On whitelisted sites enables autodetection only on sites you explicitly whitelisted.
Never disables autodetection on all sites, even on those you whitelisted.
Advanced automatic detection options
Options here decide how often the extension will check for changes in aspect ratio of a given video.
Values are given in milliseconds. Longer intervals increase delay between aspect ratio changing and extension re-correcting for the change. Using shorter intervals than the default ones can cause lage and immense RAM usage.
In order for autodetection to work, the extension grabs a frame of the video you're watching and takes a look at it. Some websites use DRM, which prevents you from using the HTML5-blessed way of getting a frame from a video. Some browsers offer some features that can be used to circumvent DRM protection. With this option enabled, the extension will use said features to basically do that.
At the moment, Firefox is the only browser to support this.