video quality
if preferred video quality isn't available, next best is picked instead.
youtube video codec and container
h264: best compatibility, average bitrate. max quality is 1080p.
av1: best quality, efficiency, and bitrate. supports 8k & HDR.
vp9: same quality & bitrate as av1, but file is approximately two times bigger. supports 4k & HDR.
av1 and vp9 aren't as widely supported as h264.
twitter/x
GIF conversion is inefficient, converted file may be obnoxiously big and low quality.
tiktok
allows downloading videos in 1080p at cost of compatibility.