WHAT IS EDID AND WHY IS IT IMPORTANT?This question comes up a lot when troubleshooting unusual video capture issues with customers.
Usual basic description is that EDID is the information provided by a monitor to the video source describing the monitor’s capabilities. This allows the video source to then send out a video signal that is supported by the monitor. EDIDs are important for DVI and HDMI video sources and occasionally used for VGA sources.
What is EDID?
EDID is an acronym for “Extended Display Identification Data”. This short set of letters can be the source of a major headache when it comes to HDMI.
When establishing an HDMI connection, the source device must be able to communicate with the display (known as the Sink) and find out what capabilities it has. The communication between these two devices is what is known as the “HDMI handshake”.
During this process, the source is attempting to find out what the Sink’s maximum capabilities are so it can transmit the best possible signal.
Where is EDID Utilized?
Generally, the source device will be a computer graphics card on a desktop or laptop PC, but provisions are in place for many other devices, including HDTV receivers and DVRs, DVD and Blu-ray Disc players, and even gaming consoles, to read EDID and output video accordingly. Originally developed for use between analog computer-video devices with VGA ports, EDID is also now implemented for DVI, HDMI, and DisplayPort.
History
EDID was developed by VESA - the Video Electronics Standards Association, with version 1.0 introduced in 1994 within version 1.0 of the DDC standard.
Prior to the development of EDID, pins 4, 11, 12, and 15 on the VGA connector were sometimes used to define monitor capabilities. These ID bit pins carried either high or low values to define different screen resolutions. VESA extended this scheme by redefining VGA connector pins 9, 12, and 15 as a serial bus in the form of the DDC - Display Data Channel. This allowed for much more information to be exchanged, so that EDID and other forms of communication were possible between the source and the display.
The original DDC protocol defined 128 bytes to be sent from the display to the video source, with data formatting defined by the EDID specification.
As display types and capabilities increased, 128 bytes became insufficient, and both EDID and DDC were extended so that multiple 128-byte data blocks could be exchanged. This is known as E-EDID and has been implemented in many consumer devices. In fact, the CEA - Consumer Electronics Association has defined its own EDID extensions to cover additional video formats and to support advanced multi-channel audio capabilities.
In December 2007, VESA released DisplayID, a second generation of EDID. It is intended to replace all previous versions. DisplayID is a variable length data structure, of up to 256 bytes, that conveys display-related information to attached source devices. It is meant to encompass PC display devices, consumer televisions, and embedded displays such as LCD screens within laptops, without the need for multiple extension blocks. DisplayID is not directly backward compatible with previous EDID/E-EDID versions, but is not yet widely incorporated in AV products.
Extended Display Identification Data is a VESA standard data format that contains basic information about a monitor and its capabilities, including vendor information, maximum image size, color characteristics, factory pre-set timings, frequency range limits, and character strings for the monitor name and serial number.
The information is stored in the display and is used to communicate with the system through a Display Data Channel (DDC ), which sites between the monitor and the PC graphics adapter. The system uses this information for configurationpurposes, so the monitor and system can work together.
The latest version of EDID (version 1.3) can be used in CRT displays, LCD displays, and future display types because EDID offers general descriptions of almost all display parameters.
Types of information that might be communicated include:
EDID version
Manufacturer ID
Model Number
Serial Number
Video Resolutions
Video Timing Bitmaps and Descriptors
Chromaticity Coordinates
Video Field Rates
White Point Descriptors
Display Power Management Info
Vendor/Product Identification Block – The first 18 bytes identify the display manufacturer and product, including serial number and date of manufacture.
EDID Structure Version & Revision – The next two bytes identify the version and revision of the EDID data within the structure.
Basic Display Parameters/Features – The next five bytes define characteristics such as whether the display accepts analog or digital inputs, sync types, maximum horizontal and vertical size of the display, gamma transfer characteristics, power management capabilities, color space, and default video timing.
Color Characteristics – The next 10 bytes define the RGB color space conversion technique to be used by the display.
Established Timings – The next three bytes define the VESA-established video resolutions/timings that are supported by the display. Each bit represents an established timing such as 640x480/60. The last of the three bytes defines the manufacturer's reserved timing, if any.
Standard Timing Identification – The next 16 bytes define eight additional video resolutions supported by the display. These resolutions must adhere to standard VESA defined timings.
Detailed Timing Descriptions – The next 72 bytes are organized into four 18-byte blocks that describe additional video resolutions in detail, so that custom video timings/resolutions can be supported. The first of the four blocks is intended to describe the display's preferred video timing. The timing data can be structured according to the VESA GTF - Generalized Timing Formula or CVT - Coordinated Video Timings standards.
Extension Flag – EDID versions 1.3 and higher allow for additional 128-byte blocks of data to describe increased capabilities.
This byte indicates the number of additional extension blocks available. Various structures for these extension blocks have been defined, including DI-EXT - Display Information Extension, VTB-EXT - Video Timing Block Extension, and LS-EXT - Localized String Extension.
CEA-861 Extension – The most prevalent EDID extension is CEA-861, defined to support advanced capabilities of consumer devices incorporating HDMI.
E-EDID
Here is another acronym for you. E-EDID stands for Enhanced EDID. This allows the devices to handle additional data, including vendor-specific specifications, as it opens up the data strings to 32 Kilobytes.
