Multitrack Video Does Not Transcode Real Time
Solution 1:
The missing piece to the puzzle was -rc-lookahead which was omitted from the second command on my original post somehow.
If I add -rc-lookahead 60 to the multitrack file it fairly quickly gets up to realtime transcoding, example:
ffmpeg -y -hide_banner -thread_queue_size 9999 -indexmem 9999 -f dshow -rtbufsize 2147M -video_size 3840x2160 `
-framerate 60 -pixel_format nv12 -i video="Video (Pro Capture)":audio="ADAT (3+4) (RME Fireface UC)" `
-thread_queue_size 9999 -indexmem 9999 -f dshow -rtbufsize 2147M -video_size 3840x2160 -framerate 60 -pixel_format nv12 `
-i video="AVerMedia HD Capture GC573 1":audio="Analog (1+2) (RME Fireface UC)" `
-thread_queue_size 9999 -indexmem 9999 -f dshow -rtbufsize 2147M -video_size 1920x1080 -framerate 60 -pixel_format yuv420p `
-i video="Game Capture HD60 Pro (Video) (#01)":audio="Game Capture HD60 Pro (Audio) (#01)" `
-thread_queue_size 9999 -indexmem 9999 -f dshow -rtbufsize 2147M -i audio="ADAT (5+6) (RME Fireface UC)" `
-thread_queue_size 9999 -indexmem 9999 -f dshow -rtbufsize 2147M -i audio="SPDIF/ADAT (1+2) (RME Fireface UC)" `
-c:v h264_nvenc -preset: llhp -pix_fmt nv12 -rc-lookahead 60 -b:v 288M -minrate 288M -maxrate 288M -bufsize 288M -c:a aac `
-ar 44100 -b:a 384k -vsync 1 -max_muxing_queue_size 9999 -map 0 -map 1 -map 2 -map 3 -map 4 `
-f segment -segment_time 600 -segment_wrap 9 -reset_timestamps 1 -segment_format_options max_delay=0 `
C:\Users\djcim\Videos\FFmpeg\FFmpeg%02d.ts