Networked Media Open Specifications

AMWA BCP-005-01: EDID to NMOS Receiver Capabilities Mapping [Work In Progress]

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The purpose of AMWA BCP-005-01 is to provide Best Current Practice guidelines for mapping EDID fields to Receiver Capabilities in the case Receiver is associated with an Output connected to a downstream counterpart which provides EDID.

The proposed mapping provides the mechanism for converting EDID information into Receiver Capabilities. The effective Receiver Capabilities MAY differ from those obtained from the proposed mapping when the Receiver is:

The term ‘Receiver’ used in this document is defined in IS-04.

The terms ‘Parameter Constraint’ and ‘Constraint Set’ used in this document are defined in BCP-004-01.

The term ‘Output’ used in this document is defined in IS-11.

BCP-005-01 is intended to be used in conjunction with an IS-11 and BCP-004-01 deployment; however it has been written in such a way to provide useful functionality even in the absence of such a system.

This document is targeted against E-EDID which consist of EDID 1.4 (and covers EDID 1.3) and is referred to as Base EDID and the CTA-861 Extension Block imposed by HDMI.

Use of Normative Language

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

Video Receivers

If an IS-04 Video Receiver is associated with an Output which has an EDID, the optional mapping of the EDID supported video formats into Receiver’s Capabilities SHALL be performed according to the rules below.

Video Mode Mappings

Video modes, described in E-EDID, provide information about the video frame size and frame rate. There are multiple blocks which keep information about these modes, each has its own mapping requirements.

Each video mode SHOULD be expressed in the Receiver’s Capabilities as a separate Constraint Set or a part of a more common Constraint Set with non-empty

The video mode descriptors MAY include one or more of the following mappings:

Established Timings

Three blocks of Established Timings, described in the form of video mode lists, indicate support of industry de-facto video modes. Established Timings I and II are defined in E-EDID section 3.8 and Established Timings III in E-EDID section Both sections give information about frame width, height and rate and interlace mode for each of the listed video modes.


Standard Timings

Standard Timings describe industry de-facto video modes that are not listed in the Established Timings. Standard Timings format is defined in E-EDID section 3.9. The mapping is as follows:


Detailed Timing Descriptors (18 Byte Descriptors)

Defined in E-EDID section 3.10, there are 4 possible descriptors which can be provided. Each Detailed Timing Descriptor in Base EDID and CTA-861 Extension Block (section 7.2.1) MUST follow the mapping.

The mapping is defined in section 3.10.2 and is applied as follows:

CVT 3 Byte Codes

CVT 3 Byte Code structure is defined in E-EDID section

The Preferred Vertical Rate SHOULD be indicated by using a higher urn:x-nmos:cap:meta:preference value in Constraint Set(s) describing this value vs. other Supported Vertical Rates.

Short Video Descriptors

Short Video Descriptor (SVD) format is defined in CTA-861 section 7.5.1.

It operates with Video Identification Codes (VICs). Each of them is associated with a union of frame width, height and rate and interlace mode. This mapping is defined in CTA-861 section 4.1.

Vertical Frequency Discrepancy

E-EDID describes video timings which actual vertical frequency may not be equal to the grain rate of the corresponding video mode.

Established Timings, Standard Timings and CVT 3 Byte Codes operate with video mode descriptions with integer vertical frequencies although these video modes correspond to video timings with fractional vertical frequencies (some of these timings are described in DMT).

Describing such video modes in Receiver Capabilities is implementation specific and depend on what network stream the Receiver can handle. urn:x-nmos:cap:format:grain_rate in corresponding Constraint Set(s) MUST describe vertical frequency from either the video mode or the video timings and MAY describe both.

Some VICs (CTA-861 section 4.1) are marked as associated with two flavours of the same mode: with a vertical frequency that is an integer multiple of 6 Hz and a vertical frequency adjusted by a factor of 1000/1001. urn:x-nmos:cap:format:grain_rate in corresponding Constraint Set(s) MUST describe at least one of these vertical frequencies and MAY describe both.

Video Mode Preference

Constraint Sets for Detailed Timing Descriptors and Short Video Descriptors describing Native Video Formats MUST have higher urn:x-nmos:cap:meta:preference values than Constraint Sets for video modes not marked as native.

The Constraint Set for the first Detailed Timing Descriptor in Base EDID, called Preferred Timing Mode, or the Constraint Set for the first Short Video Descriptor in the first CTA-861 Extension if it takes precedence (CTA-861 section 7.5) MUST have the highest urn:x-nmos:cap:meta:preference value among the Constraint Sets.

Color Subsampling

If an E-EDID doesn’t have any CTA-861 Extensions, color subsampling formats MUST be taken from Base EDID, otherwise from the Extensions.


The origin of supported color subsampling formats in Base EDID is the Feature Support in E-EDID section 3.6.4.

It has one of four possible values:

This value MUST be transformed into urn:x-nmos:cap:format:color_sampling with enum values according to those permitted by capabilities Parameter Registry and MUST be added to each Constraint Set.

CTA-861 Extension

The supported color subsampling formats in the CTA Extension Header (CTA-861 section 7.5) indicate YCbCr-4:2:2 and YCbCr-4:4:4 support in addition to RGB.

YCbCr 4:2:0 Capability Map Data Block (CTA-861 section 7.5.11) shows which video modes support YCbCr-4:2:0 in addition to subsampling formats listed in the CTA Extension Header. Constraint Sets associated with these video modes MUST contain YCbCr-4:2:0 within the possible values for urn:x-nmos:cap:format:color_sampling.

YCbCr 4:2:0 Video Data Block (CTA-861 section 7.5.10) marks video modes as supporting only YCbCr-4:2:0. Constraint Sets associated with these video modes MUST have urn:x-nmos:cap:format:color_sampling limited to YCbCr-4:2:0.

Color Component Depth

Color Bit Depth of Video Input Definition described in E-EDID section 3.6.1 MUST be transformed into urn:x-nmos:cap:format:component_depth and MUST be added to each Constraint Set.

Vendor-Specific Data Block (CTA-861 section 7.5.4) SHOULD be transformed into urn:x-nmos:cap:format:component_depth if contains related information.


Colorimetry Data Block (CTA-861 section 7.5.5) SHOULD be transformed into urn:x-nmos:cap:format:colorspace with related information if present.

Audio Receivers

If the Basic Audio support bit is active in the CTA Extension Header, audio receiver MUST have Receiver Capabilities.

When no descriptors are provided, the capabilities MUST contain:

Short Audio Descriptors

If there are Short Audio Descriptors (see CTA-861 section 7.5.2), then each of them MUST be transformed into a Constraint Set.

Each of these Parameter Constraints MUST use enum Constraint Keyword.

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