How to use the @iiif/vocabulary.MediaType.VIDEO_MP4 function in @iiif/vocabulary

// presentation 3

        this._extensionRegistry[MediaType.JPG] = {
            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] = {