Core Data Streams Multiplexed in a VOB Container

A VOB (Video Object) file is the core container format used in DVD-Video media, derived from the MPEG-2 Program Stream specification. It allows distinct multimedia components—including digital video, multi-channel audio tracks, sub-picture overlays, and navigational metadata—to be interleaved into a single, time-synchronized file. This article details the specific core data streams that can be multiplexed simultaneously within a standard VOB container.

1. Primary Video Stream

A VOB container supports exactly one primary video stream. This stream is encoded using either standard MPEG-2 (ISO/IEC 13818-2) or legacy MPEG-1 (ISO/IEC 11172-2). In DVD authoring, MPEG-2 is almost universally used, supporting both Constant Bitrate (CBR) and Variable Bitrate (VBR) profiles to balance visual quality and storage limitations.

2. Audio Streams

A single VOB file can simultaneously carry up to eight separate audio streams. These independent tracks enable alternate languages, director commentaries, and audio descriptions. The container multiplexes audio encoded in several standardized formats:

• Dolby Digital (AC-3): The most common standard, supporting mono up to 5.1 surround sound.
• Linear PCM (LPCM): Uncompressed audio offering high fidelity, typically in 16-bit or 24-bit stereo.
• DTS (Digital Theater Systems): An optional multichannel surround sound format offering higher bitrates than AC-3.
• MPEG-1 Audio Layer II / MPEG-2 Audio: Used primarily in PAL territories as an alternative stereo or multichannel standard.

3. Sub-picture Streams

A VOB container can multiplex up to 32 distinct sub-picture streams. Unlike plain text subtitles, DVD sub-pictures are run-length encoded 2-bit bitmap graphics with 4-color palettes. These streams serve several simultaneous purposes:

• Multilingual subtitles and closed captioning.
• Interactive menu button highlights and states (normal, selected, activated).
• Visual cues, such as karaoke lyrics.

4. Navigation and Control Data

To facilitate user interaction and DVD playback features, a VOB stream multiplexes critical control packets alongside media data:

• Presentation Control Information (PCI): Contains data controlling real-time presentation, such as menu button coordinates, angle-switching triggers, and non-seamless branch timing.
• Data Search Information (DSI): Contains navigational pointers, forward and backward jump addresses, and timecodes that allow seamless playback, fast-forwarding, rewinding, and audio/video synchronization across the disc sectors.