Converts gif image to webm (vp9) video

gif2webm.sh

#!/bin/bash

# Copyright (c) 2018 Alexander Tomilov
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

help() {
	echo "Convert gif image to webm/vp9 video."
	echo
	echo "Usage: $(basename "$0") [-crf crf_value] GIF_FILE [GIF_FILE...]"
	echo
	echo "The CRF value must be from 0--63."
	echo "If undefined, the value will be determined automatically."
}

define_crf() {
	h=$(identify -format "%h" "$1[0]")
	if [ "$?" -ne 0 ]; then
		exit 1
	fi

	# Quality values from:
	# https://developers.google.com/media/vp9/settings/vod/#recommended_settings
	if [ "$h" -lt 300 ]; then
		return 34 # 480p (low) quality
	elif [ "$h" -lt 800 ]; then
		return 32 # 720p quality
	elif [ "$h" -lt 1000 ]; then
		return 31 # 1080p quality
	elif [ "$h" -lt 1500 ]; then
		return 24 # 1440p quality
	else
		return 15 # 2160p quality
	fi
}

if [ \( $# -lt 1 \) -o \( "$1" = "--help" \) ]; then
	help
	exit 0
fi

crf=-1
if [ "$1" = "-crf" ]; then
	if [ \( "$2" -lt 0 \) -o \( "$2" -gt 63 \) ]; then
		echo "The CRF value must be from 0--63!"
		exit 1
	fi
	crf="$2"
	shift 2
fi

for gif in "$@"; do
	if [ \( ! -f "$gif" \) -o \( "$(file --mime-type -b "$gif")" != "image/gif" \) ]; then
		echo "$gif isn't a gif image!"
		exit 1
	fi
done

for gif in "$@"; do
	if [ "$crf" = -1 ]; then # auto CRF definition
		define_crf "$gif"
		cur_crf="$?"
	else
		cur_crf="$crf"
	fi

	echo -e "\n\e[1;31m### $gif"
	echo -e "### CRF=${cur_crf}\e[0m"
	ffmpeg -hide_banner -i "$gif" -c:v libvpx-vp9 -b:v 0 -crf "$cur_crf" "${gif}.webm"
done