I've found the problem, it's due to the colorspace used for coding the video.
Suzinak have used the RGB instead of the yuv422p. Ren'Py accelerate only the yuv420p or yuv422p.
All the others formats will be slow, even if you change from OpenGL to DirectX (See the Ren'Py doc).
The solution are to transcode all the videos to the correct colorspace.
I've use : ffmpeg -y -hide_banner -loglevel warning -i .\LR3-A7.webm -pix_fmt yuv420p -crf 5 .\new\LR3-A7.webm
This will give approximately the same size in video, but reduce the CPU comsumption by 50% in any video player and in the game.
I've transcoded the black and all CH3 at 60FPS video too proove.
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Mega
Extract in [game folder] and overwrite old files.
is this fix going to be applicable to CH 4 animations as well?