How to use the @iiif/vocabulary.MediaType.WEBM function in @iiif/vocabulary

isVideoFormat(type: string): boolean {
        const videoFormats: string[] = [MediaType.VIDEO_MP4, MediaType.WEBM];
        return videoFormats.indexOf(type) != -1;
    }

load: this._extensions[Extension.OSD]
        };

        this._extensionRegistry[MediaType.PDF] = {
            load: this._extensions[Extension.PDF]
        };

        this._extensionRegistry[MediaType.AUDIO_MP4] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.VIDEO_MP4] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.WEBM] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.THREEJS] = {
            load: this._extensions[Extension.VIRTEX]
        };

        this._extensionRegistry[MediaType.MP3] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.M3U8] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.MPEG_DASH] = {