Knowledge Base

The HDMI Licensing Knowledge Base is a library of current information about the HDMI standard. Select an appropriate category from the pull down below, or, you may use your own search terms to obtain results.

If your question involves a specific product, please contact the manufacturer directly. The HDMI Knowledge Base does not contain information about specific products.

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Compatibility and Interoperability

Q. Do I need v1.3 HDMI to hear the new Dolby TrueHD and DTS Master HD audio content on HD-DVD or Blu-ray players?

No. The Dolby TrueHD, Dolby Digital Plus, and DTS-HD Master Audio can be decoded by the playback device into multi-channel Pulse Code Modulation (PCM) digital audio streams, which is an audio format standard that can be sent over any version of HDMI. In fact, all versions of HDMI can support up to 8 channels of PCM audio at 192kHz, 24 bits per sample.

To do this, consumers should ensure that their playback device (such as HD-DVD or Blu-ray player) is capable of decoding these new lossless Dolby & DTS audio formats into the PCM format on the HDMI output, and that the audio device (such as an A/V receiver) is capable of receiving multi-channel PCM audio over the HDMI inputs. Consult your user manual/product specification sheet to determine whether your device supports such PCM capabilities (we believe that nearly all HD-DVD and Blu-ray players will, but users should confirm this). Devices that support HDMI v1.3 and higher may also offer the option to transport the high definition audio formats as a compressed, encoded stream over HDMI so that the decoding function can be performed by the A/V receiver (whereas the above transport method has the playback device performing the decoding).

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Q. What is the difference in quality between listening to Dolby TrueHD/DTS-HD over HDMI, SPDIF (i.e. coax or optical), or analog from the player to the A/V receiver?

HDMI provides the highest quality as it enables the full, lossless audio data of Dolby TrueHD to be transferred digitally to the AV receiver, and enables the A/V receiver to apply its full digital audio processing capabilities (such as bass management, or sound field processing effects) to further enhance the audio quality. S/PDIF does not have the ability to support the data rates required by Dolby TrueHD, and thus will not support it. Analog will be lower quality than HDMI due to two reasons: 1) the nature of analog transmission is lossy and will degrade while transported over the cables, 2) many A/V receivers will not apply any digital audio processing to the analog inputs, and in such cases analog signals will be sent directly to the amplifier without the benefit of such processing.

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Q. What is the difference between decoding Dolby TrueHD/DTS-HD in the player (i.e. sending over HDMI as decoded PCM) vs. decoding in the A/V receiver (i.e. sending over HDMI as encoded Dolby TrueHD/DTS-HD bitstream)?

There is no inherent difference in quality between Dolby TrueHD/DTS-HD being sent over HDMI as decoded PCM vs. encoded bit stream. All Dolby TrueHD/DTS-HD decoders (whether in the player or the A/V receiver) must be certified to meet stringent quality requirements. However, consumers should make sure that their receivers support the number of incoming PCM channels delivered by their source device (e.g. DVD).

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Q. Why is Lip Sync important?

In a DTV, typically the video processing takes more time than the audio. As a result, lip sync can become an issue where it is noticeable to the viewer, creating an effect similar to that of a badly-dubbed movie. HDMI 1.3 provides a method whereby the audio processing times in devices can be automatically adjusted to remove lip sync errors.

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Q. Is HDMI backward compatible with DVI (Digital Visual Interface)?

Yes, HDMI is fully backward compatible with DVI compliant devices. HDMI DTVs will display video received from existing DVI-equipped products, and DVI-equipped TVs will display video from HDMI sources. However, some older PCs with DVI are designed only to support computer monitors, not televisions. Consumers buying a PC with DVI should make sure that it specifically includes support for television formats and not just computer monitors.

Also, consumers may want to confirm that the DVI interface supports High-bandwidth Digital Content Protection (HDCP), as content that requires HDCP copy protection will require that both the HDMI and DVI devices support HDCP to properly view the video content.

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Q. What version of HDMI does a consumer need to view 1080p content?

HDMI has always supported 1080p resolution, starting from version 1.0 in 2002. However, as with many functions that HDMI enables (such as DVD-Audio and SACD), it is up to the manufacturer to choose whether to implement 1080p in the device. Some TV and device manufacturers have chosen not to implement 1080p in their products because 1080p content has not been widely available, and because changing the internal electronics of the device to support 1080p would increase cost.

Viewing 1080p resolution requires at minimum that the HDTV have a display supporting the 1080p pixel resolution. Today, many HDTVs use display technologies (such as PDP, LCD, and microdisplay screens) designed for 720p pixel resolution. In the past, some 1080p HDTVs supported only 720p or 1080i on the HDMI input, then perform video processing to up-convert the 720p/1080i signal to 1080p. This is now changing, as 1080p content is becoming increasingly available, and HDTVs fully supporting 1080p in the display and HDMI electronics became more popular in the market in early 2006. True 1080p HDTVs are currently offered in the market by a variety of TV manufacturers.

