WEBM, is it the default option of yt-dlp downloads?

[Linux for blind general discussion]

Hello friends,

I noticed that all of my downloads from youtube and facebook using 
yt-dlp come in a WEBM format.  Is WEBM the default option of yt-dlp or 
is it the only option?

How can I change the setting to make sure that my downloads maintain 
their original formats without changes. I want my downloads to be mp3 if 
the original is mp3, or mp4 if the original is mp4...etc. Is this possible?

Cheers,

Ibrahim