Test to ensure transforms are not used with non-CPU

Author: scotts

src/torchcodec/_core/SingleStreamDecoder.cpp

@@ -466,6 +466,10 @@ void SingleStreamDecoder::addVideoStream(
     std::vector<Transform*>& transforms,
     const VideoStreamOptions& videoStreamOptions,
     std::optional<FrameMappings> customFrameMappings) {
+  TORCH_CHECK(
+      transforms.empty() || videoStreamOptions.device == torch::kCPU,
+      "Transforms are only supported for CPU devices.");
+
   addStream(
       streamIndex,
       AVMEDIA_TYPE_VIDEO,

test/test_ops.py

@@ -614,6 +614,15 @@ def test_color_conversion_library_with_scaling(
         assert_frames_equal(filtergraph_frame0, swscale_frame0)
         assert filtergraph_frame0.shape == (3, target_height, target_width)
 
+    @needs_cuda
+    def test_scaling_on_cuda_fails(self):
+        decoder = create_from_file(str(NASA_VIDEO.path))
+        with pytest.raises(
+            RuntimeError,
+            match="Transforms are only supported for CPU devices.",
+        ):
+            add_video_stream(decoder, device="cuda", width=100, height=100)
+
     @pytest.mark.parametrize("dimension_order", ("NHWC", "NCHW"))
     @pytest.mark.parametrize("color_conversion_library", ("filtergraph", "swscale"))
     def test_color_conversion_library_with_dimension_order(