I have already written a little jQuery snippet to resize videos but I came across an article by Chris Coyier with an approach that I thought worked a lot better. Though I did add a few tweaks to it:
Now your videos will only be resized if they are larger than the parent container. In the instance above, I have set the parent container to the paragraph tag surrounding the video (in WordPress, a paragraph tag is automatically added to each paragraph). If your site uses a different container, you can easily change that one line to the tag, ID or class of your parent container.
newWidth = el.parents( '.class-name' ).width(),