Extract SRT subtitles from MKV files

extract-subtitles

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

declare(strict_types = 1);

if (count($argv) !== 2) help();
$dirname = $argv[1];
if (!is_dir($dirname)) help();

$directory_path = realpath($dirname);
$dir = new DirectoryIterator($directory_path);
foreach ($dir as $file) {
  if (!$file->isDot() && $file->isFile()) {
    $filename = $file->getFilename();
    $path = $file->getPathname();
    if (substr($filename, -4) === '.mkv') {
      foreach (subtitle_tracks($path) as $track) {
        extract_subtitles($path, $track);
      }
    }
  }
}

function subtitle_tracks(string $path): array {
  $tracks = [];
  $output = `mkvmerge -i {$path} | grep subtitles`;
  
  foreach (explode(PHP_EOL, $output) as $line) {
    if (preg_match('/Track ID (\d+): subtitles \(SubRip\/SRT\)/', $line, $matches)) {
      $tracks[] = (int) $matches[1];
    }
  }
  return $tracks;
}

function extract_subtitles(string $path, int $track): void {
  $subtitle_path = preg_replace('/.mkv$/', ".$track.srt", $path);
  if (is_file($subtitle_path)) {
    print "File $subtitle_path exists. Skipping.\n";
    return;
  }
  passthru("mkvextract tracks {$path} {$track}:{$subtitle_path}");
}

function help(): void {
  print "Usage: ./extract-subtitles.php <dir>\n";
  exit(0);
}