Create a gif from a video using ffmpeg

gif.sh

#!/bin/sh

# Usage:
# gif.sh input output width fps

# Example:
# 12 frame per second
# 640 width (aspect ratio is preserved. Use -1 for no change)
# gif.sh input.mp4 output.gif 640 12

palette="/tmp/palette.png"
filters="fps=$4,scale=$3:-1:flags=lanczos"

# Generate a palette file for the most frequent colors in the input
ffmpeg -v warning -i $1 -vf "$filters,palettegen" -y $palette

# Convert the video to a gif using the palette and input parameters
ffmpeg -v warning -i $1 -i $palette -lavfi "$filters [x]; [x][1:v] paletteuse" -y $2