Automatically send video to CPU in io.write_video (#8537)

Co-authored-by: Nicolas Hug <nh.nicolas.hug@gmail.com>

test/test_io.py

@@ -255,10 +255,14 @@ def test_read_video_partially_corrupted_file(self):
                 assert_equal(video, data)
 
     @pytest.mark.skipif(sys.platform == "win32", reason="temporarily disabled on Windows")
-    def test_write_video_with_audio(self, tmpdir):
+    @pytest.mark.parametrize("device", ["cpu", "cuda"])
+    def test_write_video_with_audio(self, device, tmpdir):
         f_name = os.path.join(VIDEO_DIR, "R6llTwEh07w.mp4")
         video_tensor, audio_tensor, info = io.read_video(f_name, pts_unit="sec")
 
+        video_tensor = video_tensor.to(device)
+        audio_tensor = audio_tensor.to(device)
+
         out_f_name = os.path.join(tmpdir, "testing.mp4")
         io.video.write_video(
             out_f_name,

torchvision/io/video.py

@@ -80,7 +80,7 @@ def write_video(
     if not torch.jit.is_scripting() and not torch.jit.is_tracing():
         _log_api_usage_once(write_video)
     _check_av_available()
-    video_array = torch.as_tensor(video_array, dtype=torch.uint8).numpy()
+    video_array = torch.as_tensor(video_array, dtype=torch.uint8).numpy(force=True)
 
     # PyAV does not support floating point numbers with decimal point
     # and will throw OverflowException in case this is not the case