How to put an image on top of video using ffmpeg? +scale video

Question

What i have :

png picture dem.png (not transparent) and video cat.mp4. I need to put this png as a background to video with resizing video inside.

Current result :

by executing :

ffmpeg -i cat.mp4 -framerate 30 -i dem.png -filter_complex "[1][0]overlay=x=100:y=100" -c:a copy -movflags +faststart out2.mp4

How can i scale mp4 in case i know paddings/required height/width of scaled mp4 here?

Very beginner in ffmpeg. I know, i need to use scale param, but can't understand how to do it with my current ffmpeg command.

Maybe someone know how to do it?

Files are here if you need : https://drive.google.com/drive/folders/1gKJCyVU0IgJ8g3zWFhCA-L93lDOWyOS-?usp=sharing

Answer 1

This works like a charm :

ffmpeg -y -i cat.mp4 -framerate 20 -i dem.png -filter_complex "[0:v]scale=512x397,setsar=1[v0];[1][v0]overlay=x=45:y=45" -c:a copy -movflags +faststart out2.mp4

Result will be :

If anyone can step-by-step describe what each part of command do - will appreciate!