Use DisableMonitor (https://github.com/Eun/DisableMonitor) as a free tool to adjust your Macbook Retina Display to any custom resolution, including 16:9 aspect ratio.
Forget SwitchResX charging you around $20 for it.
Use DisableMonitor, which is absolutely free.
This tutorial will teach you how to set the internal monitor resolution to 1920x1080 or 1280x720 (Full HD). This will work with any version of OS X, including El Capitan. Also works with external monitors, and is a great tip if you want to record a screencast for video tutorials to publish on YouTube or other online platforms that may require the right ratio.
