Convert ffprobe chapters to cuesheet

chapters2cue.php

#!/usr/bin/env php
<?php

/**
 * Convert ffprobe chapters to cuesheet.
 *
 * This is typically used in a video-to-audio transcoding job:
 *
 * - ffprobe -show_chapters -print_format json -loglevel -8 video.file > chapters.json
 * - ffmpeg -i video.file audio.file
 * - chapters2cue audio.file < chapters.json > cuesheet.cue
 * - shnsplit -f cuesheet.cue -o "flac flac -s -o %f -" audio.file
 * - cuetag cuesheet.cue *.flac
 */

define('FRAME_RATE', 75);

if (empty($argv[1])) {
  die("Usage: chapters2cue audio-filename.flac < chapter-filename.json > cue-filename.cue\n");
}

$filename = $argv[1];
$filetype = strtoupper(pathinfo($filename, PATHINFO_EXTENSION));

stream_set_blocking(STDIN, TRUE);
$chapters = json_decode(file_get_contents("php://stdin"), flags: JSON_THROW_ON_ERROR);
print("FILE \"$filename\" $filetype\n");
$start = 0;
foreach ($chapters->chapters as $n => $chapter) {
  $track = $n + 1;
  print("  TRACK $track AUDIO\n");
  $title = $chapter?->tags?->title ?? "Track $track";
  print("     TITLE \"$title\"\n");
  $timecode = secondsToTimecode((float) $chapter->start_time);
  print("     INDEX 01 $timecode\n");
}

function secondsToTimecode($seconds) {
  $mm = (int) floor($seconds / 60);
  $ss = (int) floor($seconds) % 60;
  $ff = (int) round(($seconds - floor($seconds)) * 1000 / FRAME_RATE);
  return sprintf("%02d:%02d:%02d", $mm, $ss, $ff);
}