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Q. Do you need a new version of HDMI to play Blu-ray and HD-DVD content in high definition?

All versions of the HDMI specification support the ability to watch HD-DVD / Blu-ray content in high definition up to 1080p resolution. However, there may be non-HDMI reasons that prevent some devices from accessing content in high definition, including lack of HDCP support.

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Q. Does HDMI support Dolby 5.1 audio and high-resolution audio formats?

Yes. From the start, HDMI was defined to carry 8-channels, of 192kHz, 24-bit uncompressed audio, which exceeds all current consumer media formats. In addition, HDMI can carry any flavor of compressed audio format such as Dolby or DTS. (Such compressed formats are the only multi-channel or high-resolution audio formats that can be carried across the older S/PDIF or AES/EBU interfaces.) Additionally, most existing HDMI sources can output any compressed stream, and the newer sources can output uncompressed 6-channel, 96kHz audio from a DVD-Audio disk. There are A/V receivers on the market that can accept and process the 6- or 8-channel audio from HDMI.

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Q. Does HDMI support Dolby Digital, DTS, and high-resolution audio formats?

Yes. From the start, HDMI was defined to carry 8-channels of 192kHz, 24-bit uncompressed audio, which exceeds all current consumer media formats. In addition, HDMI can carry any currently available flavor of compressed audio format such as Dolby (including Dolby Digital EX 7.1, Dolby Digital Plus 7.1, Dolby TrueHD) or DTS (including DTS-ES 6.1 and DTS-HD Master Audio). Such compressed formats are the only multi-channel or high-resolution audio formats that can be carried across the older S/PDIF or AES/EBU interfaces. HDMI 1.3 adds additional support for new lossless digital surround audio formats Dolby TrueHD and DTS-HD Master Audio. Additionally, most existing HDMI sources can output any compressed stream, and the newer sources can output uncompressed 6-channel, 96kHz audio from a DVD-Audio disk. There are A/V receivers on the market that can accept and process the 6- or 8-channel audio over HDMI.

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Q. Does HDMI support SACD?

HDMI has supported One Bit Audio format, such as SuperAudio CD's DSD (Direct Stream Digital), since version 1.2 (released in August, 2005). Customers interested in this feature should make sure that their device supports SACD.

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Q. What is the most common compatibility problem among devices with HDMI connections?

The most common compatibility problems have to do with HDCP. Probably the most common failure is the lack of an HDCP repeater function or failure to perform the authentication reliably in all types of usage scenarios. We are increasingly seeing HDCP becoming less and less of a problem as manufacturers iron out the kinks in later generation devices and as cable operators download upgraded firmware to their set-top boxes. In addition, as of November, 2006, the HDMI Founders required all HDMI devices implementing HDCP to undergo a new mandatory compliance testing program of the HDCP functions. This is based on the HDCP Compliance Test Specification.

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Q. Some cable TV set-top boxes with HDMI outputs don’t deliver a picture to displays with HDMI inputs. What is the problem, and is there a solution?

In some cases, the set-top box software does not activate or support the HDMI port. In other cases, cable TV set-top boxes don’t work correctly when used in conjunction with an A/V receiver (but will typically function correctly when connected directly to a TV or monitor). Investigation of some of these devices reveals that this is caused by an error in the way these set-top box devices implement HDCP. Specifically, some of those boxes do not support "HDCP repeaters" (devices that pass along the signal to another device) such as an A/V receiver or switch. We believe that this may be a problem in the initial versions of these products, and in some cases there is new firmware available that fixes this issue in HDMI (newer versions may already have this fix). We have been actively working with manufacturers to resolve these problems. We suggest that users contact their cable operator and request the new software to address these issues. As noted above, cable operators are increasingly downloading the available firmware upgrades required to fix this error.

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Q. If an HDMI accessory device (i.e. switch box, cable booster) does not have a dedicated power supply, is it still compliant and will it work?

An HDMI device that has active electronics should have a provision for external power in order to be compliant (e.g. a receptacle to allow the use of a standard power adapter, sometimes called a power “brick”). Here we are drawing a distinction between “active” devices that actually have some powered electronics, and “passive” devices, such as some switches (more on those later).

Some active devices, such as actively powered HDMI cables or in-line signal extender boxes, will by default attempt to power their electronics by taking power from the 5V line (+5V power) available on the HDMI connector. The HDMI specification requires all source devices to provide at least 55mA (milliamps) on the 5V line for the purpose of reading the EDID of a display. While 55mA is not enough current to operate most HDMI accessory devices (which typically require about 100 to 150mA), most source devices on the market today provide significantly more current on the 5V line than the HDMI specification requires. As a result, the vast majority of accessory devices can operate when interfaced with a source device that provides more than the required current (i.e. over 100-150mA) on the 5V line. However, manufacturers should provide a provision for their powered HDMI accessory devices to obtain external power, and consumers are encouraged to look for this external power provision when purchasing such products.

