protected function getDriver() {
    $version = $this->getVersion();
    if ($this->isVersionIsGreaterOrEqual($version, array(0, 11, 0))) {
      return new Driver\FfmpegDriver();
    } else if ($this->isVersionIsGreaterOrEqual($version, array(0, 9, 0))) {
      return new Driver\FfmpegDriver10();
    } else if ($this->isVersionIsGreaterOrEqual($version, array(0, 8, 0))) {
      return new Driver\FfmpegDriver08();
    } else {
      return new Driver\FfmpegDriver06();
    }
  }