<?php
namespace My\Project;

use \GetId3\GetId3Core as GetId3;

class MyClass
{
    // ...
    private function myMethod()
    {
        $mp3File = '/path/to/my/mp3file.mp3';
        $getId3 = new GetId3();
        $audio = $getId3
            ->setOptionMD5Data(true)
            ->setOptionMD5DataSource(true)
            ->setEncoding('UTF-8')
            ->analyze($mp3File)
        ;

        if (isset($audio['error'])) {
            throw new \RuntimeException(sprintf('Error at reading audio properties from "%s" with GetId3: %s.', $mp3File, $audio['error']));
        }
        $this->setLength(isset($audio['playtime_seconds']) ? $audio['playtime_seconds'] : '');

        // var_dump($audio);
    }
}