VTSM VOB vs VMGM VOB: DVD Menu Differences

In standard DVD-Video architecture, interactive menus are handled by two distinct types of Video Object (VOB) files: the Video Manager Menu (VMGM) VOB and the Video Title Set Menu (VTSM) VOB. While both contain multiplexed video, audio, and subpicture streams used to render interactive buttons and backgrounds, they occupy different levels in the DVD hierarchy. This article outlines the key technical and structural differences between VMGM and VTSM VOB files, including disc scope, remote control mappings, and file organization.

Hierarchical Scope: Disc-Level vs. Title-Level

The primary difference lies in their operational scope within the DVD structure:

• VMGM VOB (Video Manager Menu): Functions at the global disc level. It acts as the master control hub for the entire DVD, meaning it can direct playback to any Title or Video Title Set (VTS) on the disc. It is typically used for disc-wide setup screens, language selection, or initial main menus.
• VTSM VOB (Video Title Set Menu): Functions strictly within the boundaries of a single Video Title Set. Its scope is localized, designed to control content exclusively within that specific VTS, such as scene selections (chapters), title-specific audio setups, or extras tied directly to that feature.

File Naming and Disc Location

Each menu type uses a specific naming convention in the DVD's VIDEO_TS directory:

• VMGM VOB: Stored as VIDEO_TS.VOB. It is governed by VIDEO_TS.IFO, which provides the navigation instructions for the disc manager. A DVD can only have one VMGM VOB file (split into 1 GB segments if necessary).
• VTSM VOB: Stored as VTS_xx_0.VOB, where xx represents the two-digit VTS number (e.g., VTS_01_0.VOB). It is governed by its corresponding VTS_xx_0.IFO file. Each VTS on the disc can have its own dedicated VTSM VOB.

Remote Control Button Mapping

Standard DVD players handle the physical buttons on the remote control differently depending on whether the command targets the VMGM or VTSM domain:

• Title Menu (Top Menu): Typically calls the VMGM domain. Pressing this button prompts the player to branch out of the current title and jump directly to the disc-level menu in VIDEO_TS.VOB.
• Root Menu (Menu): Typically calls the VTSM domain. Pressing this button jumps to the root menu within the currently playing title set (VTS_xx_0.VOB). While authors can remap this behavior using navigation commands, the specification standardizes Root Menus within the VTS domain.

Navigation and Linking Capabilities

The DVD specification enforces strict navigation rules between these domains:

• VMGM Navigation: A VMGM VOB can issue commands that jump directly to any title in any VTS across the disc. However, it cannot directly address individual cells or chapters inside a title without first entering the corresponding VTS domain.
• VTSM Navigation: A VTSM VOB can navigate freely within its own VTS (such as jumping to specific chapters or audio streams of its associated title). However, a VTSM cannot link directly to another VTS. To access a different title set, the navigation command must first exit to the VMGM, which then routes playback to the desired target.

Structural Sub-Menus

The DVD specification reserves specific menu types within each domain:

• VMGM Sub-Menus: Can include the Title Menu, as well as general setup menus applicable to the entire disc.
• VTSM Sub-Menus: Can be divided into standardized menu types within the title set, including Root, Subpicture, Audio, Angle, and Chapter (Part of Title) menus.