If you’re working on responsive websites, you may already be familiar with FitVids – a nice little jQuery plugin that allows for fluid-width video embedding. This morning I found there’s also a FitVids plugin for WordPress. Very easy to use, just install it, activate it, then go to Appearance > Fitvids.
If you’re not already using jQuery 1.7+ – and you should be fine if your WordPress install is 3.4 or above – tick the checkbox to add jQuery 1.7.2.
Then under jQuery Selector, enter the container element you want to apply FitVids to. It’s probably .post, but if you’re not sure .body always works. Then save changes and you’re done – FitVids should now be resizing videos as browser size changes.