10 - Compression
So far we have covered the common ways to get video from point A to point B. An important part of that once we get into the digital video world is compression. Although DVI and HDMI are not compressed and market themselves as better because of it, the lack of compression is actually their biggest problem. The faster the data rate, the shorter the distance you can go over a given information path.
Compression isn’t something that you will typically deal with as part of an installation project, but it is helpful to understand when selecting equipment, diagnosing video problems, and to better understand it’s capabilities.
Also helpful to understand is the state of current consumer gear as of this writing (Spring 2006). Compressing video in real time is possible with standard definition video. The amount of data is small enough that there are both cost effective hardware and software solutions to do this. For example, a stand alone Tivo can take composite or S-video on the back panel, compress it in real time, and have something small enough to reasonably fit onto a harddrive. However compressing HD video in real time is still only the domain of broadcast grade equipment. This is the reason there is no stand alone HD Tivo, or similar DVR boxes. If the only source of HD you have is component video (uncompressed analog) or HDMI (uncompressed digital), then there is no practical solution to recompressing it for the purpose of storing to harddrive, or sending through Firewire or IP networks.
So any compressed HD video you will run across was originally compressed by a cable or satellite provider back in their head end. Once it has been decompressed in the home it will have to stay decompressed, and not recordable, at least for now.
Next is a brief summary of the common compression methods in use.