Php Check if 2 from Database are empty

Hello I am working on simple video script where I need to do the following:

I need to check if Variable Source is empty (if it's not empty echo $source, but if it is empty proceed to check other variable below)

if Variable Embed is set, if it is set (echo $embed), but if it is empty do

echo $image

Basically I have setup system for Videos that can load either from Youtube Video with iframe, either with Embed from all kinds of other pages

but if Both of this fields are empty I need to show just image that will be set from URL