We are frequently asked, "can you make a cable that has three RCAs for component video on one end and an HDMI connector on the other?" The answer, unfortunately, is: "Yes, we can make it. And no, it will not work." Why?
The problem with making a component to HDMI cable is, simply, that HDMI and component video are two entirely different ways of representing a video image as a set of electrical signals. They do bear some similarities; both break the colors up into three streams of red, green and blue (though these, in a component video signal, are actually carried as luminance and "color difference" signals), and both run these three streams in parallel with one another to the display. But that's where the similarities end.
Component video is an analog format. What this means is that the values of the color signals are represented by continuously varying voltages, with, theoretically at least, a nearly infinite number of possible voltage values representing the complete range of colors. HDMI, on the other hand, is a digital format. Although the three HDMI cable twisted pairs that carry red, green and blue also carry signals representing the values of the red, green and blue components of the signal, these signals are not continuously variable, analog voltages. Rather, they are digital information--ones and zeros--sent by a digital transmitting circuit that rapidly alternates between a negative and a positive voltage. These ones and zeros have to be received by another digital circuit, interpreted, and transformed by that circuit into color intensities to be displayed on a screen.
The type of circuit that puts out or takes in an analog component video signal is completely unlike the sort of circuit that puts out or takes in a digital HDMI signal. It's not hard to physically hook the two up--all you need is a soldering iron, an HDMI cable, and a willingness for needless destruction (though, since an HDMI cable has nineteen contacts and a component cable only six, there'll be some spare wire left over)--but the two circuits have no idea how to talk to one another.
Ordinarily, the answer to this sort of problem is very simple. If both of your devices have HDMI connections available, hook them up with an HDMI cable; if both have component video, hook them up by component video cable; and if both have both, take your pick. If your only problem is that your devices support the video types, but you are short of input or output jacks, buy a switch. But now and then we do run into someone who really has a problematic situation, and needs to get HDMI to run into a component video input or vice versa. What's to be done?
There are such things as active converter circuits, which will take a signal of one type, process it, and convert it to a signal of the other type. We don't sell that sort of thing, but there are broadcast-supply houses online which do. Before you go shopping for one, though, there are a couple of points of which to take note. First, these devices typically are expensive, ranging anywhere from around $300 to a thousand dollars or more; it's often cheaper to replace your source or your display. Second, if you're converting HDMI to analog video, consider this: because of the restrictions imposed by the Digital Millennium Copyright Act (DMCA), it's very likely that any HDMI to analog converter box you find will have HDCP (High-Definition Content Protection) enabled, which means that you will not be able to view HDCP-protected sources through that converter. If you have to do it, you have to do it; but if you can avoid it, you'll also avoid some real potential headaches.
* An added note: we have, on rare occasion, seen devices which provide a nonstandard wiring setup where it is possible to route analog component video through an HDMI socket. These devices are extremely rare, and if you have one, your user's manual will clearly state as much. Unfortunately, because there are a few such devices on the market, there are now "HDMI to Component" cables being marketed in various outlets (we've seen them on Amazon and eBay), and the sellers of these products often do not appear to realize that they will work with only a very small, limited class of devices. Don't buy one just to try out; unless your manual says it will work, it WILL NOT.