Caption Shortcode: what filter to change the image size?

Question

Doing a huge overhaul of my website mainly for page load performance, I want to filter the caption shortcode in the_content to load the thumbnail version of the image if wp_is_mobile() returns true. If not, load the size set in the shortcode.

What is the right filter to do so?

Answer 1

Maybe you should read this. It explains how to achieve what you are looking for. Be aware of wp_is_mobile() function if you are using any cache system, it would result in some unexpected behavior.