yt video size
bestvideo+bestaudio/best
4320p (8K) : 7680 × 4320 pixels
2160p (4K): 3840 × 2160 pixels
1080p (Full HD): 1920 × 1080 pixels
720p (HD): 1280 × 720 pixels
480p (Standard Definition): 854 × 480 pixels
360p : 640 × 360 pixels
240p : 426 × 240 pixels
144p: 256 × 144 pixels
YouTube videos generally use a 16:9 aspect ratio (widescreen)