Time offset in MM:SS format. Minutes are unbounded; seconds 00-59. Examples: 0:00, 15:30, 125:07. Appears as a child of <item>. ISO 8601 timestamp of when the item was last modified. Appears as a child of <channel>. Libsyn internal show ID. Appears as a child of <item>. Libsyn internal item ID. Appears as a child of <item>. Widescreen (16:9) episode artwork, suitable for use as a video thumbnail. The URL is carried on the <href> attribute, mirroring <itunes:image>. Appears as a child of <item>. Container of one or more <libsyn:ad-marker> entries describing ad insertion points.