[FFmpeg-user] Max rtbufsize Via dshow

[Gabriel Balaich]

Up until a few days ago I had been running two capture cards, 1x4K card and
1x1080P card, I would encode both streams with a
GTX 1080 no dropped frames no issues. But just recently I replaced the
1080P capture card with another 4K capture card to prep
for a new camera and can't get things working gracefully. On my first test
encoding 2x4K60 streams simultaneously I dropped
frames starting the recording *and *ending the recording, but nothing
in-between.

Errors displayed:
[dshow @ 000001499bb17180] real-time buffer [Video (00 Pro Capture HDMI
4K+)] [video input] too full or near too full (62% of
size: 2147480000 [rtbufsize parameter])! frame dropped!
[dshow @ 00000149944e7080] real-time buffer [AVerMedia HD Capture GC573 1]
[video input] too full or near too full (62% of
size: 2147480000 [rtbufsize parameter])! frame dropped!

The obvious answer, according to the warning, would be increasing rtbufsize
but I seem to have hit the cap... If I try to increase
rtbufsize passed 2147.48M I get another error:
[dshow @ 00000250df6c7080] Value 3000000000.000000 for parameter
'rtbufsize' out of range [0 - 2.14748e+09]
[dshow @ 00000250df6c7080] Error setting option rtbufsize to value 3000M.
video=AVerMedia HD Capture GC573 1:audio=SPDIF/ADAT (1+2) (RME Fireface
UC): Result too large

Is this a baked in limitation of FFmpeg or dshow? And if it is, why impose
said limitation?

Since then I've tried messing with other parts of my command and found that
by re-arranging my inputs / outputs I can prevent
frame drops upon starting a recording but I still can't end a recording
without dropping a bunch of frames.

Anyone know why re-arranging my inputs / outputs would prevent frames from
dropping when starting a recording or affect
anything? Is it possible to bypass the rtbufsize cap? Any other ideas?

Here is my full command, Ignore the blank numbers next to -ss, will be used
to sync outputs when everything is working:
ffmpeg -y -hide_banner -thread_queue_size 9999 -indexmem 9999
-guess_layout_max 0 -f dshow -rtbufsize 2147.48M `
-i audio="Analog (1+2) (RME Fireface UC)" `
-thread_queue_size 9999 -indexmem 9999 -guess_layout_max 0 -f dshow
-rtbufsize 2147.48M `
-i audio="ADAT (5+6) (RME Fireface UC)" `
-thread_queue_size 9999 -indexmem 9999 -r 25 -f lavfi -rtbufsize 2147.48M
-i color=c=black:s=50x50 `
-thread_queue_size 9999 -indexmem 9999 -guess_layout_max 0 -f dshow
-video_size 3840x2160 -rtbufsize 2147.48M `
-framerate 60 -pixel_format nv12 -i video="AVerMedia HD Capture GC573
1":audio="SPDIF/ADAT (1+2) (RME Fireface UC)" `
-thread_queue_size 9999 -indexmem 9999 -guess_layout_max 0 -f dshow
-video_size 3840x2160 -rtbufsize 2147.48M `
-framerate 60 -pixel_format nv12 -i video="Video (00 Pro Capture HDMI
4K+)":audio="ADAT (3+4) (RME Fireface UC)" `
-map 2,0 -map 0 -c:v libx264 -r 25 -rc-lookahead 50 -forced-idr 1
-sc_threshold 0 -flags +cgop `
-force_key_frames "expr:gte(t,n_forced*2)" -preset ultrafast -pix_fmt nv12
-b:v 16K -minrate 16K -maxrate 16K -bufsize 16k `
-c:a aac -ar 44100 -b:a 384k -ac 2 -af "aresample=async=250" -vsync 1 -ss
00:00:00.000 `
-max_muxing_queue_size 9999 -f segment -segment_time 600 -segment_wrap 9
-reset_timestamps 1 `
-segment_format_options max_delay=0
C:\Users\djcim\Videos\Main\Discord\Discord%02d.ts `
-map 2,1 -map 1 -c:v libx264 -r 25 -rc-lookahead 50 -forced-idr 1
-sc_threshold 0 -flags +cgop `
-force_key_frames "expr:gte(t,n_forced*2)" -preset ultrafast -pix_fmt nv12
-b:v 16K -minrate 16K -maxrate 16K -bufsize 16k `
-c:a aac -ar 44100 -b:a 384k -ac 2 -af "aresample=async=250" -vsync 1 -ss
00:00:00.000 `
-max_muxing_queue_size 9999 -f segment -segment_time 600 -segment_wrap 9
-reset_timestamps 1 `
-segment_format_options max_delay=0
C:\Users\djcim\Videos\Main\Soundboard\Soundboard%02d.ts `
-map 3:0,3:1 -map 3:1 -c:v h264_nvenc -r 60 -rc-lookahead 120 -forced-idr 1
-strict_gop 1 -sc_threshold 0 -flags +cgop `
-force_key_frames "expr:gte(t,n_forced*2)" -preset: llhp -pix_fmt nv12 -b:v
250M -minrate 250M -maxrate 250M -bufsize 250M `
-c:a aac -ar 44100 -b:a 384k -ac 2 -af "pan=mono|c0=c0,
aresample=async=250" -vsync 1 -ss 00:00:00.000 `
-max_muxing_queue_size 9999 -f segment -segment_time 600 -segment_wrap 9
-reset_timestamps 1 `
-segment_format_options max_delay=0
C:\Users\djcim\Videos\Main\Camera\Camera%02d.ts `
-map 4:0,4:1 -map 4:1 -c:v h264_nvenc -r 60 -rc-lookahead 120 -forced-idr 1
-strict_gop 1 -sc_threshold 0 -flags +cgop `
-force_key_frames "expr:gte(t,n_forced*2)" -preset: llhp -pix_fmt nv12 -b:v
250M -minrate 250M -maxrate 250M -bufsize 250M `
-c:a aac -ar 44100 -b:a 384k -ac 2 -af "atrim=0.086, asetpts=PTS-STARTPTS,
aresample=async=250" -vsync 1 -ss 00:00:00.000 `
-max_muxing_queue_size 9999 -f segment -segment_time 600 -segment_wrap 9
-reset_timestamps 1 `
-segment_format_options max_delay=0
C:\Users\djcim\Videos\Main\Magewell\Magewell%02d.ts