[FFmpeg-user] Size of cropped video segments

[Chao Zhou]

Hi team,

I am cropping a video to 9 small segments with the command below:

ffmpeg -i source.mp4 -filter_complex \
"[0:v]crop=1/3*in_w:1/3*in_h:0:0[out1];[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:0[out2];\
[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:0[out3];[0:v]crop=1/3*in_w:1/3*in_h:0:1/3*in_h[out4];\
[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:1/3*in_h[out5];[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:1/3*in_h[out6];\
[0:v]crop=1/3*in_w:1/3*in_h:0:2/3*in_h[out7];[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:2/3*in_h[out8];[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:2/3*in_h[out9]"
\
-map "[out1]" out1.mp4 -map "[out2]" out2.mp4 -map "[out3]" out3.mp4 \
-map "[out4]" out4.mp4 -map "[out5]" out5.mp4 -map "[out6]" out6.mp4 \
-map "[out7]" out7.mp4 -map "[out8]" out8.mp4 -map "[out9]" out9.mp4

I expect the size of total 9 segments will be larger than the source video
since the search space of the segment became smaller and encoding
efficiency reduced. It is true for 720p and 1080p videos downloaded from
youtube. However, the size of total 9 segments for 1440p video and 4K video
became smaller compared with source video.

Can anyone please help me explain this situation?

Thanks.