(M1 Mac Pro) Continous screenshots is slow / skip frames

[yoru1119]

I am watching a 2160p bluray remux video (file size 53.7GB), and wanted to do a continuous screenshots of a screen that's around 3 seconds.
I slowed down the video to 0.25x, but only got 31 .png screenshots. It seems like it skipped a lot of frames?
When change the setting of screenshot file format to .jpg, it gives 74 screenshots.
How can I get more screeshots with .png format??
Thanks!

The video that i wanted to do screenshot recorded with quicktime:
https://wetransfer.com/downloads/1301ff ... 100/911d1b

Video specs:


VLC version: 3.0.16
MacOS: Monterey 12.1
Macbook model: Mac Pro 16" 2021 (M1 Pro chip)