fix(security): classify DeepStream as GPU backend and enforce pixel limits (#50755)

Signed-off-by: jperezde <jperezde@redhat.com>

tests/multimodal/media/test_video.py

@@ -470,3 +470,31 @@ class TestMergeKwargsGpuBackendPolicy:
         )
         assert result.get("backend") != "pynvvideocodec"
         assert result["video_backend"] == "pynvvideocodec"
+
+    def test_deepstream_requires_gpu(self):
+        assert VIDEO_LOADER_REGISTRY.backend_requires_gpu("deepstream")
+
+    def test_strips_backend_deepstream_when_not_static(self):
+        result = VideoMediaIO.merge_kwargs(
+            default_kwargs=None,
+            runtime_kwargs={"backend": "deepstream"},
+        )
+        assert result.get("backend") != "deepstream"
+
+    def test_preserves_backend_deepstream_when_static(self):
+        result = VideoMediaIO.merge_kwargs(
+            default_kwargs={"backend": "deepstream"},
+            runtime_kwargs={"backend": "deepstream", "num_frames": 8},
+        )
+        assert result["backend"] == "deepstream"
+        assert result["num_frames"] == 8
+
+    def test_strips_pool_size_from_runtime(self):
+        result = VideoMediaIO.merge_kwargs(
+            default_kwargs={"backend": "deepstream"},
+            runtime_kwargs={"backend": "deepstream", "pool_size": 4},
+        )
+        assert "pool_size" not in result
+
+    def test_unknown_backend_not_treated_as_gpu(self):
+        assert not VIDEO_LOADER_REGISTRY.backend_requires_gpu("totally_unknown")