Allow cuda device to be passed without the index for GPU decoding (#5505)

Author: prabhat00155

test/test_video_gpu_decoder.py

@@ -30,7 +30,7 @@ class TestVideoGPUDecoder:
     )
     def test_frame_reading(self, video_file):
         full_path = os.path.join(VIDEO_DIR, video_file)
-        decoder = VideoReader(full_path, device="cuda:0")
+        decoder = VideoReader(full_path, device="cuda")
         with av.open(full_path) as container:
             for av_frame in container.decode(container.streams.video[0]):
                 av_frames = torch.tensor(av_frame.to_rgb(src_colorspace="ITU709").to_ndarray())
@@ -54,7 +54,7 @@ def test_frame_reading(self, video_file):
         ],
     )
     def test_seek_reading(self, keyframes, full_path, duration):
-        decoder = VideoReader(full_path, device="cuda:0")
+        decoder = VideoReader(full_path, device="cuda")
         time = duration / 2
         decoder.seek(time, keyframes_only=keyframes)
         with av.open(full_path) as container:
@@ -80,7 +80,7 @@ def test_seek_reading(self, keyframes, full_path, duration):
     )
     def test_metadata(self, video_file):
         full_path = os.path.join(VIDEO_DIR, video_file)
-        decoder = VideoReader(full_path, device="cuda:0")
+        decoder = VideoReader(full_path, device="cuda")
         video_metadata = decoder.get_metadata()["video"]
         with av.open(full_path) as container:
             video = container.streams.video[0]

torchvision/csrc/io/decoder/gpu/gpu_decoder.cpp

@@ -3,9 +3,10 @@
 
 /* Set cuda device, create cuda context and initialise the demuxer and decoder.
  */
-GPUDecoder::GPUDecoder(std::string src_file, int64_t dev)
-    : demuxer(src_file.c_str()), device(dev) {
-  at::cuda::CUDAGuard device_guard(device);
+GPUDecoder::GPUDecoder(std::string src_file, torch::Device dev)
+    : demuxer(src_file.c_str()) {
+  at::cuda::CUDAGuard device_guard(dev);
+  device = device_guard.current_device().index();
   check_for_cuda_errors(
       cuDevicePrimaryCtxRetain(&ctx, device), __LINE__, __FILE__);
   decoder.init(ctx, ffmpeg_to_codec(demuxer.get_video_codec()));
@@ -58,7 +59,7 @@ c10::Dict<std::string, c10::Dict<std::string, double>> GPUDecoder::
 
 TORCH_LIBRARY(torchvision, m) {
   m.class_<GPUDecoder>("GPUDecoder")
-      .def(torch::init<std::string, int64_t>())
+      .def(torch::init<std::string, torch::Device>())
       .def("seek", &GPUDecoder::seek)
       .def("get_metadata", &GPUDecoder::get_metadata)
       .def("next", &GPUDecoder::decode);

torchvision/csrc/io/decoder/gpu/gpu_decoder.h

@@ -5,7 +5,7 @@
 
 class GPUDecoder : public torch::CustomClassHolder {
  public:
-  GPUDecoder(std::string, int64_t);
+  GPUDecoder(std::string, torch::Device);
   ~GPUDecoder();
   torch::Tensor decode();
   void seek(double, bool);

torchvision/io/video_reader.py

@@ -84,6 +84,7 @@ class VideoReader:
             will depend on the version of FFMPEG codecs supported.
 
         device (str, optional): Device to be used for decoding. Defaults to ``"cpu"``.
+            To use GPU decoding, pass ``device="cuda"``.
 
     """
 
@@ -95,9 +96,7 @@ def __init__(self, path: str, stream: str = "video", num_threads: int = 0, devic
             if not _HAS_GPU_VIDEO_DECODER:
                 raise RuntimeError("Not compiled with GPU decoder support.")
             self.is_cuda = True
-            if device.index is None:
-                raise RuntimeError("Invalid cuda device!")
-            self._c = torch.classes.torchvision.GPUDecoder(path, device.index)
+            self._c = torch.classes.torchvision.GPUDecoder(path, device)
             return
         if not _has_video_opt():
             raise RuntimeError(