Fix exception when _captions_base_url is not present

youtube/watch.py

@@ -175,7 +175,7 @@ def make_caption_src(info, lang, auto=False, trans_lang=None):
     if trans_lang:
         label += ' -> ' + trans_lang
     return {
-        'url': '/' + yt_data_extract.get_caption_url(info, lang, 'vtt', auto, trans_lang),
+        'url': util.prefix_url(yt_data_extract.get_caption_url(info, lang, 'vtt', auto, trans_lang)),
         'label': label,
         'srclang': trans_lang[0:2] if trans_lang else lang[0:2],
         'on': False,
@@ -215,6 +215,8 @@ def get_subtitle_sources(info):
     pref_lang (Automatic)
     pref_lang (Manual)'''
     sources = []
+    if not yt_data_extract.captions_available(info):
+        return []
     pref_lang = settings.subtitles_language
     native_video_lang = None
     if info['automatic_caption_languages']:

youtube/yt_data_extract/__init__.py

@@ -10,4 +10,4 @@
     update_with_age_restricted_info, requires_decryption,
     extract_decryption_function, decrypt_signatures, _formats,
     update_format_with_type_info, extract_hls_formats,
-    extract_watch_info_from_html)
+    extract_watch_info_from_html, captions_available)

youtube/yt_data_extract/watch_extraction.py

@@ -730,10 +730,15 @@ def extract_watch_info_from_html(watch_html):
     return extract_watch_info(fake_polymer_json)
 
 
+def captions_available(info):
+    return bool(info['_captions_base_url'])
+
 
 def get_caption_url(info, language, format, automatic=False, translation_language=None):
     '''Gets the url for captions with the given language and format. If automatic is True, get the automatic captions for that language. If translation_language is given, translate the captions from `language` to `translation_language`. If automatic is true and translation_language is given, the automatic captions will be translated.'''
     url = info['_captions_base_url']
+    if not url:
+        return None
     url += '&lang=' + language
     url += '&fmt=' + format
     if automatic: