ui/nvenc: Override lag in frames to use Max. B-Frames

source/ui/nvenc_h264_handler.cpp

@@ -85,6 +85,12 @@ void obsffmpeg::ui::nvenc_h264_handler::override_visible_name(const AVCodec*, st
 	name = "H.264/AVC Encoder (NVidia NVENC)";
 }
 
+void obsffmpeg::ui::nvenc_h264_handler::override_lag_in_frames(size_t& lag, obs_data_t* settings, const AVCodec* codec,
+                                                               AVCodecContext* context)
+{
+	nvenc::override_lag_in_frames(lag, settings, codec, context);
+}
+
 void obsffmpeg::ui::nvenc_h264_handler::get_defaults(obs_data_t* settings, const AVCodec* codec,
                                                      AVCodecContext* context)
 {

source/ui/nvenc_h264_handler.hpp

@@ -36,6 +36,9 @@ namespace obsffmpeg {
 			public:
 			virtual void override_visible_name(const AVCodec* codec, std::string& name) override;
 
+			virtual void override_lag_in_frames(size_t& lag, obs_data_t* settings, const AVCodec* codec,
+			                                    AVCodecContext* context) override;
+
 			virtual void get_defaults(obs_data_t* settings, const AVCodec* codec,
 			                          AVCodecContext* context) override;
 

source/ui/nvenc_hevc_handler.cpp

@@ -87,6 +87,12 @@ void obsffmpeg::ui::nvenc_hevc_handler::override_visible_name(const AVCodec*, st
 	name = "H.265/HEVC Encoder (NVidia NVENC)";
 }
 
+void obsffmpeg::ui::nvenc_hevc_handler::override_lag_in_frames(size_t& lag, obs_data_t* settings, const AVCodec* codec,
+                                                               AVCodecContext* context)
+{
+	nvenc::override_lag_in_frames(lag, settings, codec, context);
+}
+
 void obsffmpeg::ui::nvenc_hevc_handler::get_defaults(obs_data_t* settings, const AVCodec* codec,
                                                      AVCodecContext* context)
 {

source/ui/nvenc_hevc_handler.hpp

@@ -36,6 +36,9 @@ namespace obsffmpeg {
 			public:
 			virtual void override_visible_name(const AVCodec* codec, std::string& name) override;
 
+			virtual void override_lag_in_frames(size_t& lag, obs_data_t* settings, const AVCodec* codec,
+			                                    AVCodecContext* context) override;
+
 			virtual void get_defaults(obs_data_t* settings, const AVCodec* codec,
 			                          AVCodecContext* context) override;
 

source/ui/nvenc_shared.cpp

@@ -131,6 +131,17 @@ std::map<b_ref_mode, std::string> obsffmpeg::nvenc::b_ref_mode_to_opt{
     {b_ref_mode::MIDDLE, "middle"},
 };
 
+void obsffmpeg::nvenc::override_lag_in_frames(size_t& lag, obs_data_t* settings, const AVCodec* codec,
+                                              AVCodecContext* context)
+{
+	// With NVENC, the number of frames lagged before we get our first
+	// packet is determined by the number of b-frames. Threads, lookahead
+	// frames and various other settings are ignored.
+	// The minimum number of lagged frames is 1.
+
+	lag = 1ull + static_cast<size_t>(context->max_b_frames);
+}
+
 void obsffmpeg::nvenc::get_defaults(obs_data_t* settings, const AVCodec*, AVCodecContext*)
 {
 	obs_data_set_default_int(settings, ST_PRESET, static_cast<int64_t>(preset::DEFAULT));

source/ui/nvenc_shared.hpp

@@ -75,6 +75,9 @@ namespace obsffmpeg {
 
 		extern std::map<b_ref_mode, std::string> b_ref_mode_to_opt;
 
+		void override_lag_in_frames(size_t& lag, obs_data_t* settings, const AVCodec* codec,
+		                            AVCodecContext* context);
+
 		void get_defaults(obs_data_t* settings, const AVCodec* codec, AVCodecContext* context);
 
 		void get_properties_pre(obs_properties_t* props, const AVCodec* codec);