Gifski is the highest-quality video to GIF converter.
GIFs don't have to look like a dog ate them. Gifski creates GIFs with smooth gradients, correct colors, and rarely any dithering.
Just drag and drop to convert!
The app is for macOS 10.13 or later.
This extension is primarily for UltraWide monitors, but that does not mean it's only good for it. You can manipulate the size of the video that contains horizontal or vertical black bars and let the video fill your entire screen for a better experience.