Especially popular for professional applications: the DVI interface, seen here with some products from Extron.

Video bitstream:
In the vast majority of cases, HDTV transmissions run from a source device to the screen - so the signals are already decompressed. Accessing the digital signal itself, the so-called bitstream, isn't easy - and, as a rule, you aren't supposed to access it. The reason for this is simple: The studios are afraid of unauthorized distribution.

If, however, a device is only designed to receive unencrypted TV, access to the bitstream is at least conceivable. In practice, however, this approach will often founder, since the appropriate connections (Ethernet or USB) can only be used as inputs. On the other hand, latest-generation HDTV satellite receivers are catching on to the concept of external storage - that is, on USB hard disks.

This allows the user to save the unchanged, transmitted data. Incidentally, it's almost never possible to stream live HD channels via Ethernet - the only exception is the dLan TV Sat from Devolo, which distributes the transmitted data throughout the house via the existing electricity cables.

DVI can be seen as the predecessor to HDMI, but is only rarely found in AV components. But some older TVs, projectors, and DVD players have the bulky-looking connection, which is actually compatible with HDMI. To connect it to HDMI, all you need is a simple adapter cable or a separate adapter.

DVI offers one advantage: the plug sits rock-solid in the socket, since it attaches to the casing with two screws. What's more, it'll even allow 1080p signals. The disadvantage: This type of connection (apart from on a few PC cards) cannot transmit sound. And even trickier than physically connecting the plug is often the signal compatibility, since early DVI interfaces lacked support for HDCP encryption - without HDCP, they won't even be able to carry video.

YUV - sometimes also known as YCbCr or YPbPr - is another connection that's suitable for transmitting HD video signals. Together with HDMI, this type of connection is compulsory for all devices carrying the "HD ready" logo.

As an analog cable, it is subject to different criteria from those that affect HDMI, since here the quality of the cable has a direct, visible effect on the picture. As an example, let's take a good CRT projector, without an HDMI input: This is going to need top-quality cables. Also very important in this case are solid and well-shielded plugs that fit the sockets perfectly.

There are no cables specifically for HDTV: after all, progressive scan in PAL resolution works at a considerable bandwidth. YUV counts as one of the more-robust types of connection - in practice, problems rarely occur. But we doubt whether this can make up for the connector's biggest disadvantage: YUV doesn't permit 1080p.

You can down-scale the video on the YUV outputs of Blu-ray players - pictured here is the BDP-LX91 from Pioneer.

High-resolution signals can originate from a computer, and you'll occasionally even find PC sockets on other devices - the first HDTV set-top box to hit the European market, for example, had a VGA output. And VGA can prove to be extremely useful for HD pictures, purely because - unlike YUV - it isn't limited to interlaced signals. Therefore, VGA sockets can also deliver accurate, analog 1080p signals.

But this PC connection uses the RGBHV signal type - that is, red, green, and blue along with separate horizontal and vertical sync pulses. Before buying this type of cable, therefore, you should ensure that the two devices you want to communicate via VGA will actually understand one another. In some cases, the VGA socket actually outputs a YUV signal, which will then once again need an adapter.

DisplayPort cables remain rare in the home-theater, despite their HDMI-compatibility.

The so-called DisplayPort is currently found primarily on Apple computers. On paper, this socket is equivalent to HDMI, and, in practice, it's possible to connect the two using an adapter. Since it's a VESA standard, it's cheaper in terms of royalties, and for this reason we're likely to see DisplayPort more often in the future. Looking less likely to make waves, on the other hand, is the DisplayLink connection, which uses USB and simulates an external graphics card in the display device.

Here are a few simple rules that you should always observe:

1. Position the devices so that the cables' paths can be kept as short as possible. The cable length is decisive for the picture quality!

2. Use HDMI cables whenever possible - primarily for the picture, but also for the sound (and especially for HD audio).

3. At the same level of quality, always choose the lowest bandwidth in the source device, and leave the up-scaling to the display - that is, if the display can do it just as well or better. For example: choose 24p instead of 1080p/60 for movies from a Blu-ray disc.

4. Always buy the shortest possible cables - that is, try and make sure the cables fit exactly, so that you don't end up with two or three meters of surplus cable crammed away somewhere.

5. Once you've chosen its path, fasten the HDMI cable in place so that movements and vibrations won't loosen the connections.

6. With long stretches of HDMI cable, use an amplifier or repeater - or arrange the devices differently, to split up the distance

7. If it's impossible to use an HDMI connection, you should ideally use YUV for the picture, or cinch connections for multichannel sound. These generally work without problems, but they're no longer future-proof.

8. Check the cables' fit regularly, and give them a clean - ideally with alcohol or contact spray.

9. Always lay cables a certain distance away from other devices or wiring.

10. Keep the ten-percent rule in the back of your mind: cables should cost around 10 percent of the price of the other devices.

Check all connections regularly!

Wireless connections:
Wireless HDMI connections are gaining in popularity. It's no wonder; after all, they get rid of all that nasty cable jungle. Sony, for example, presented a wireless solution at the start of 2009, but this proved to have a few weak points. Panasonic's technicians have done a better job: The company's current top plasma, the TX-P54 Z1, also uses wireless HDMI transmission - and very successfully, too! We can assume that, in the future, more and more manufacturers will venture into the territory of wireless solutions.

To summarize, the same rules apply to HDTV connections as generally apply to other cables. But the higher bandwidths and bit rates mean it's particularly important to follow the rules - if you want to avoid hitting problems.