How to resize JPEG using FFMPEG.

ffmpeg -i TREE.JPG -y -vf scale=iw*.2:ih*.2 tree.jpg

Another option is to set resolution.

ffmpeg -i TREE.JPG -y -vf scale=-1:720 tree.jpg

How to resize video using FFMPEG.

ffmpeg -i TREE.MP4 -s 640x360 -pix_fmt yuv420p -crf 18 tree.mp4

How to create a thumbnail from a video.

ffmpeg -ss 00:00:00 -i tree.mp4 -vframes 1 tree.jpg