switch _.code._get_backend_details() to new api

Author: Molly Xu

src/torchcodec/decoders/_video_decoder.py

@@ -41,6 +41,7 @@ def __init__(self):
         self.status_known = False
         self._nvcuvid_unavailable = False
         self._video_not_supported = False
+        self._backend = ""
 
     def __bool__(self):
         """Returns True if fallback occurred."""
@@ -60,8 +61,11 @@ def __str__(self):
             reasons.append("Video not supported")
 
         if reasons:
-            return "Fallback status: Falling back due to: " + ", ".join(reasons)
-        return "Fallback status: No fallback required"
+            return (
+                f"[{self._backend}] Fallback status: Falling back due to: "
+                + ", ".join(reasons)
+            )
+        return f"[{self._backend}] Fallback status: No fallback required"
 
 
 class VideoDecoder:
@@ -241,6 +245,11 @@ def cpu_fallback(self) -> CpuFallbackStatus:
             if "status unknown" not in backend_details:
                 self._cpu_fallback.status_known = True
 
+                for backend in ("FFmpeg CUDA", "Beta CUDA", "CPU"):
+                    if backend_details.startswith(backend):
+                        self._cpu_fallback._backend = backend
+                        break
+
                 if "CPU fallback" in backend_details:
                     if "NVCUVID not available" in backend_details:
                         self._cpu_fallback._nvcuvid_unavailable = True

test/test_decoders.py

@@ -1672,22 +1672,27 @@ def test_beta_cuda_interface_cpu_fallback(self):
         # to the CPU path, too.
 
         ref_dec = VideoDecoder(H265_VIDEO.path, device="cuda")
-        ref_frames = ref_dec.get_frame_at(0)
-        assert (
-            _core._get_backend_details(ref_dec._decoder)
-            == "FFmpeg CUDA Device Interface. Using CPU fallback."
-        )
+
+        # Before accessing any frames, status should be unknown
+        assert not ref_dec.cpu_fallback.status_known
+
+        ref_frame = ref_dec.get_frame_at(0)
+
+        assert "FFmpeg CUDA" in str(ref_dec.cpu_fallback)
+        assert ref_dec.cpu_fallback.status_known
+        assert bool(ref_dec.cpu_fallback)
 
         with set_cuda_backend("beta"):
             beta_dec = VideoDecoder(H265_VIDEO.path, device="cuda")
 
-        assert (
-            _core._get_backend_details(beta_dec._decoder)
-            == "Beta CUDA Device Interface. Using CPU fallback."
-        )
+        assert "Beta CUDA" in str(beta_dec.cpu_fallback)
+        # For beta interface, status is known immediately
+        assert beta_dec.cpu_fallback.status_known
+        assert bool(beta_dec.cpu_fallback)
+
         beta_frame = beta_dec.get_frame_at(0)
 
-        assert psnr(ref_frames.data, beta_frame.data) > 25
+        assert psnr(ref_frame.data, beta_frame.data) > 25
 
     @needs_cuda
     def test_beta_cuda_interface_error(self):
@@ -1715,7 +1720,8 @@ def test_set_cuda_backend(self):
         # Check that the default is the ffmpeg backend
         assert _get_cuda_backend() == "ffmpeg"
         dec = VideoDecoder(H265_VIDEO.path, device="cuda")
-        assert _core._get_backend_details(dec._decoder).startswith("FFmpeg CUDA")
+        _ = dec.get_frame_at(0)
+        assert "FFmpeg CUDA" in str(dec.cpu_fallback)
 
         # Check the setting "beta" effectively uses the BETA backend.
         # We also show that the affects decoder creation only. When the decoder
@@ -1724,9 +1730,9 @@ def test_set_cuda_backend(self):
         with set_cuda_backend("beta"):
             dec = VideoDecoder(H265_VIDEO.path, device="cuda")
         assert _get_cuda_backend() == "ffmpeg"
-        assert _core._get_backend_details(dec._decoder).startswith("Beta CUDA")
+        assert "Beta CUDA" in str(dec.cpu_fallback)
         with set_cuda_backend("ffmpeg"):
-            assert _core._get_backend_details(dec._decoder).startswith("Beta CUDA")
+            assert "Beta CUDA" in str(dec.cpu_fallback)
 
         # Hacky way to ensure passing "cuda:1" is supported by both backends. We
         # just check that there's an error when passing cuda:N where N is too
@@ -1762,23 +1768,6 @@ def test_cpu_fallback_h265_video_ffmpeg_cuda(self):
         assert bool(decoder.cpu_fallback)
         assert "Fallback status: Falling back due to:" in str(decoder.cpu_fallback)
 
-    @needs_cuda
-    def test_cpu_fallback_h265_video_beta_cuda(self):
-        """Test that H265 video triggers CPU fallback on Beta CUDA interface."""
-        with set_cuda_backend("beta"):
-            decoder = VideoDecoder(H265_VIDEO.path, device="cuda")
-
-        # Before accessing any frames, status should be unknown
-        assert decoder.cpu_fallback.status_known
-
-        _ = decoder.get_frame_at(0)
-
-        # After accessing frames, status should be known
-        assert decoder.cpu_fallback.status_known
-
-        assert bool(decoder.cpu_fallback)
-        assert "Fallback status: Falling back due to:" in str(decoder.cpu_fallback)
-
     @needs_cuda
     def test_cpu_fallback_no_fallback_on_supported_video(self):
         """Test that supported videos don't trigger fallback on CUDA."""