StreamMetadata.sampleAspectRation: use AVRational instead of std::pair

Author: carandraug

src/torchcodec/_core/Metadata.h

@@ -8,12 +8,12 @@
 
 #include <optional>
 #include <string>
-#include <utility>
 #include <vector>
 
 extern "C" {
 #include <libavcodec/avcodec.h>
 #include <libavutil/avutil.h>
+#include <libavutil/rational.h>
 }
 
 namespace facebook::torchcodec {
@@ -46,7 +46,7 @@ struct StreamMetadata {
   // Video-only fields derived from the AVCodecContext.
   std::optional<int64_t> width;
   std::optional<int64_t> height;
-  std::optional<std::pair<int, int>> sampleAspectRatio;
+  std::optional<AVRational> sampleAspectRatio;
 
   // Audio-only fields
   std::optional<int64_t> sampleRate;

src/torchcodec/_core/SingleStreamDecoder.cpp

@@ -459,9 +459,8 @@ void SingleStreamDecoder::addVideoStream(
 
   streamMetadata.width = streamInfo.codecContext->width;
   streamMetadata.height = streamInfo.codecContext->height;
-  streamMetadata.sampleAspectRatio = {
-      streamInfo.codecContext->sample_aspect_ratio.num,
-      streamInfo.codecContext->sample_aspect_ratio.den};
+  streamMetadata.sampleAspectRatio =
+      streamInfo.codecContext->sample_aspect_ratio;
 }
 
 void SingleStreamDecoder::addAudioStream(

src/torchcodec/_core/custom_ops.cpp

@@ -603,9 +603,9 @@ std::string get_stream_json_metadata(
   }
   if (streamMetadata.sampleAspectRatio.has_value()) {
     map["sampleAspectRatioNum"] =
-        std::to_string((*streamMetadata.sampleAspectRatio).first);
+        std::to_string((*streamMetadata.sampleAspectRatio).num);
     map["sampleAspectRatioDen"] =
-        std::to_string((*streamMetadata.sampleAspectRatio).second);
+        std::to_string((*streamMetadata.sampleAspectRatio).den);
   }
   if (streamMetadata.averageFpsFromHeader.has_value()) {
     map["averageFpsFromHeader"] =