如何避免 ffmpeg filter_complex 覆盖文件的 fps？

Question

I'm fairly new to ffmpeg so apologies if this is a simple problem.

I'm trying to tile four 60fps videos using the script below. It works, but the output is at 25fps. When I try to use -r to force it back to 60, it looks like 25fps upsampled to 60, counting duplicated frames when rendering.

How can I preserve the original files?

ffmpeg -i vln1.mp4 -i vln2.mp4 -i vla.mp4 -i cello.mp4 -filter_complex "nullsrc=size=2800x2400 [base]; [0:v] setpts=PTS-STARTPTS, scale=2800x600 [A]; [1:v] setpts=PTS-STARTPTS, scale=2800x600 [B]; [2:v] setpts=PTS-STARTPTS, scale=2800x600 [C]; [3:v] setpts=PTS-STARTPTS, scale=2800x600 [D]; [base] [A] overlay=shortest=0 [tmp1]; [tmp1][B] overlay=shortest=0:y=600 [tmp2]; [tmp2][C] overlay=shortest=0:y=1200 [tmp3]; [tmp3][D] overlay=shortest=0:y=1800" -c:v libx264 quartetscore.mp4

Answer 1

Set the frame rate for the nullsrc filter (default is 25 fps):

ffmpeg -i vln1.mp4 -i vln2.mp4 -i vla.mp4 -i cello.mp4 -filter_complex "nullsrc=size=2800x2400:rate=60 [base]; [0:v] setpts=PTS-STARTPTS, scale=2800x600 [A]; [1:v] setpts=PTS-STARTPTS, scale=2800x600 [B]; [2:v] setpts=PTS-STARTPTS, scale=2800x600 [C]; [3:v] setpts=PTS-STARTPTS, scale=2800x600 [D]; [base] [A] overlay=shortest=0 [tmp1]; [tmp1][B] overlay=shortest=0:y=600 [tmp2]; [tmp2][C] overlay=shortest=0:y=1200 [tmp3]; [tmp3][D] overlay=shortest=0:y=1800" -c:v libx264 quartetscore.mp4

Or if you want to stack just use the hstack filter instead of nullsrc and multiple overlay:

ffmpeg -i vln1.mp4 -i vln2.mp4 -i vla.mp4 -i cello.mp4 -filter_complex "[0:v] setpts=PTS-STARTPTS, scale=2800x600 [A]; [1:v] setpts=PTS-STARTPTS, scale=2800x600 [B]; [2:v] setpts=PTS-STARTPTS, scale=2800x600 [C]; [3:v] setpts=PTS-STARTPTS, scale=2800x600 [D];[A][B][C][D]hstack=inputs=4" -c:v libx264 quartetscore.mp4

See Vertically or horizontally stack (mosaic) several videos using ffmpeg? for many more examples.