I know that the software is responsive but can i limit video size? because its so big on youtube videos and is hampering loading on large monitors.

yes, you can limit the size editing css

go to ACP -> customize -> themes -> CSS -> core - > global -> framework -> post-content.css

Then you change the size in the css under...

/* ======================================================== */
/* EMBEDDABLES - oEmbed Videos								*/
/* These styles are used for embedded links to oEmbed		*/
/* services that identify themselves as videos (for example	*/
/* YouTube, Vimeo and Hulu)									*/
/* ======================================================== */