Looking to the future, not all HDMI devices may provide this much power over the 5V line. For example, as HDMI expands into more and more portable applications (cameras, camcorders, laptops, etc.), power consumption is often much more of an issue, and such devices may not power the 5V line with the > 100mA required by such “active” devices. Again, consumers should consider ensuring that their active HDMI accessory device purchases have a provision for external power for this reason.

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Q. Can any passive devices that use no active electronics (such as a mechanical switch box) be compliant?

Any device which performs processing, amplification, or switching of the HDMI signal should use actively powered electronics to be compliant and perform reliably. As mentioned in the above question, the vast majority of devices can utilize power that is supplied on the 5V line (+5V power) of the HDMI connector to function properly, although we recommend that such devices give the users an optional provision to use an external power adapter. Completely passive, non-powered devices may work in some short-cable length applications, but use them at your own risk, as they may not operate reliably. Even if a passive device works in one configuration, a change in equipment or cabling may introduce failures in subsequent configurations.

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Q. Can HDMI cables contribute to devices not working properly together?

The vast majority of image quality or interoperability issues with HDMI devices are related to the software (firmware) used for device communication and content protection, and have nothing to do with the HDMI cable. In particular, these issues are often caused by the software related to HDCP handshaking, or from devices improperly handling the device capability information read through HDMI (e.g. the device has an incorrect EDID, or an inability to properly read an EDID). It is fairly uncommon for the cable to be the cause of HDMI compatibility problems. In fact, the robustness of the HDMI specification has been verified by the fact that we have not found a compliant HDMI cable that is the root cause of HDMI playback issues with compliant devices.

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Q. If my digital monitor doesn’t have an HDCP-compatible connection (such as an HDMI connection with HDCP), will I be able to view HD DVD and Blu-ray content in high definition?

Content owners (i.e., a movie studio releasing a DVD) decide which technologies they will use to protect their content against unauthorized copying. Movie studios, that fear that high-definition versions of their movies will be pirated, are expected to use HDCP when releasing high-definition versions of their movies, though some may choose to release some titles without HDCP. To be safe, consumers who want to be able to play high-definition content should ensure that their HDTVs and other HD devices are able to decode HDCP-encrypted content.

There are also specific requirements on HDCP usage mandated by the U.S. Federal Communications Commission and by industry bodies in Europe and Asia. See below for more information.

With certain exceptions, nearly all HDMI devices on the market include HDCP support. DVI devices, in particular earlier versions of DVI, are more likely to lack HDCP support.

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Q. Are there DVI to HDMI Cables/Converters?

HDMI is backward compatiable with DVI. You will not receive any sound by using DVI, but the picture quality should be excellent. There are a number of different systems and cables iut there, and Gefen makes a very popular one.

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Q. What if I want to convert Dvi to HDMI (or other signals…?

There are many converts on the market. Check out Gefen

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Q. Can I upgrade my existing HDMI equipment to add the newer features?

Currently, there are no provisions for doing such an upgrade. Because of the new enhanced feature set, any such conversion would require hardware and firmware upgrades. If there are such conversions, it would come from the manufacturer. Please check with them directly.

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Q. Can I download future versions of HDMI?

No. HDMI upgrades usually require changes in hardware and firmware. For this reason, HDMI would be difficult to upgrade from a computer.

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Q. What is the cost of upgrading a PC system from DVI to HDMI?

There are several options. The lowest cost would be to add a basic PCI Express HDMI Graphics card for approximately US$100. Higher end graphics cards, however, can offer better performance in certain applications. For example, for around $US400, manufacturers are offering a high-end graphics card with built-in processing power so that as the user watches a movie, for example, he or she can also use the processing power of the computer to do other work. The processor on the graphics card is doing the required processing to play the movie, leaving the PC’s CPU free to perform other applications. As well, some graphics cards have their own audio controller and do not require an external S/PDIF input.

If you intend to use your PC to render video on a large TV, make sure your HDMI graphics cards incorporates high-quality video processing. ATI Avivo™ or nVIDIA’s PureVideo™ HD2 technology are two such offerings from these companies.

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Q. What can a PC with HDMI do that cannot be done with DVI?

HDMI offers both audio and video over one single cable making set-up and cabling much simpler. With this convergence interface, HDMI offers a simple way for PCs to connect to a TV.

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Q. What is the difference between EDID and E-EDID?

EDID was formed as a standard to help PC monitors report their capabilities. E-EDID is an extension of the EDID specification used traditionally by consumer electronic devices to illustrate more advanced features.

For example, PC monitors generally do not support audio, so a traditional EDID structure would not account for this, whereas an E-EDID would.

The requirements for a consumer electronics device’s E-EDID are available in the CEA- 861B specification (

The requirements for a PC device EDID are available from VESA (

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