Added check for invalid input file (#3932)

test/test_video_reader.py

 import collections
 import math
 import os
-import time
 import unittest
 from fractions import Fraction
 
@@ -9,6 +8,7 @@ import numpy as np
 import torch
 import torchvision.io as io
 from numpy.random import randint
+from torchvision import set_video_backend
 from torchvision.io import _HAS_VIDEO_OPT
 from common_utils import PY39_SKIP
 from _assert_utils import assert_equal
@@ -23,9 +23,6 @@ except ImportError:
     av = None
 
 
-from urllib.error import URLError
-
-
 VIDEO_DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)), "assets", "videos")
 
 CheckerConfig = [
@@ -1277,6 +1274,15 @@ class TestVideoReader(unittest.TestCase):
                     self.assertGreaterEqual(
                         torch.mean(torch.isclose(audio.float(), arr).float()), 0.99)
 
+    def test_invalid_file(self):
+        set_video_backend('video_reader')
+        with self.assertRaises(RuntimeError):
+            io.read_video('foo.mp4')
+
+        set_video_backend('pyav')
+        with self.assertRaises(RuntimeError):
+            io.read_video('foo.mp4')
+
 
 if __name__ == "__main__":
     unittest.main()

torchvision/io/video.py

 import gc
 import math
+import os
 import re
 import warnings
 from typing import Any, Dict, List, Optional, Tuple, Union
@@ -258,6 +259,9 @@ def read_video(
 
     from torchvision import get_video_backend
 
+    if not os.path.exists(filename):
+        raise RuntimeError(f'File not found: {filename}')
+
     if get_video_backend() != "pyav":
         return _video_opt._read_video(filename, start_pts, end_pts, pts_unit)