As if it's not bad enough with all this HDMI "stuff" that potential purchasers also have to worry about long HDMI Kabel runs. In the days of analog video the reliability of signal transmission over long kabel lengths never was a problem but in the first days of HDMI and DVI we heard rumors of consumers encountering problems over relatively short runs but everything has improved over time however the actual length you are able to run long HDMI Kabels over continues to be an industry hot potato.
Let's look at the latest HDMI specification to have an answer to the question. Every kabel has to be tested by the HDMI authorized test centers before they are able to gain compliance certification. These certificates can be used as some kind of unofficial guide for workable kabel lengths. There are a variety of kabel that are compliant at lengths over 10 meters there are some that have passed the testing up to 13.0 meters, so they are proven not to degrade the signal beyond a place stipulated by the accreditors. A great piece of advice is to buy certified kabel using the latest specification, at the moment HDMI is at 1.3b, but 1.3 and 1.3a are also acceptable, as the test protocols these kabel have to pass to receive the standard are more stringent compared to prior specification, say 1.1 or 1.2.
Prior to being tempted to buy anything over 13.0 meters (45-foot), they are available and being marketed as compliant, then it may be wise to ask to determine a copy of the certification because only at that present time the size of 13.0 meters (45-foot) is the longest none boosted (amplified) kabel that I have seen with the correct certification.
That said, there are available HDMI Kabels that are classed as active designed to use powered amplifiers to enhance the signal enabling longer runs of kabel to be used. An EQ unit is also used on these active kabel which looks at lost high frequency data after which compensates for this. These systems do work, but with no straight answers concerning actual effective length, the additional costs involved and the extra possibility of signal delivery failure in the inclusion of extra components it might be a step to far for your house entertainment system and best left to commercial applications.
But stop worrying if you need to run longer lengths of kabel. Just bear in mind the HDMI spec is the so you can be confident that whenever you build your system the compliant signal (source) can be connected to a compliant unit which can then be connected to a different using compliant kabel so when you switch everything onto it will work. As with all specification, inside will be built some leeway - over engineered - and so the source signal sent to the HD enabled equipment is better than is needed for your equipment to function as mentioned. This gives you a handful of options, options that don't fit into the specification so are not guaranteed to are in the example above, but options that have been proven to work and don't have the added costs of amplification.
There are connectors available which, although not compliant, will do employment and of course there are the over length (for compliance) kabel. If you're to go this way it's worth bearing in mind that the higher the bit rate your HD enabled devices are pulling the less possibility of success you have. You also need to remember that this also applies to long chains, HDTV to Blu-ray or home entertainment connected to the internet streaming video on demand at 1080p will be pushing longer kabel lengths, those over a compliant length, to it's limits. However for 480p, 720p or 1080i they may work fine. Would you see just how like guesswork this can be.
Now consider future advances, that you should if you are putting these kabel in walls etc., as if you are running on the limits of the kabel this could stop you upgrading. Take where we're at present. 1080p is the latest resolution for HDTV. Not that long ago 480p was the norm, then came 720p and 1080i which utilizes a bit rate almost 3 times that of standard 480p. Then along came 1080p that doubles the bit rate consumption of 1080i and 720p. Now we stand on the edge of 3d tv, 16 bit color and 1460p (and above), 16 bit color alone will double the required bit rate for current standard resolutions, this is why where this could go. One more important point to consider when deciding whether to go long or otherwise. It is a fact that on short kabel, those of 2-3 meter (6-10-foot) length, the quality matters less. A kabel costing a few dollars will perform just as good as one costing tens of dollars, but when entering the realms of none compliance quality matters far more. Generally speaking, the lower quality the kabel will be the lower the effective working distance will be when depth of color or picture resolution increases.
So lets unravel what's been said regarding long HDMI Kabels as well as their reliability. For the lengths that are HDMI compliant, those lengths up to about 13 meters (45-foot), their use is pretty much guaranteed, even if you're using the cheaper options, for 480p, 720p, 1080i and - even when not as consistently reliable - 1080p so go ahead and use them with confidence. The same thing goes for those shorter kabel of 1-3 meters (3-10-foot) lengths, though care should taken when utilizing them in long signal chains as they could become unreliable. Cheaper options from the longest HDMI compliant kabel working on the limits of it's performance capabilities may struggle in the 1460p, 16 bit color future as well as their use needs to be questioned if their installation is behind ceilings or walls as the additional cost of a far more expensive kabel may be less than a complete re-install in the (to not distant) future. The use of over compliant length HDMI Kabels needs to be linked to all the factors mentioned above but with the rider the best method of testing if it will be successful still lies with plugging it in. Even at these lengths, the cheaper choices are still worth considering when the installation of long HDMI Kabels is definitely accessed and they work Comfortable with your present equipment.