What is HDMI?
See Wikipedia for a full definition, but it is essentially a way to plug your high definition video sources into your display device. Decoded: plug your HD-DVD to your TV.
Is it Better?
HDMI touts several advantages over the existing alternative, Component Video. It is digital instead of analog, carries audio as well as video, and does it all in a single cable. These all sound great, but are they really true?
Digital v. Analog - Both Component and HDMI are capable of carrying signals up to 1080p. There are no obvious performance differences, and an unscientific analysis from people who have tested both have produced mixed results. The bottom line, no clear advantage.
Easier - No doubt, HDMI is easier to plug in than Component cables and digital audio cables. Of course, most people do this once a year at most, so I'm not sure this should carry much weight.
Not only are HDMI's advantages minimal, but it has some purely technical disadvantages as well.
Short Runs - HDMI's max length is generally stated to be about 50', although this can only be achieved with high quality cables. This is great if you are plugging your DVD player into your TV in the same entertainment center, but when you start talking about home theaters with projectors or hooking up your second TV, there are major issues. Component cables can be run much longer (100' or more). (I'm a fan of Blue Jean Cable, and you can see their thoughts about why HDMI is broken)
Incompatibility - There are many reports about sources and display devices having computability problems. One 'feature' of HDMI is that is uses HDCP to protect the content. This means that the two sources exchange keys and then use those keys to encrypt all data transmitted. When this works fine it is seamless. However, many people have reported issues with the signal dropping, causing them to have to 'reboot' their source and/or display.
This issue really hit home for me recently as I started investigating a way to do 'whole house' distribution of my High Definition DVR. I currently do whole house distribution of Standard Definition signals using an RF Modulator (topic for a future post). However, as I now have a second High Definition television, I'd like to be able to watch my DVR'ed shows on either TV.
What I've found is that while there are a ton of ways to distribute component video signals using Cat5 cable, there is no way to convert HDMI or DVI sources to Component. Additionally, there are no ways to distribute HDMI over long distances.
The issue lies with Digital Rights Management (DRM). It is illegal (in the US at least) to sell equipment that will convert HDMI or DVI signals to component (or any other analog) signal. This is part of what is known as 'closing the analog hole'.
So why does this matter? After all, most sources can output their signal on either Component or HDMI right? Well, sort of. My existing source (High Def DirecTivo) will output its signal in full definition on any output. However, many new devices will not allow the full signal on Component cables.
Upconverting DVDs - Most (all?) current Upconverting DVD players will only output full High Def (1080i) on the HDMI inputs. The Component outputs will only output up to 480p. See the OPPO DV 970HD as an example. I have found some that have work arounds, etc, but by and large the component outputs are already locked out.
XBox 360 - While it does appear that you can output High Def on the component output (it does not even have HDMI), there are a few catches. Basically, it won't upconvert DVDs on the Component output (only on the VGA output), and it will downconvert HD-DVD to 1080i (from 1080p) on component, although full 1080p will be available on VGA. This seems odd as the VGA output should be unprotected.
Regardless, the bottom line is that studios and manufacturers are locking down and limiting the capabilities of the Component outputs, and while there are some work arounds today, these will continue to be harder to find and implement.
In the future, it may become impossible to distribute High Definition signals to multiple TVs in your home.