Better handle corrupted videos (#1463)

* Handle corrupted video headers in io

* Catch exceptions while decoding partly-corrupted files

* Add more tests

test/test_io.py

@@ -236,6 +236,41 @@ class Tester(unittest.TestCase):
             self.assertEqual(len(lv), 4)
             self.assertTrue(data[4:8].equal(lv))
 
+    def test_read_video_corrupted_file(self):
+        with tempfile.NamedTemporaryFile(suffix='.mp4') as f:
+            f.write(b'This is not an mpg4 file')
+            video, audio, info = io.read_video(f.name)
+            self.assertIsInstance(video, torch.Tensor)
+            self.assertIsInstance(audio, torch.Tensor)
+            self.assertEqual(video.numel(), 0)
+            self.assertEqual(audio.numel(), 0)
+            self.assertEqual(info, {})
+
+    def test_read_video_timestamps_corrupted_file(self):
+        with tempfile.NamedTemporaryFile(suffix='.mp4') as f:
+            f.write(b'This is not an mpg4 file')
+            video_pts, video_fps = io.read_video_timestamps(f.name)
+            self.assertEqual(video_pts, [])
+            self.assertIs(video_fps, None)
+
+    def test_read_video_partially_corrupted_file(self):
+        with temp_video(5, 4, 4, 5, lossless=True) as (f_name, data):
+            with open(f_name, 'r+b') as f:
+                size = os.path.getsize(f_name)
+                bytes_to_overwrite = size // 10
+                # seek to the middle of the file
+                f.seek(5 * bytes_to_overwrite)
+                # corrupt 10% of the file from the middle
+                f.write(b'\xff' * bytes_to_overwrite)
+            # this exercises the container.decode assertion check
+            video, audio, info = io.read_video(f.name, pts_unit='sec')
+            # check that size is not equal to 5, but 3
+            self.assertEqual(len(video), 3)
+            # but the valid decoded content is still correct
+            self.assertTrue(video[:3].equal(data[:3]))
+            # and the last few frames are wrong
+            self.assertFalse(video.equal(data))
+
     # TODO add tests for audio
 
 

torchvision/io/video.py

@@ -124,13 +124,17 @@ def _read_from_stream(container, start_offset, end_offset, pts_unit, stream, str
         # print("Corrupted file?", container.name)
         return []
     buffer_count = 0
-    for idx, frame in enumerate(container.decode(**stream_name)):
-        frames[frame.pts] = frame
-        if frame.pts >= end_offset:
-            if should_buffer and buffer_count < max_buffer_size:
-                buffer_count += 1
-                continue
-            break
+    try:
+        for idx, frame in enumerate(container.decode(**stream_name)):
+            frames[frame.pts] = frame
+            if frame.pts >= end_offset:
+                if should_buffer and buffer_count < max_buffer_size:
+                    buffer_count += 1
+                    continue
+                break
+    except av.AVError:
+        # TODO add a warning
+        pass
     # ensure that the results are sorted wrt the pts
     result = [frames[i] for i in sorted(frames) if start_offset <= frames[i].pts <= end_offset]
     if start_offset > 0 and start_offset not in frames:
@@ -193,25 +197,39 @@ def read_video(filename, start_pts=0, end_pts=None, pts_unit='pts'):
         raise ValueError("end_pts should be larger than start_pts, got "
                          "start_pts={} and end_pts={}".format(start_pts, end_pts))
 
-    container = av.open(filename, metadata_errors='ignore')
     info = {}
-
     video_frames = []
-    if container.streams.video:
-        video_frames = _read_from_stream(container, start_pts, end_pts, pts_unit,
-                                         container.streams.video[0], {'video': 0})
-        info["video_fps"] = float(container.streams.video[0].average_rate)
     audio_frames = []
-    if container.streams.audio:
-        audio_frames = _read_from_stream(container, start_pts, end_pts, pts_unit,
-                                         container.streams.audio[0], {'audio': 0})
-        info["audio_fps"] = container.streams.audio[0].rate
 
-    container.close()
+    try:
+        container = av.open(filename, metadata_errors='ignore')
+    except av.AVError:
+        # TODO raise a warning?
+        pass
+    else:
+        if container.streams.video:
+            video_frames = _read_from_stream(container, start_pts, end_pts, pts_unit,
+                                             container.streams.video[0], {'video': 0})
+            video_fps = container.streams.video[0].average_rate
+            # guard against potentially corrupted files
+            if video_fps is not None:
+                info["video_fps"] = float(video_fps)
+
+        if container.streams.audio:
+            audio_frames = _read_from_stream(container, start_pts, end_pts, pts_unit,
+                                             container.streams.audio[0], {'audio': 0})
+            info["audio_fps"] = container.streams.audio[0].rate
+
+        container.close()
 
     vframes = [frame.to_rgb().to_ndarray() for frame in video_frames]
     aframes = [frame.to_ndarray() for frame in audio_frames]
-    vframes = torch.as_tensor(np.stack(vframes))
+
+    if vframes:
+        vframes = torch.as_tensor(np.stack(vframes))
+    else:
+        vframes = torch.empty((0, 1, 1, 3), dtype=torch.uint8)
+
     if aframes:
         aframes = np.concatenate(aframes, 1)
         aframes = torch.as_tensor(aframes)
@@ -255,21 +273,30 @@ def read_video_timestamps(filename, pts_unit='pts'):
     """
     _check_av_available()
 
-    container = av.open(filename, metadata_errors='ignore')
-
     video_frames = []
     video_fps = None
-    if container.streams.video:
-        video_stream = container.streams.video[0]
-        video_time_base = video_stream.time_base
-        if _can_read_timestamps_from_packets(container):
-            # fast path
-            video_frames = [x for x in container.demux(video=0) if x.pts is not None]
-        else:
-            video_frames = _read_from_stream(container, 0, float("inf"), pts_unit,
-                                             video_stream, {'video': 0})
-        video_fps = float(video_stream.average_rate)
-    container.close()
+
+    try:
+        container = av.open(filename, metadata_errors='ignore')
+    except av.AVError:
+        # TODO add a warning
+        pass
+    else:
+        if container.streams.video:
+            video_stream = container.streams.video[0]
+            video_time_base = video_stream.time_base
+            if _can_read_timestamps_from_packets(container):
+                # fast path
+                video_frames = [x for x in container.demux(video=0) if x.pts is not None]
+            else:
+                video_frames = _read_from_stream(container, 0, float("inf"), pts_unit,
+                                                 video_stream, {'video': 0})
+            video_fps = float(video_stream.average_rate)
+        container.close()
+
+    pts = [x.pts for x in video_frames]
+
     if pts_unit == 'sec':
-        return [x.pts * video_time_base for x in video_frames], video_fps
-    return [x.pts for x in video_frames], video_fps
+        pts = [x * video_time_base for x in pts]
+
+    return pts, video_fps