Mandatory Audio Codecs for DVD-Video VOB Files

The DVD-Video specification strictly defines which audio formats can be multiplexed into standard Video Object (VOB) containers to guarantee playback compatibility across all standalone players. To ensure universal playback, the standard mandates that every commercial DVD-Video disc must include at least one primary audio track encoded in a baseline format specific to the television system standard (NTSC or PAL) of the release.

Mandated Audio Codecs by Region

The DVD Forum established distinct baseline requirements depending on whether a disc is authored for NTSC or PAL/SECAM territories. At least one stream in the VOB file must use one of the following mandated formats:

• NTSC Discs: Must contain at least one audio stream encoded in either Dolby Digital (AC-3) or uncompressed Linear PCM (LPCM).
• PAL Discs: Must contain at least one audio stream encoded in Dolby Digital (AC-3), MPEG-1 Audio Layer II (MP2), or uncompressed Linear PCM (LPCM).

While MPEG-1 Audio Layer II was originally intended to be the primary multichannel standard for PAL, the DVD Forum updated the specification so that all PAL players must decode Dolby Digital, making AC-3 the de facto universal standard worldwide.

Overview of Mandated Codecs

• Dolby Digital (AC-3): The most common codec used in DVD authoring. It supports mono, stereo, and discrete 5.1 surround sound. It operates at sample rates of 48 kHz with bitrates ranging from 64 kbps up to 448 kbps.
• Linear PCM (LPCM): An uncompressed, lossless audio format based on raw pulse-code modulation. It supports 1 to 8 channels (typically stereo) at 48 kHz or 96 kHz sampling rates, with bit depths of 16-bit, 20-bit, or 24-bit. Due to high bitrates (up to 6.144 Mbps), it is typically reserved for music releases.
• MPEG-1 Audio Layer II (MP2): A lossy stereo format officially permitted as a primary audio track only on PAL standard discs. It operates at a fixed sample rate of 48 kHz with bitrates typically between 192 kbps and 384 kbps.

Optional Secondary Codecs

The DVD specification allows additional audio streams inside a VOB file, but these cannot be the sole audio track on the disc:

• DTS (Digital Theater Systems): Widely used for higher-bitrate 5.1 surround sound (typically 754 kbps or 1509 kbps). A disc featuring a DTS track must also include an AC-3 or LPCM track for fallback compatibility.
• MPEG-2 Multichannel: An extension of MP2 designed to support 5.1 surround sound, though it saw virtually zero commercial adoption.
• SDDS (Sony Dynamic Digital Sound): Permitted in the official technical specifications, but practically nonexistent on commercial consumer DVD-Video releases.