Spatie\MediaLibrary\Conversion\Conversion::getResultExtension PHP Method

    public function getResultExtension(string $originalFileExtension = '') : string
    {
        return array_reduce($this->getManipulations(), function ($carry, array $manipulation) {
            if (isset($manipulation['fm'])) {
                $keepExtensions = ['jpg', 'jpeg', 'png', 'gif'];
                return $manipulation['fm'] === 'src' && in_array($carry, $keepExtensions) ? $carry : $manipulation['fm'];
            }
            return $carry;
        }, $originalFileExtension);
    }

 public function getPathRelativeToRoot() : string
 {
     if (is_null($this->conversion)) {
         return $this->pathGenerator->getPath($this->media) . $this->media->file_name;
     }
     return $this->pathGenerator->getPathForConversions($this->media) . $this->conversion->getName() . '.' . $this->conversion->getResultExtension($this->media->extension);
 }