Disclaimer:- All the information I’ve put here is based on my own research or experience. As always, if you find inaccuracies or problems with the information here do let me know in the comments or by using the contact page.
HDMI is the modern, all digital replacement for SCART, analogue component video and other analogue cables and connectors. HDMI is now ubiquitous on consumer television sets and is found on many computer monitors too. The HDMI standard was designed by a consortium of hardware manufacturers and (unfortunately, as we’ll discuss later), content providers. It offers many advantages over the old analogue video standards, but unfortunately several disadvantages too.
One cable – Perfect picture and sound every time
HDMI is a digitally lossless form of transmitting audio and video. In the old analogue world, signals were affected by interference, cable quality and lots of other factors. By moving to digital, these factors have been eliminated. Of course, there’s still the high-street stores, audiophile magazines and other snake-oil salesmen that will insist that you need an expensive cable to “get the most out of your setup”, this has been thoroughly dis-proven by Digital Foundry in their article. If your HDMI cable is faulty or not performing properly, you’ll either see your picture blank out entirely for a second or more, or see strange, sparkle like patterns on your screen. In the absence of these anomalies, you can rest assured you’re getting the best quality possible down the cable.
Carries audio too
One of the other problems with analogue audio was the amount of cables that needed to be run. Three cables for component video, then how about seven more for your surround sound? By moving to optical audio this could be reduced to one, but only if you were happy with 5.1 dolby digital. HDMI cables have enough bandwidth for uncompressed, 7.1 audio, meaning you won’t need to trail seven big, thick RCA cables across your room even if you have the fanciest of setups. Just like the picture, sound is digitally encoded too, ensuring you always get the best quality down the cable.
There have been several revisions to the basic HDMI standard, each new revision brought new features such as support for Dolby True HD streaming or ethernet over HDMI. The HDMI article on Wikipedia lists all the different revisions and what changes and improvements they included. Originally each version of HDMI was given a version number, but the HDMI consortium decided recently that this was too confusing. If you want to make sure that your cables are compatible, look for either HDMI 1.4 (or later) or HDMI high speed branded cables. Since no games console supports ethernet over HDMI, it’s not necessary to buy a cable with this feature. Cables that aren’t rated for high speed are still compatible up to 1080i, but HDMI high speed cables can be bought very cheaply online, so there’s little point trying to save a few cents/pence just because you normally run your Xbox 360 in 720p.
So far, it seems like HDMI is pretty great, we get perfect picture and sound without worrying too much about cable quality. Sadly, it’s not all good news.
Because HDMI was designed in collaboration with big content companies like Fox, Disney and Warner Brothers, it was inevitable that some kind of copy protection was written into the standard. HDCP, which is an acronym for High Definition Content Protection, is an end to end encryption standard that makes it impossible to record or capture protected streams. Apart from making older DVI only displays obsolete overnight, HDCP creates a number of problems for the videophile and videogamer too. Capturing your gameplay from the PS3 is particularly difficult due to HDCP being turned on permanently. Allegedly several of the content companies pushed for the copy protection to be mandatory on all streams, but in the final standard this isn’t the case. The HDMI streams from the Xbox 360, PC and Wii-U are all unencrypted unless you are watching a movie. Only the PS3, for reasons known only to Sony, has HDCP encryption turned on during gameplay.
Like most copy protection schemes, HDCP has been broken and it is possible to buy HDCP strippers that will remove the copy protection from the signal. As you might imagine, however, it’s not usually possible to pick them up at your local electronics store, as modern copyright law makes selling such devices in many countries illegal.
In the days of analogue TV and connections, you turned on your TV, turned it over to the RGB or S-Video or whatever input, turned on your games console and got a picture instantly. As long as cables were correctly inserted, there were no problems with audio not playing, or pictures not being displayed. With HDMI, the digital protocols need to establish a connection between the sending and receiving devices. This process is called handshaking. During this process the two bits of AV gear exchange a piece of information called an EDID. This information tells each device what the capabilities of the other device are, so, for instance, if your TV isn’t 3D compatible, the blu-ray player you just hooked up knows it cannot output 3D content. That’s the theory anyway, though there are a few problems in practice. One is that, when the signal changes, the handshake has to be re-negotiated. Typically you can see this on video processors like the XRGB Mini. When a game changes between interlace (480i or 576i) and progressive (240p or 288p) there’s a long pause as the handshake is renegotiated. This delay, of course, didn’t affect the analogue CRT displays of the time and so older software doesn’t account for it. This can render some older games unplayable on modern TV’s, even with a suitable, 240p/288p aware video-processor device.
The other problem with handshaking relates to the EDID specifically. EDID’s supposedly make consumer electronics more ‘intelligent’. That’s fine if you can override this intelligence when it inevitably turns into stupidity, but unfortunately that’s not always the case. The biggest offender here is the PC. Windows uses the EDID to determine what kind of audio signal it can output through the HDMI cable. In many cases this is read incorrectly, especially if, for instance, you have your PC’s HDMI or DVI output split between your monitor for work and your television for gaming. In this instance, Windows will refuse to output surround sound, even though you know your receiver is more than capable of doing so. One way to fix this problem is to use a Dr HDMI unit, which we reviewed over on this page.
It’s not uncommon for handshaking to fail, in some systems you may need to switch equipment on in a certain order, or even power-cycle your TV or video processor/AV receiver from time to time to get the handshake to work properly.HDMI vs DVI
HDMI was designed to be backwards compatible with DVI. HDMI to DVI converters are bi-directional and do not need to do any image processing or converting. Although the DVI standard didn’t originally include sound in its specification, DVI cables will still carry sound and most DVI splitters and switches will work perfectly fine when fed a HDMI signal that includes both audio and video information. Most modern DVI-equipped monitors can handle HDCP too. Of course, while DVI supports both analogue and digital connections for backwards compatibility with older PC monitors, HDMI does not.
Converting to and from HDMI
There are several ways to convert and upscale analogue video to HDMI, many of which we cover on this site. One of the oldest and best pages on the subject for videogamers can be found here.
If you need to convert from HDMI back into analogue, perhaps to use a CRT projector or to add scanlines to a 480p image, the HD Fury line of adapters can break the HDCP and move the digital video back into the analogue domain.
References and further reading