[lynda:course] Add webpage extraction fallback (closes #12238)

youtube_dl/extractor/lynda.py

@@ -260,9 +260,24 @@ class LyndaCourseIE(LyndaBaseIE):
         course_path = mobj.group('coursepath')
         course_id = mobj.group('courseid')
 
+        item_template = 'https://www.lynda.com/%s/%%s-4.html' % course_path
+
         course = self._download_json(
             'https://www.lynda.com/ajax/player?courseId=%s&type=course' % course_id,
-            course_id, 'Downloading course JSON')
+            course_id, 'Downloading course JSON', fatal=False)
+
+        if not course:
+            webpage = self._download_webpage(url, course_id)
+            entries = [
+                self.url_result(
+                    item_template % video_id, ie=LyndaIE.ie_key(),
+                    video_id=video_id)
+                for video_id in re.findall(
+                    r'data-video-id=["\'](\d+)', webpage)]
+            return self.playlist_result(
+                entries, course_id,
+                self._og_search_title(webpage, fatal=False),
+                self._og_search_description(webpage))
 
         if course.get('Status') == 'NotFound':
             raise ExtractorError(
@@ -283,7 +298,7 @@ class LyndaCourseIE(LyndaBaseIE):
                 if video_id:
                     entries.append({
                         '_type': 'url_transparent',
-                        'url': 'https://www.lynda.com/%s/%s-4.html' % (course_path, video_id),
+                        'url': item_template % video_id,
                         'ie_key': LyndaIE.ie_key(),
                         'chapter': chapter.get('Title'),
                         'chapter_number': int_or_none(chapter.get('ChapterIndex')),