How to resize mp4 animation in top header?

How can I set width and height of an mp4 animation in a top header?
At my under-construction site, , when we try to place an animated log in the top header, it will go in but at small size. We need it much bigger.
The primary theme is commonsinabox, which is responsive, but we also have the plugin "Responsive Add Ons."
We are using rtMedia.
The animated log has the following characteristics:
File URL:
File name: logo_red3_5_18_mpg4.mp4
File type: MP4 (video/quicktime)
File size: 679 kB
Length: 0:08
Bitrate: 695kb/s
Dimensions: 1280 × 720
The file resizes fine when played on differing screen sizes in Windows Media Player.
The WPMU plugins are as follows:
Installed WPMU DEV Plugins
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Does anyone have any advice?
Thank you.