Owncast chat log to ASS/SSA subtitles

owncast-chat2ass.sh

#! /bin/sh
# owncast-chat2ass.sh
# Copyright (c) 2023 vftdan (https://github.com/Vftdan)

TimeToSeconds() {
	date -d "$1" +'%s.%N'
}

TimespanSeconds() {
	printf '%s\n' "$(TimeToSeconds "$2") - $(TimeToSeconds "$1")" | bc
}

SecondsToTimeWithCS() {
	# CS = centisecond
	# Wraps at 24h!!!
	date -ud "@$1" +'%T.%N' | sed -E 's/^0?//; s/[0-9]{7}$//'
}

EscapeRtf() {
	sed -E 's/[\\{}]/\\\0/g; s/$/\\n/g' | tr -d '\n' | head -c -2
	echo
}

HtmlToRtf() {
	sed -E 's/<(em|i)>/{\\i1}/g; s/<\/(em|i)>/{\\i0}/g; s/<(b|strong)>/{\\b1}/g; s/<\/(b|strong)>/{\\b0}/g; s/\&gt;/>/g; s/\&lt;/</g; s/\&\#39;/'"'"'/g; s/\&quot;/"/g; s/\&amp;/\&/g'
}

SanitizeSSACSVValue() {
	tr -d ',\n'
}

PrintSSACSVSanitizedValue() {
	printf '%s,' "$(printf '%s\n' "$1" | SanitizeSSACSVValue)"
}

ExtractMessages() {
	jq -c '.[] | select(.type == "CHAT") | {"timestamp": .timestamp, "user": .user.displayName, "text": .body}'
}

PrintSSAINISection() {
	printf '[%s]\n' "$1"
}

PrintSSAINIKeyPrefix() {
	printf '%s: ' "$1"
}

PrependLinesSSAINIKey() {
	while read -r line; do \
		PrintSSAINIKeyPrefix "$1"
		printf '%s\n' "$line"
	done
}

MessageToSSAEventCSV() {
	local timestamp="$(printf "%s" "$2" | jq -r '.timestamp')"
	local user="$(printf '%s' "$2" | jq -r '.user')"
	local text="$(printf '%s' "$2" | jq -r '.text')"
	local secfromstart="$(TimespanSeconds "$vodstart" "$timestamp")"
	local endsecfromstart="$(printf '%s\n' "$secfromstart + $1" | bc)"
	# Layer:
	PrintSSACSVSanitizedValue 0
	# Start:
	PrintSSACSVSanitizedValue "$(SecondsToTimeWithCS "$secfromstart")"
	# End:
	PrintSSACSVSanitizedValue "$(SecondsToTimeWithCS "$endsecfromstart")"
	# Style:
	PrintSSACSVSanitizedValue Default
	# Name:
	PrintSSACSVSanitizedValue "$user"
	# MarginL:
	PrintSSACSVSanitizedValue 0
	# MarginR:
	PrintSSACSVSanitizedValue 0
	# MarginV:
	PrintSSACSVSanitizedValue 0
	# Effect:
	PrintSSACSVSanitizedValue 'Scroll up;300;200;25'
	# Text:
	printf '%s: %s\n' "$user" "$text" | EscapeRtf | HtmlToRtf
}

FlatMapLines() {
	while read -r line; do \
		"$@" "$line"
	done
}

Main() {
	PrintSSAINISection "Script Info"

	echo '; Script generated by owncast-chat2ass.sh'
	echo '; Shellscript author: https://github.com/Vftdan'

	PrintSSAINIKeyPrefix Title
	echo 'Default Aegisub file'

	PrintSSAINIKeyPrefix ScriptType
	echo 'v4.00+'

	echo
	PrintSSAINISection Events

	PrintSSAINIKeyPrefix Format
	echo 'Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text'
	ExtractMessages | FlatMapLines MessageToSSAEventCSV 2 | PrependLinesSSAINIKey Dialogue
}

PrintUsage() {
	echo "Usage: $0 <vod_start_timestamp>"
	echo 'VOD start timestamp must be provided in the format understood by date(1)'
	echo 'JSON file in the format like returned by https://${OWNCAST_SERVER}/api/chat?accessToken=${YOUR_ACCESS_TOKEN} must be piped into the standard input'
	echo 'Minimal SSA/ASS subtitle file will be printed to the standard output'
}

if [ $# -ne 1 ]; then \
	PrintUsage >&2
	exit 1
fi

case "$1" in
	-h|--help)
		PrintUsage
		exit 0
		;;
esac

export vodstart="$1"
Main