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A capability advertisement, not a command
EDID is data supplied by a display or downstream AV device. A source reads it and chooses a format it believes the complete signal path can support.
Base EDID block
A fixed 128-byte EDID 1.x structure containing identity, physical and color characteristics, timing declarations, four 18-byte descriptors, extension count, and checksum.
CTA-861 extension
Adds consumer-video formats, audio, speakers, HDR/colorimetry, YCbCr 4:2:0 signaling, and organization-specific capabilities.
DisplayID
A flexible VESA data-block framework for detailed display attributes, multiple timing representations, interfaces, tiled displays, adaptive sync, and more.
EDID 1.4
The 128-byte base block
The layout is fixed. Select a region to see what it encodes and what usually goes wrong.
00h–07hRecognition pattern
EDID header
The base block starts with the fixed sequence below. A different value means the input is not a normal EDID 1.x base block.
00 FF FF FF FF FF FF 00
Check Reject malformed data before interpreting any later field.
Four 18-byte descriptor slots
If the first two bytes are nonzero, the slot is a Detailed Timing Descriptor. If they are zero, the descriptor tag identifies monitor information.
For EDID 1.4, the first descriptor carries the preferred timing; detailed timings precede display descriptors.
Checksum math
Each 128-byte EDID block is valid at the checksum level when its unsigned byte sum is zero modulo 256.
(Σ block[0…127]) mod 256 = 0To generate the final byte:
checksum = (−Σ block[0…126]) & FFhRaster timing
A resolution is not a complete timing
A mode also needs blanking, sync placement, polarity, scan type, and a pixel clock. Two “1920 × 1080 at 60 Hz” timings can differ at the transport level.
Progressive approximationpixel clock = H total × V total × frame rate
Detailed Timing Descriptor
Stores pixel clock, active and blanking dimensions, sync offsets and widths, image size, borders, flags, and scan characteristics in 18 bytes.
Use when the exact waveform matters.DMT
VESA Display Monitor Timings is a catalog of established timing definitions. A DMT identity refers to a defined set of parameters, not merely width and height.
Useful for known computer-display modes.CVT 2.1
VESA’s formula method defines standard CRT-based timing and Reduced Blanking versions 1, 2, and 3 for non-CRT displays.
Inputs become a reproducible complete timing.CTA VIC / SVD
A Short Video Descriptor advertises a CTA Video Identification Code. The code points to a format defined by CTA-861.
Common for television and AV formats.CTA-861-H
The extension most AV systems depend on
The CTA extension uses tag 02h. Its compact Data Block Collection advertises video, audio, speakers, color/HDR behavior, and vendor-defined capabilities.
Video Data Block
Contains one-byte Short Video Descriptors. Each SVD carries a VIC and, where defined by the encoding, a native-format indication.
Audio Data Block
Contains three-byte Short Audio Descriptors describing format, channel count, sample rates, and a format-dependent third byte.
Speaker Allocation
Declares speaker-position support. It complements audio formats; it does not replace the channel count encoded in each SAD.
Vendor-Specific Blocks
Begin with an IEEE organization identifier and use that organization’s definition. HDMI Licensing and HDMI Forum blocks are common examples.
HDR Static Metadata
Advertises EOTF and static-metadata support. Desired-content maximum, frame-average, and minimum luminance bytes are ordered and optional.
YCbCr 4:2:0 Blocks
Y420VDB lists formats supported in 4:2:0; Y420CMDB maps 4:2:0 capability to positions in the CTA Video Data Block.
The first byte of a CTA data block combines its tag and payload length. Extended-tag blocks use the first payload byte as an additional type code.
VESA DisplayID 2.1a
A flexible data-block framework
DisplayID describes physical and performance attributes through typed, variable-length data blocks. When DisplayID 2.0 structure is carried as an EDID extension, the extension tag is 70h.
version 20hWhat changes from EDID 1.4?
- Most information is carried in reusable data blocks.
- A three-byte block header identifies tag, revision/flags, and payload length.
- Mandatory blocks and ordering depend on how the structure is used.
- At least one timing is identified and one timing is declared preferred.
- Fixed-length 128-byte mapping is defined for use as EDID extensions.
20h / 21hProduct & display parameters
Identity, product naming, image size, native format, feature support, chromaticity, luminance, depth, technology, and gamma-related information.
22hType VII timing
A detailed timing representation that explicitly carries timing parameters and preferred-mode information.
23hType VIII timing
An enumerated timing-code representation for formats defined by a referenced timing standard.
24h / 2AhType IX & X formula timings
Formula-based modes; Type X was added to support multiple CVT 2.1 Reduced Blanking v3 timings.
26h–2BhAdvanced capabilities
Interface features, stereo, tiled topology, ContainerID, Adaptive-Sync, and related modern display information.
