Create packet.reset() and add P0 TODO

Author: NicolasHug

src/torchcodec/_core/BetaCudaDeviceInterface.cpp

@@ -312,8 +312,10 @@ void BetaCudaDeviceInterface::applyBSF(ReferenceAVPacket& packet) {
   // fields of the filtered packet into the original packet. The filtered packet
   // fields are re-set by av_packet_move_ref, so when it goes out of scope and
   // gets destructed, it's not going to affect the original packet.
-  av_packet_unref(packet.get());
-  av_packet_move_ref(packet.get(), filteredPacket.get());
+  packet.reset(filteredPacket);
+  // TODONVDEC P0: consider cleaner ways to do this. Maybe we should let
+  // applyBSF return a new packet, and maybe that new packet needs to be a field
+  // on the interface to avoid complex lifetime issues.
 }
 
 // Parser triggers this callback within cuvidParseVideoData when a frame is

src/torchcodec/_core/FFMPEGCommon.cpp

@@ -33,6 +33,13 @@ AVPacket* ReferenceAVPacket::operator->() {
   return avPacket_;
 }
 
+void ReferenceAVPacket::reset(ReferenceAVPacket& other) {
+  if (this != &other) {
+    av_packet_unref(avPacket_);
+    av_packet_move_ref(avPacket_, other.avPacket_);
+  }
+}
+
 AVCodecOnlyUseForCallingAVFindBestStream
 makeAVCodecOnlyUseForCallingAVFindBestStream(const AVCodec* codec) {
 #if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(59, 18, 100)

src/torchcodec/_core/FFMPEGCommon.h

@@ -135,6 +135,7 @@ class ReferenceAVPacket {
   ~ReferenceAVPacket();
   AVPacket* get();
   AVPacket* operator->();
+  void reset(ReferenceAVPacket& other);
 };
 
 // av_find_best_stream is not const-correct before commit: