split

#!/bin/bash

step=15 ext=
opts_default=( -acodec copy -vn )

[[ -z "$1" || -z "$2" || "$1" = -h || "$1" = --help ]] && {
	cmd=$(basename "$0")
	echo >&2 "Usage:"
	echo >&2 "  $cmd file-to-split.mp3 prefix [ chunk-len-in-minutes ] [ ext ] [ ffmpeg opts ]"
	echo >&2 "  $cmd prefix [ chunk-len-in-minutes ] [ ext ] [ ffmpeg opts ] -- file1.mp3 file2.mp3 ..."
	echo >&2 "Example: $cmd some-long-book.mp3 slb"
	echo >&2 "Example: $cmd slb -- some-long-book-p1.mp3 some-long-book-p2.mp3 ..."
	echo >&2 "  Resulting files will be: slb-001.mp3 slb-002.mp3 ..."
	echo >&2 "  Default length: $step minutes"
	echo >&2 "  Default ffmpeg opts (only good for audio files!): ${opts_default[@]}"
	echo >&2 "  Special ffmpeg opts (must be before others, if any, in the same order):"
	echo >&2 "    -: don't pass default ones"
	echo >&2 "    -v: -c copy -bsf:a aac_adtstoasc"
	echo >&2 "Example (transcode to ogg): $cmd some-file.m4b sf-split 30 ogg -f ogg"
	echo >&2 "Example: $cmd sf-split 30 ogg - -new -ffmpeg -opts -f ogg -- some-file-1.m4b ..."
	exit 1
}

set -e -o pipefail


arg_opts=() arg_src=() arg_src_flag=
for arg in "$@"; do
	[[ "$arg" != -- ]] || { arg_src_flag=t; continue; }
	[[ -z "$arg_src_flag" ]]\
		&& arg_opts+=( "$arg" ) || arg_src+=( "$arg" )
done
[[ -n "$arg_src_flag" || "${#arg_opts[@]}" -eq 0 ]] || {
	arg_src+=( "${arg_opts[0]}" )
	arg_opts=( "${arg_opts[@]:1}" )
}

prefix=${arg_opts[0]}
[[ -n "$prefix" ]] || { echo >&2 "ERROR: no prefix specified"; exit 1; }
[[ -z "${arg_opts[1]}" ]] || step=${arg_opts[1]}
[[ -z "${arg_opts[2]}" ]] || ext=${arg_opts[2]}
step=$(( $step * 60 ))

opts=()
[[ -z "${arg_opts[3]}" ]] || {
	opts=( "${arg_opts[@]:3}" )
	[[ "${opts[0]}" != - ]] || { opts_default=(); opts=( "${opts[@]:1}" ); }
	[[ "${opts[0]}" != -v ]] || opts=( -c copy -bsf:a aac_adtstoasc "${opts[@]:1}" )
}
opts=( "${opts_default[@]}" "${opts[@]}" )


src_lens=()
for src in "${arg_src[@]}"; do
	len=$( ffprobe "$src" 2>&1 |
		awk 'match($0,/Duration: (\S+)\./,a) {split(a[1],b,":");print b[1]*3600+b[2]*60+b[3]}' )
	[[ -n "$len" && "$len" -gt 0 ]] || {
		echo >&2 "ERROR: Failed to get duration for: $src"; exit 1; }
	src_lens+=( "$len" )
done

[[ "${#arg_src[@]}" -eq 1 ]] && n_src= || n_src=0
for src in "${arg_src[@]}"; do
	len=${src_lens[${n_src:-0}]}
	[[ -n "$ext" ]] || ext=${src##*.}

	n=1
	ns=$(( ($len / $step) + 1 ))

	while [[ $n -le $ns ]]; do
		s=$(( ($n-1) * $step ))
		e=$(( $n * $step ))
		[[ -z "$n_src" ]] && dst= || dst="$(printf '%03d' $(( $n_src + 1 )))."
		dst+=$(printf '%03d' $n)
		dst="${prefix}-${dst}.${ext}"

		echo "---- $dst [$n/$ns, $s-$e]"

		ffmpeg -loglevel warning -y -i "$src" "${opts[@]}" -ss $s -to $e "$dst" </dev/null
		(( n += 1 ))
	done

	[[ -z "$n_src" ]] || (( n_src += 1 ))
done

: