There's typically a checkbox in the Add Multimedia dialogue for snap-to-proportions which should make the windowing for the video exactly on the correct bounds; there's also a checkbox area (under advanced options) for whether there is a border drawn around the video or not, and if yes, the stroke weight.
Where this lives and how it looks is extremely dependent upon which version of Acrobat Pro you're using (IX, XI, DC) so it's not worth the time for me to detail the where-in-the-menu-hierarchy-it-lives stuff - but I can tell you I just tested on my machine (Win 10, Acrobat XI Pro) and had no trouble controlling this parameter.
Hope this helps.