Change Youtube embed dimensions

[anon2020]

How can I change the dimensions of the youtube videos embedded in the posts, so that they take up less than 100% width?

For example a maximum width of 640 pixels.

[Morrigan]

System > Settings > Posting > Maximum video content width

I don't remember if its retroactive though.

[anon2020]

Thank you @Morrigan, I was confused. I was thinking I'd have to make some css modifications.

[Morrigan]

No problem dear.