Parse SRT subtitle format to WebVTT
  */
 export const parseSRT = (srtContent: string): string => {
-  const lines = srtContent.trim().split('\n')
-  let vttContent = 'WEBVTT\n\n'
+  const normalised = srtContent.replace(/\r\n/g, '\n').replace(/\r/g, '\n').trim()
 
-  let i = 0
-  while (i < lines.length) {
-    // Skip subtitle number
-    if (/^\d+$/.test(lines[i].trim())) {
-      i++
-    }
-
-    // Parse timestamp line
-    if (lines[i] && lines[i].includes('-->')) {
-      const timeLine = lines[i].replace(/,/g, '.') // SRT uses comma, VTT uses dot
-      vttContent += timeLine + '\n'
-      i++
-
-      // Add subtitle text
-      while (i < lines.length && lines[i].trim() !== '') {
-        vttContent += lines[i] + '\n'
-        i++
-      }
-      vttContent += '\n'
-    }
-
-    i++
+  if (!normalised) {
+    return 'WEBVTT\n\n'
   }
 
-  return vttContent
+  const cues = normalised
+    .split(/\n{2,}/)
+    .map((cueBlock) => {
+      const lines = cueBlock
+        .split('\n')
+        .map((line) => line.replace(/^\ufeff/, '').trimEnd())
+        .filter((line, index, arr) => !(line === '' && index === arr.length - 1))
+
+      if (lines.length === 0) {
+        return null
+      }
+
+      if (/^\d+$/.test(lines[0].trim())) {
+        lines.shift()
+      }
+
+      if (lines.length === 0) {
+        return null
+      }
+
+      const timeLine = lines.shift()
+      if (!timeLine || !timeLine.includes('-->')) {
+        return null
+      }
+
+      const vttTimeLine = timeLine
+        .split('-->')
+        .map((part) => part.trim().replace(/,/g, '.'))
+        .join(' --> ')
+
+      if (!vttTimeLine.includes('-->')) {
+        return null
+      }
+
+      const text = lines.join('\n')
+      return `${vttTimeLine}\n${text}`.trim()
+    })
+    .filter((cueBlock): cueBlock is string => Boolean(cueBlock))
+
+  const header = 'WEBVTT\n\n'
+  if (cues.length === 0) {
+    return header
+  }
+
+  return header + cues.join('\n\n') + '\n'
 }
 
 /**
@@ -37,7 +60,7 @@ export const parseSRT = (srtContent: string): string => {
  */
 export const createSubtitleBlobURL = (content: string, format: 'vtt' | 'srt'): string => {
   const vttContent = format === 'srt' ? parseSRT(content) : content
-  const blob = new Blob([vttContent], { type: 'text/vtt' })
+  const blob = new Blob([vttContent], { type: 'text/vtt;charset=utf-8' })
   return URL.createObjectURL(blob)
 }