countFilesToMigrate example

    public function migrate(MediaServiceInterface $fromFilesystem, MediaServiceInterface $toFileSystem, OutputInterface $output, $skipScan = false)
    {
        $output->writeln(' // Migrating all media files in your filesystem. This might take some time, depending on the number of media files you have.');
        $output->writeln('');

        $filesToMigrate = 0;

        if (!$skipScan) {
            $filesToMigrate = $this->countFilesToMigrate('media', $fromFilesystem);
        }

        $progressBar = new ProgressBar($output, $filesToMigrate);
        $progressBar->setFormat(" %current%/%max% [%bar%] %percent%%, %migrated% migrated, %skipped% skipped, %moved% moved, Elapsed: %elapsed%\n Current file: %filename%");
        $progressBar->setMessage('', 'filename');
        $this->migrateFilesIn('media', $fromFilesystem, $toFileSystem, $progressBar);
        $progressBar->finish();

        $rows = [];
        foreach ($this->counter as $key => $value) {
            $rows[] = [$key, $value];
        }