add advanced options for captions download format

app/main.py

@@ -247,6 +247,9 @@ async def add(request):
     auto_start = post.get('auto_start')
     split_by_chapters = post.get('split_by_chapters')
     chapter_template = post.get('chapter_template')
+    subtitle_format = post.get('subtitle_format')
+    subtitle_language = post.get('subtitle_language')
+    subtitle_mode = post.get('subtitle_mode')
 
     if custom_name_prefix is None:
         custom_name_prefix = ''
@@ -260,12 +263,34 @@ async def add(request):
         split_by_chapters = False
     if chapter_template is None:
         chapter_template = config.OUTPUT_TEMPLATE_CHAPTER
+    if subtitle_format is None:
+        subtitle_format = 'ass'
+    if subtitle_language is None:
+        subtitle_language = 'en'
+    if subtitle_mode is None:
+        subtitle_mode = 'prefer_manual'
     if chapter_template and ('..' in chapter_template or chapter_template.startswith('/') or chapter_template.startswith('\\')):
         raise web.HTTPBadRequest(reason='chapter_template must not contain ".." or start with a path separator')
+    valid_subtitle_modes = {'auto_only', 'manual_only', 'prefer_manual', 'prefer_auto'}
+    if subtitle_mode not in valid_subtitle_modes:
+        raise web.HTTPBadRequest(reason=f'subtitle_mode must be one of {sorted(valid_subtitle_modes)}')
 
     playlist_item_limit = int(playlist_item_limit)
 
-    status = await dqueue.add(url, quality, format, folder, custom_name_prefix, playlist_item_limit, auto_start, split_by_chapters, chapter_template)
+    status = await dqueue.add(
+        url,
+        quality,
+        format,
+        folder,
+        custom_name_prefix,
+        playlist_item_limit,
+        auto_start,
+        split_by_chapters,
+        chapter_template,
+        subtitle_format,
+        subtitle_language,
+        subtitle_mode,
+    )
     return web.Response(text=serializer.encode(status))
 
 @routes.post(config.URL_PREFIX + 'delete')