how can I change

how can I change the default size of the video layout. Currently it is this [video width="1280" height="720" mp4="http://s3-us-west-1.amazonaws.com/excelcoupon1ca/wp-content/uploads/sites/18/2016/12/11072234/keep.mp4"][/video]

I would like to change it to whatever I choose; such as, [video width="180" height="120"
Thank you