fix

Author: NicolasHug

src/torchcodec/_core/SingleStreamDecoder.h

@@ -311,7 +311,7 @@ class SingleStreamDecoder {
       int streamIndex,
       AVMediaType mediaType,
       const torch::Device& device = torch::kCPU,
-      const std::string_view deviceVariant = "default",
+      const std::string_view deviceVariant = "ffmpeg",
       std::optional<int> ffmpegThreadCount = std::nullopt);
 
   // Returns the "best" stream index for a given media type. The "best" is