Convert a video to a looping GIF image using ffmpeg

mkgif.sh

#!/bin/bash

# Usage:
# ./mkgif.sh video.mkv [anim.gif] [frame_rate]

video_input="$1"
gif_output="$2"

print_error_and_exit() {
  echo "Error: $1" >&2
  exit 1
}

if [ -z "$video_input" ]; then
  print_error_and_exit "No input video provided."
fi

# Output filename?
if [ -n "$2" ] && [[ "$2" =~ ^[0-9]+(\.[0-9]+)?$ ]]; then
  frame_rate="$2"
  gif_output="${video_input%.*}.gif"
elif [ -n "$2" ]; then
  gif_output="$2"
else
  gif_output="${video_input%.*}.gif"
fi

if [ -n "$3" ]; then
  frame_rate=$3
else
  original_frame_rate=$(ffprobe -v 0 -of csv=p=0 -select_streams v:0 -show_entries stream=r_frame_rate "$video_input" | awk -F'/' '{print $1 / $2}')
  if [ -z "$original_frame_rate" ]; then
    print_error_and_exit "Failed to retrieve frame rate from video."
  fi

  # Linear interpolation for gif framerate
  min_fps=10
  max_fps=60
  if (( $(echo "$original_frame_rate <= $min_fps" | bc -l) )); then
    divisor=1
  elif (( $(echo "$original_frame_rate >= $max_fps" | bc -l) )); then
    divisor=4
  else
    divisor=$(echo "1 + ($original_frame_rate - $min_fps) * (3 / ($max_fps - $min_fps))" | bc -l)
  fi

  frame_rate=$(echo "$original_frame_rate / $divisor" | bc -l)
fi

echo "Encoding GIF at $frame_rate FPS..."
# TODO: Variable output width
ffmpeg -v warning -i "$video_input" -vf "fps=$frame_rate,scale=320:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" -loop 0 -y "$gif_output" || print_error_and_exit "FFmpeg failed to encode GIF."

echo "GIF successfully created at $gif_output"