audio format
all formats but "best" are converted, meaning that there'll be some quality loss. audio is not reencoded only when "best" format is selected.
audio bitrate
bitrate applies only to audio conversion. cobalt can't improve the source audio quality, so choosing a bitrate over 128kbps may inflate the file size with no audible difference. perceived quality may vary by format.
tiktok
cobalt will download the sound from the video without any changes by the post's author.
youtube
works even if cobalt isn't translated to your language.