Pimcore\Model\Asset::addMetadata PHP Method

    public function addMetadata($name, $type, $data = null, $language = null)
    {
        if ($name && $type) {
            $tmp = [];
            if (!is_array($this->metadata)) {
                $this->metadata = [];
            }
            foreach ($this->metadata as $item) {
                if ($item["name"] != $name || $language != $item["language"]) {
                    $tmp[] = $item;
                }
            }
            $tmp[] = ["name" => $name, "type" => $type, "data" => $data, "language" => $language];
            $this->metadata = $tmp;
            $this->setHasMetaData(true);
        }
    }