Enable download_track for existing courses if self.track.

common/lib/xmodule/xmodule/video_module.py

@@ -351,6 +351,13 @@ class VideoDescriptor(VideoFields, TabsEditingDescriptor, EmptyDataRawDescriptor
                 if not download_video['explicitly_set']:
                     self.download_video = True
 
+        # for backward compatibility.
+        # If course was existed and was not re-imported by the moment of adding `download_track` field,
+        # we should enable `download_track` if following is true:
+        download_track = editable_fields['download_track']
+        if not download_track['explicitly_set'] and self.track:
+            self.download_track = True
+
     @property
     def editable_metadata_fields(self):
         editable_fields = super(VideoDescriptor, self).editable_metadata_fields

lms/djangoapps/courseware/tests/test_video_mongo.py

@@ -420,13 +420,23 @@ class TestVideoDescriptorInitialization(BaseTestXmodule):
                 'display_name': 'Download Transcript',
                 'help': 'The external URL to download the timed transcript track.',
                 'type': 'Generic',
-                'value': u'',
+                'value': u'http://some_track.srt',
                 'field_name': 'track',
                 'options': [],
             },
+            'download_track': {
+                'default_value': False,
+                'explicitly_set': False,
+                'display_name': 'Transcript Download Allowed',
+                'help': 'Show a link beneath the video to allow students to download the transcript. Note: You must add a link to the HTML5 Transcript field above.',
+                'type': 'Generic',
+                'value': False,
+                'field_name': 'download_track',
+                'options': [],
+            }
         }
         metadata = {
-            'track': None,
+            'track': u'http://some_track.srt',
             'source': 'http://example.org/video.mp4',
             'html5_sources': ['http://youtu.be/OEoXaMPEzfM.mp4'],
         }
@@ -437,6 +447,7 @@ class TestVideoDescriptorInitialization(BaseTestXmodule):
         self.assertIn('source', fields)
         self.assertFalse(self.item_module.download_video)
         self.assertTrue(self.item_module.source_visible)
+        self.assertTrue(self.item_module.download_track)
 
     def test_source_is_empty(self):
         metadata = {