Gifski converts video frames to GIF animations using pngquant's fancy features for efficient cross-frame palettes and temporal dithering. It produces animated GIFs that use thousands of colors per frame.
Release : https://github.com/ImageOptim/gifski/releases
I haven't finished implementing proper video import yet, so for now you need ffmpeg to convert video to PNG frames first:
ffmpeg -i video.mp4 frame%04d.png
and then make the GIF from the frames:
gifski -o file.gif frame*.png
See gifski -h for more options. The conversion might be a bit slow, because it takes a lot of effort to nicely massage these pixels. Also, you should suffer waiting like the poor users who will be downloading these huge files.