fix auto generated images ffmpeg command

EDUCATOR-2294

video_worker/tests/data/test_instance_config.yaml

@@ -40,3 +40,4 @@ celery_deliver_queue: ""
 global_timeout: 40
 
 instance_prefix: ""
+ffmpeg_compiled: "ffmpeg"

video_worker/tests/test_video_images.py

@@ -39,6 +39,25 @@ class VideoImagesTest(unittest.TestCase):
         with open(TEST_INSTANCE_YAML, 'r') as stream:
             self.settings = yaml.load(stream)
 
+    @patch.object(video_images.VideoImages, 'generate', return_value = ['a/1.png'])
+    @patch.object(video_images.VideoImages, 'upload', return_value = ['s3://images/a/1.png'])
+    @patch.object(video_images.VideoImages, 'update_val')
+    def test_create_and_update(self, mock_update_val, mock_upload, mock_generate):
+        """
+        Verify that VideoImages.create_and_update method works as expected.
+        """
+        video_images.VideoImages(
+            video_object=MockVideo,
+            work_dir=self.work_dir,
+            source_file=self.source_file,
+            jobid=101,
+            settings=self.settings
+        ).create_and_update()
+
+        self.assertTrue(mock_generate.called)
+        mock_upload.assert_called_with(['a/1.png'])
+        mock_update_val.assert_called_with(['s3://images/a/1.png'])
+
     @data(
         {
             'duration': 10, 'positions': [1, 4, 7],
@@ -57,10 +76,6 @@ class VideoImagesTest(unittest.TestCase):
         """
         self.assertEqual(video_images.VideoImages.calculate_positions(duration), positions)
 
-    @unittest.skipIf(
-        'TRAVIS' in os.environ and os.environ['TRAVIS'] == 'true',
-        'Skipping this test on Travis CI due to unavailability of required ffmpeg version.'
-    )
     def test_generate(self):
         """
         Verify that VideoImages.generate method works as expected.

video_worker/video_images.py

@@ -91,10 +91,8 @@ class VideoImages(object):
             generated_images.append(
                 os.path.join(self.work_dir, '{}.png'.format(uuid4().hex))
             )
-            command = ('{ffmpeg} -ss {position} -i {video_file} -vf '
-                       r'select="gt(scene\,0.4)",scale={width}:{height}'
-                       ' -vsync 2 -vframes 1 {output_file}'
-                       ' -hide_banner -y'.format(
+            command = ('{ffmpeg} -ss {position} -i {video_file} -y -vf scale={width}:{height}'
+                       ' -vsync 2 -vframes 1 {output_file}'.format(
                            ffmpeg=self.settings['ffmpeg_compiled'],
                            position=position,
                            video_file=self.source_video_file,