Integrity & meaning
Validation happens in layers
A checksum is necessary, but it only proves arithmetic consistency. A strong validator also checks layout, legal values, and relationships between fields.
- 1Container
Length is a whole number of 128-byte blocks and stays within implementation limits.
- 2Block integrity
Base header is present, every block checksum passes, and extension count matches actual blocks.
- 3Field structure
Offsets, lengths, descriptor envelopes, reserved values, and data-block boundaries are legal.
- 4Cross-field meaning
Preferred/native flags, timing ranges, color formats, maps, and dependent fields agree.
- 5System test
The source, transport path, and sink reliably operate with the advertised format.
Fast structural checklist
Three costly assumptions
“The checksum passes, so the EDID is correct.”
No. A perfectly checksummed block can contain contradictory, reserved, or physically impossible data.
“Preferred” and “native” always mean the same thing.
No. They are related concepts with context-specific signaling. CTA native SVDs and native DTD count are separate from the EDID 1.4 preferred timing.
More advertised modes are always better.
No. Extra modes can change source selection behavior and expose combinations the end-to-end path cannot carry reliably.
Apply it in EdidCraft
A safe decode–edit–validate loop
Keep the original, change one capability domain at a time, and verify both the generated bytes and the real signal path.
Inspect identity, timings, extensions, and raw blocks.
Separate pre-existing issues from your changes.
Transfer the decoded draft and change only what is intended.
Decode the result again, compare, then test hardware.
Bridge fidelity report
What “Preserved unchanged” means
EdidCraft maps standards-safe fields into editable controls. Blocks without a complete semantic editor—often HDMI vendor data or some extension timings—are carried forward as validated raw bytes.
- Imported
- Editable in the Encoder
- Preserved
- Retained losslessly, not editable
- Review
- Valid transfer with a warning or contextual risk
- Not imported
- Source bytes were unavailable; abnormal for a normal bridge request
Reference
Glossary & quick answers
The vocabulary that appears most often in decoders, datasheets, and standards.
EDID
Extended Display Identification Data: display capability data read by a source.
E-EDID
The enhanced framework that includes the base EDID plus extension blocks.
DDC
The communication channel commonly used to retrieve EDID over HDMI/DVI-style connections.
DTD
An explicit 18-byte timing descriptor containing the waveform parameters for one mode.
VIC
A CTA-defined numeric identifier for a standardized video format.
SVD
A compact CTA Video Data Block entry that advertises a VIC and native status where defined.
SAD
A three-byte CTA audio capability record.
VSDB
A CTA block whose interpretation is owned by the organization identified in its payload.
OUI
An IEEE organizational identifier used to identify the owner of vendor-defined data.
DMT
VESA’s catalog of defined display monitor timing modes.
CVT
VESA’s equation-based method for generating coordinated video timings.
RB
Reduced Blanking: CVT timing families intended to reduce blanking overhead for non-CRT displays.
EOTF
The mapping from an electrical signal value to displayed light output; signaled by HDR capability data.
YCbCr 4:2:0
A chroma-subsampled encoding with lower chroma data rate than 4:4:4.
Frequently asked questions
Can an EDID force a source to output one mode?
It can strongly influence selection by advertising and prioritizing modes, but source policy, operating system settings, driver behavior, and link constraints still decide the actual output.
Why is my EDID 256 bytes instead of 128?
It contains the 128-byte base block plus one 128-byte extension. CTA-861 is the most common extension in HDMI-oriented systems.
Should I delete blocks my editor does not understand?
Usually no. Vendor and unimplemented blocks may carry essential link capabilities. Preserve them unless you understand their governing specification and intend to replace them.
Why do 59.94 Hz and 60 Hz both appear?
They belong to different frame-rate families and may use different exact clocks. A rounded UI label is not enough to prove two timings are identical.
Does recalculating the checksum repair a broken EDID?
It repairs only the checksum byte. Invalid lengths, reserved values, contradictory capability claims, and incorrect timings remain incorrect.
Local reference set
Standards used for this guide
ANSI/CTA-861-H
CTA extension layout, video formats, data blocks, audio, colorimetry, HDR, and YCbCr 4:2:0 signaling.
E-EDID Verification Guide, Release A
EDID 1.4 base-block field layout, descriptor rules, checksums, and verification test cases.
DisplayID 2.1a + errata
DisplayID sections, data-block headers, timing blocks, interfaces, tiled displays, and modern capability structures.
CVT 2.1
Equation-based standard and Reduced Blanking timing generation methods.
DMT 1.0, Revision 13
The bundled catalog of VESA and industry display monitor timing definitions.
This educational summary is not a conformance specification. If it conflicts with a normative standard, the normative standard controls.
Put the model to work
Decode a real EDID while the byte map is fresh
Start with an original file, inspect its structure, then validate it before making changes.