The multimedia macro has some controls to supposedly set the size of the file .. all that seems to do is control the size of the black background box, but not the size of playing window

The playing window seems to be a fixed size with what seems to be a non-functioning "Full Screen" size button.

So what I see is a video occupying ~25% of my screen - I have to zoom my complete browser window to get something that is view-able

It seems that you just need to enable the View Full Screen button

Also seems a similar issue reported here has been closed to lack of interest

In my case I am managing a Confluence instance with 5000 Users and we are about to launch various video files so please count my single vote as 5000 votes!!  I hope that is interest enough???

https://jira.atlassian.com/browse/CONFSERVER-34159