Convert GIF using ffmpeg and ImageMagick

gistfile1.sh

# Use ffmpeg to decode input video (GIF in this case)
ffmpeg -i input.gif decode/%d.png

# Use ImageMagick to crop, format: (W)x(H)+(W_SFHIT)+(H_SHIFT)
# Note the {from..to..skip} usage of Bash
convert decoded/{1..759..5}.png -crop 315x172+20+40 resized/%d.png

# An resize option
# convert decoded/{1..759..5}.png -crop 315x172+20+40 -resize 30% resized/%d.png

# (Optional) Tune brightness/saturation/contrase
# convert decode/{1..759..5}.png -modulate 200,150 -contrast-stretch 1% converted/%d.png

# Generate GIF. delay=10 if for browser, loop=0 means infinite.
convert -delay 10 -loop 0 resized/{1..151..3}.png output.gif