AV1 Mastering Display Color Volume Metadata

This article provides an overview of the mastering display color volume (MDCV) metadata fields embedded in an AV1 video bitstream. These static metadata fields define the color capabilities and luminance boundaries of the reference monitor used during content mastering, aligning with SMPTE ST 2086 specifications to ensure accurate High Dynamic Range (HDR) tone mapping on consumer displays.

In the AV1 specification, mastering display color volume data is transported within a dedicated Open Bitstream Unit (OBU) called OBU_METADATA, identified by the metadata type METADATA_TYPE_HDR_MDCV. The syntax structure contains the following specific fields:

1. primary_chromaticity_x and primary_chromaticity_y

• Size: 16 bits each (array of 3 elements for both x and y).
• Description: These fields specify the normalized CIE 1931 xy chromaticity coordinates of the three color primaries (Red, Green, and Blue) of the mastering display.
• Values: The index values [0], [1], and [2] correspond to the Green, Blue, and Red primaries, respectively. The coordinates are stored as 16-bit fixed-point values calculated by multiplying the normalized xy value by 50,000 (meaning one unit represents 0.00002). The valid range is 0 to 50,000.

2. white_point_chromaticity_x and white_point_chromaticity_y

• Size: 16 bits each.
• Description: These fields define the CIE 1931 xy chromaticity coordinates of the white point of the mastering display (typically targeting standard illuminants like D65).
• Values: Similar to the color primaries, these coordinates are normalized and scaled by a factor of 50,000, mapping the fractional coordinates into a 16-bit unsigned integer range from 0 to 50,000.

3. luminance_max

• Size: 32 bits.
• Description: Specifies the nominal maximum display luminance of the mastering monitor.
• Format: This value is represented as a 24.8 fixed-point number, consisting of a 24-bit integer part and an 8-bit fractional part. The luminance is expressed in candelas per square meter (\(\text{cd/m}^2\), or nits).

4. luminance_min

• Size: 32 bits.
• Description: Specifies the nominal minimum display luminance of the mastering monitor (the black level).
• Format: This value is represented as an 18.14 fixed-point number, containing an 18-bit integer part and a 14-bit fractional part. It is also expressed in candelas per square meter (\(\text{cd/m}^2\)).