It’s just another way for your electronics to get a conversation going, but with a little more information.
Why so sad?
On the surface, this seems like it should be a simple process, right?
Not so fast. As long as you are connecting a single source to a single display, it’s usually smooth sailing.
However, throw in another device like a switch, extender or a splitter and chances are your devices might stop talking to one another. On occasion, the source device might have its EDID ROM coded incorrectly, which will cause issues from the outset.
In these cases, you might have trouble reaching the correct resolution or color issues. It might just fail to produce audio and/or video all together.
Of course if you really get into it, EDID, which stands for Extended Display Identification Data, is far more complicated. It includes vendor and product id, serial number, manufacture date, size of the display, resolution and frequencies supported, and detailed signal timings for native resolutions. Plus, often when we speak of EDID we are actually referring to E-EDID, or Enhanced Extended Display Identification Data.
When EDID was first introduced in 1994 it was short and sweet at just 128 bytes. It had vendor and product information, EDID revision, display capabilities (size, resolution, sync, etc), colour space, and detailed resolution/timing information. In 2000, E-EDID expanded this, allowing multiple 128 byte chunks. Today’s HDMI devices most often use E-EDID and include information to also specify audio capabilities including codecs, sampling rates, and channels.
I’m not going to get too low level or technical here, as this information is already available online and is just a quick Google search away. However I do want to address the practical concerns of EDIDs when using actual products.
When you connect your video source (e.g. camera, laptop, scientific instrument, etc) to any capture (or capture and streaming) device, our device acts as the “monitor” for your video source.
When would you use a custom EDID?
Here are a few reasons you may want to upload a specific EDID rather than using the default.
Resolution
Sometimes you want to try to force a video source to use a specific resolution. To do this you could upload an EDID that only lists that single video resolution. For example, we’ve found that on some laptops even though you tell the laptop to output video at 1080p, when it sees an EDID that has other resolutions, it picks one it likes better. Nothing you do from the OS can change the laptop’s mind. Uploading a custom EDID (with just one resolution) to the capture device can resolve the issue.
One important note, I did say “try” to force a video source. This is because even if the EDID lists only one specific resolution, interpreting this and sending out the right signal is still totally up to the video source and it is possible for the video source to ignore the EDID.
EDID Troubleshooting
The first step when you’re having issues you believe are related to EDID is to determine if it is the source device causing the issue.
Step 1
Connect the device directly to the TV with nothing in between to see if this solves the problem. If it does, then it’s the middle man causing issues.
Step 2
If it still fails to work, try connecting the source to a different TV that you know to be reliable. If this also fails, then your problem most likely lies with the source.
Step 3
Try updating the manufacturer firmware for whichever device you believe to be the troublemaker. This often takes care of the problems quickly and easily.
Step 4
Check the length of the cables you are using. The HDMI signal depends largely on the power of the device to which it is connected. Typically, HDMI can be transmitted up to 50 feet without issue, but some devices just don’t output enough power to make it past 30 feet or less (computers and gaming systems).
If the device isn’t producing enough power, the signal isn’t going to make it to its destination and the source will never get its EDID from the display. Splitters, switches, and of course, extenders, give that signal a boost to carry it further, but these also come with limitations. Check the device’s manual to ensure your cables are not too long for the run.
Step 5
Is your source a computer? Many TVs only accept specific computer resolutions. Make sure the resolution you are attempting to achieve is supported by your TV.
There are a number of different reasons your HDMI compliant devices might have trouble communicating, but hopefully this will get this you started if you’re experiencing issues! Remember, it may not always be the case that you’re working with defective devices. It could just be a missed communication.
The following are examples of some potential issues with EDID communications, along with the possible causes:
Problem
No image is shown on the display.
Possible Cause
The source device, such as a PC graphics card, or laptop, cannot read the EDID information from the display. As a result, in some cases the PC will not output any video signal.
Problem
The display loses the image when a new source has been selected.
Possible Cause
This is a common occurrence with VGA sources, due to the lack of hot plug detection.
While hot plug detection is supported for DVI, HDMI, and DisplayPort, EDID communication problems can arise from inconsistencies in the implementation of HPD signaling between devices from different manufacturers. This frequently becomes an issue for professional integration, since the ability to switch digital video signals is a necessity.
Problem
An image is shown, but the source resolution does not match that of the display.
Possible Cause
A PC cannot read the EDID information, so it defaults to a standard resolution, such as 640x480. If the user subsequently attempts to manually set the resolution to match the display, some graphics card drivers may enforce the lower default resolution and create a scrolling/panning desktop without actually changing the video resolution.
The PC is able to read the EDID information, but the graphics card limits the output resolution to XGA 1024x768, a resolution most displays can accommodate, ensuring a usable image and reducing the likelihood of no image being displayed. If this does not match the native resolution of the display, fonts will likely appear to be abnormally large, small, or fuzzy.
The PC is connected to multiple displays with different native resolutions. Since it can only read EDID from one display, the output will be mismatched in resolution with all other displays, resulting in less than optimal image quality, or no image displayed at all. This issue is a common occurrence in professional systems when video signals need to be distributed or routed to multiple displays.
