VideoClips windows fixes (#1661)

* remove windows skips from video_utils tests, now that they pass

* replace lambda in videoclips in order to be pickled on windows and update tests

test/test_datasets_video_utils.py

@@ -59,10 +59,9 @@ class Tester(unittest.TestCase):
         self.assertTrue(r.equal(expected))
 
     @unittest.skipIf(not io.video._av_available(), "this test requires av")
-    @unittest.skipIf(sys.platform == 'win32', 'temporarily disabled on Windows')
     def test_video_clips(self):
         with get_list_of_videos(num_videos=3) as video_list:
-            video_clips = VideoClips(video_list, 5, 5)
+            video_clips = VideoClips(video_list, 5, 5, num_workers=2)
             self.assertEqual(video_clips.num_clips(), 1 + 2 + 3)
             for i, (v_idx, c_idx) in enumerate([(0, 0), (1, 0), (1, 1), (2, 0), (2, 1), (2, 2)]):
                 video_idx, clip_idx = video_clips.get_clip_location(i)
@@ -84,12 +83,11 @@ class Tester(unittest.TestCase):
                 self.assertEqual(clip_idx, c_idx)
 
     @unittest.skipIf(not io.video._av_available(), "this test requires av")
-    @unittest.skipIf(sys.platform == 'win32', 'temporarily disabled on Windows')
     def test_video_clips_custom_fps(self):
         with get_list_of_videos(num_videos=3, sizes=[12, 12, 12], fps=[3, 4, 6]) as video_list:
             num_frames = 4
             for fps in [1, 3, 4, 10]:
-                video_clips = VideoClips(video_list, num_frames, num_frames, fps)
+                video_clips = VideoClips(video_list, num_frames, num_frames, fps, num_workers=2)
                 for i in range(video_clips.num_clips()):
                     video, audio, info, video_idx = video_clips.get_clip(i)
                     self.assertEqual(video.shape[0], num_frames)

torchvision/datasets/video_utils.py

@@ -104,6 +104,9 @@ class VideoClips(object):
             self._init_from_metadata(_precomputed_metadata)
         self.compute_clips(clip_length_in_frames, frames_between_clips, frame_rate)
 
+    def _collate_fn(self, x):
+        return x
+
     def _compute_frame_pts(self):
         self.video_pts = []
         self.video_fps = []
@@ -115,7 +118,7 @@ class VideoClips(object):
             _DummyDataset(self.video_paths),
             batch_size=16,
             num_workers=self.num_workers,
-            collate_fn=lambda x: x)
+            collate_fn=self._collate_fn)
 
         with tqdm(total=len(dl)) as pbar:
             for batch in dl: