How DVD Bonus Features Map to Secondary VOB Files

On a DVD-Video disc, bonus features and deleted scenes are mapped to secondary Video Object (VOB) files through a structured layout of Video Title Sets (VTS) orchestrated by Information (IFO) files. Rather than being loose media files, extras are multiplexed MPEG-2 streams assigned to dedicated titles and program chains (PGCs). This article explains how the DVD file architecture designates specific VTS numbers, menus, and sectors to deliver supplemental content separately from the main feature.

The Role of Video Title Sets (VTS)

A standard DVD stores all its data within the VIDEO_TS directory using three file types: VOB (audio/video streams), IFO (navigation data), and BUP (backups of the IFO files). Content on a disc is compartmentalized into Video Title Sets.

The primary film typically occupies the first title set:

• VTS_01_0.IFO: Navigation instructions for the main feature.
• VTS_01_0.VOB: Menu assets for the main feature.
• VTS_01_1.VOB through VTS_01_X.VOB: The continuous stream of the main movie, split into 1 GB segments due to file system limits.

Supplemental materials like deleted scenes, audio commentaries, and making-of featurettes are segregated into secondary title sets, such as VTS_02_X.VOB, VTS_03_X.VOB, and higher. Authoring software separates these assets because bonus features often use different technical specifications than the main movie, such as a 4:3 aspect ratio instead of 16:9 widescreen, stereo audio instead of 5.1 surround sound, or different subtitle configurations. Because all content within a single VTS must share the same video attributes, distinct extras require their own distinct VTS allocations.

How Menus Link to Secondary VOBs

VOB files do not contain playback logic; they only contain the interleaved audio, video, and subpicture packets. Navigation is controlled entirely by the IFO files.

When a user accesses a "Bonus Features" menu:

1. Menu Call: The main menu (VIDEO_TS.VOB or VTS_01_0.VOB) registers a user button press linked to a command (e.g., JumpTT Title_2).
2. IFO Pointer Translation: The disc player reads the master table (VIDEO_TS.IFO) or local table (VTS_02_0.IFO) to locate the requested title number.
3. Sector Addressing: The IFO file points directly to the Logical Block Address (LBA) on the physical disc where the secondary VOB (e.g., VTS_02_1.VOB) begins.
4. Playback via Program Chains (PGCs): The IFO designates which Program Chain within that VOB to execute, allowing individual deleted scenes to be played one by one or continuously via a "Play All" instruction.

Alternate Mapping: Titles Within the Same VTS

While dedicated title sets are standard, DVD authors occasionally map deleted scenes inside the same VTS as the main movie (e.g., VTS_01_X.VOB), placed in sectors after the main feature concludes. In this configuration, the main movie is defined as Title 1, and each deleted scene is registered as Title 2, Title 3, and so on, inside VTS_01_0.IFO. This method is used when the extra features share the exact same video resolution, aspect ratio, and audio encoding profile as the main film.

Standalone Extras vs. Seamless Branching

Deleted scenes generally follow one of two authoring techniques:

• Discrete Secondary VOBs: The deleted scenes exist exclusively as separate titles in distinct VOB files. Selecting a deleted scene simply routes the player to that file and returns to the menu upon completion.
• Seamless Branching (Shared VOBs): When deleted scenes can be watched integrated into an "Extended Edition" of the movie, the scenes are interleaved directly inside the primary movie VOBs (VTS_01_X.VOB). The IFO controls which video blocks (Interleaved Video Units, or ILVUs) the player reads. In standard playback, the laser skips the deleted scene blocks; in extended playback, the player reads them seamlessly without physical disc jumping.