Supported Color Spaces in VOB Video Files

This article provides an overview of the color spaces and color encoding standards supported by the VOB (Video Object) container format. Because VOB is the core container format used for DVD-Video media, its internal video streams are governed strictly by MPEG-2 and MPEG-1 program stream specifications. Consequently, video content stored inside a standard-compliant VOB container relies on the YCbCr color model using the ITU-R BT.601 standard, utilizing 4:2:0 chroma subsampling and limited dynamic range.

The Primary Color Space: ITU-R BT.601 (YCbCr)

VOB files designed for DVD-Video playback do not support arbitrary modern color spaces such as BT.709 (used for HD) or BT.2020 (used for HDR). Instead, video stored in a VOB container relies on the ITU-R BT.601 (often referred to simply as Rec. 601) standard.

The color data is encoded in the digital YCbCr color space, which separates the image into:

• Y (Luma): The brightness information.
• Cb (Chroma Blue): The difference between blue and luma.
• Cr (Chroma Red): The difference between red and luma.

Depending on whether the target format is NTSC or PAL, specific color primaries and transfer characteristics apply under the BT.601 umbrella:

• NTSC (SMPTE 170M): Used for 525-line, 29.97 fps content (predominantly North America and Japan).
• PAL (EBU Tech 3213 / BT.470): Used for 625-line, 25 fps content (predominantly Europe and parts of Asia).

Chroma Subsampling

To reduce bandwidth while maintaining perceived image quality, standard-definition MPEG-2 video within VOB files strictly utilizes 4:2:0 chroma subsampling. In this configuration, color resolution is halved both horizontally and vertically relative to the luma channel. 4:2:2 and 4:4:4 profiles are not supported by the DVD-Video standard and will not be found in compliant VOB containers.

Bit Depth and Quantization Range

• 8-Bit Depth: VOB files only support an 8-bit color depth per channel (providing 256 possible discrete levels per component). Higher bit depths like 10-bit or 12-bit are unsupported.
• Limited (TV) Range: The video signal adheres to standard video quantization levels rather than full computer-range values (0–255). For the Luma channel (Y), valid values range from 16 to 235. For the Chroma channels (Cb and Cr), valid values range from 16 to 240, with 128 representing the neutral (achromatic) center. Values outside this band (0–15 and 236/241–255) are reserved for footroom and headroom.

Absence of Native RGB Support

Native RGB color spaces (such as sRGB or Adobe RGB) are not supported for MPEG-2 video streams inside compliant VOB files. Any RGB source content must be converted and downsampled into the 8-bit YCbCr Rec. 601 space using 4:2:0 subsampling prior to multiplexing into the VOB container.