[udemy] Fix subtitles extraction (closes #13812)

youtube_dl/extractor/udemy.py

@@ -15,6 +15,7 @@ from ..utils import (
     ExtractorError,
     float_or_none,
     int_or_none,
+    js_to_json,
     sanitized_Request,
     unescapeHTML,
     urlencode_postdata,
@@ -268,6 +269,25 @@ class UdemyIE(InfoExtractor):
                     f = add_output_format_meta(f, format_id)
                 formats.append(f)
 
+        def extract_subtitles(track_list):
+            if not isinstance(track_list, list):
+                return
+            for track in track_list:
+                if not isinstance(track, dict):
+                    continue
+                if track.get('kind') != 'captions':
+                    continue
+                src = track.get('src')
+                if not src or not isinstance(src, compat_str):
+                    continue
+                lang = track.get('language') or track.get(
+                    'srclang') or track.get('label')
+                sub_dict = automatic_captions if track.get(
+                    'autogenerated') is True else subtitles
+                sub_dict.setdefault(lang, []).append({
+                    'url': src,
+                })
+
         download_urls = asset.get('download_urls')
         if isinstance(download_urls, dict):
             extract_formats(download_urls.get('Video'))
@@ -315,23 +335,16 @@ class UdemyIE(InfoExtractor):
                 extract_formats(data.get('sources'))
                 if not duration:
                     duration = int_or_none(data.get('duration'))
-                tracks = data.get('tracks')
-                if isinstance(tracks, list):
-                    for track in tracks:
-                        if not isinstance(track, dict):
-                            continue
-                        if track.get('kind') != 'captions':
-                            continue
-                        src = track.get('src')
-                        if not src or not isinstance(src, compat_str):
-                            continue
-                        lang = track.get('language') or track.get(
-                            'srclang') or track.get('label')
-                        sub_dict = automatic_captions if track.get(
-                            'autogenerated') is True else subtitles
-                        sub_dict.setdefault(lang, []).append({
-                            'url': src,
-                        })
+                extract_subtitles(data.get('tracks'))
+
+            if not subtitles and not automatic_captions:
+                text_tracks = self._parse_json(
+                    self._search_regex(
+                        r'text-tracks=(["\'])(?P<data>\[.+?\])\1', view_html,
+                        'text tracks', default='{}', group='data'), video_id,
+                    transform_source=lambda s: js_to_json(unescapeHTML(s)),
+                    fatal=False)
+                extract_subtitles(text_tracks)
 
         self._sort_formats(formats, field_preference=('height', 'width', 'tbr', 'format_id'))