#!/usr/bin/env bash

# Uses ffmpeg to convert a video file to a gif file. Optimizes the final result
# with gifsicle.
#
# Requires: ffmpeg
# Optional: gifsicle
#
# Example:
#   vid2gif some-vid.mp4 output.gif
#   vid2gif -f 10 -s 00:00:10 -t 00:00:05 some-vid.mp4 output.gif

set -e
PALETTE="/tmp/palette.png"

usage() {
    cat <<EOL
Usage: $0 [-fsth] [videofile] [destfile]

    -f [FPS]       set frames per second
    -s [hh:mm:ss]  set starting time (like -ss in ffmpeg)
    -t [hh:mm:ss]  set the duration to capture (like -t in ffmpeg)
    -h             this help
EOL
}

cleanup() { rm -f "$PALETTE"; }
trap cleanup EXIT

#
fps=30
while getopts hf:s:t: opt; do
    case $opt in
        f) fps="$OPTARG" ;;
        s) start="-ss $OPTARG" ;;
        t) duration="-t $OPTARG" ;;
        h) usage
            exit
            ;;
        :) >&2 echo "$OPTARG requires an argument"
            usage
            exit 1
            ;;
        *) >&2 echo "Not a valid arg: $opt"
            usage
            exit 1
            ;;
    esac
done
shift $((OPTIND-1))

#
if (($# == 0)); then
    >&2 echo "No movie file specified"
    exit
elif [[ ! -f $1 ]]; then
    >&2 echo "$1 does not exist"
    exit
fi

src="$1"
dest="${2:-${${src##*/}%.mov}.gif}"
flags="fps=${fps}"

# stats_mode=full favors motion, causing the resulting palette to better
# accomodate fades and transitions.
ffmpeg -v warning $start $duration -i "$src" -vf "$flags,palettegen=stats_mode=full" -y "$PALETTE"
ffmpeg -v warning $start $duration -i "$src" -i "$PALETTE" -lavfi "$flags [x]; [x][1:v] paletteuse" -y "$dest"

if command -v gifsicle >/dev/null; then
    gifsicle -O3 "$dest" -o "$dest"
fi