In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth.[14] The operators may use format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.[15] Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance, which may be difficult because of customer confusion regarding connections.
You will have to buy the appropriate cable for example in most cases a HDMI cable or component cables. These are often more expensive. For instance, if Composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. HDMI provides the best picture and sound but are also generally more expensive than Component cables.
As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply here. For example, digital video responds differently to analogue video when subject to interference. As opposed to a lower-quality signal one gets from interference in an analogue television broadcast, interference in a digital television broadcast will freeze, skip, or display "garbage" information. Broadcasters may aggressively compress video to save bandwidth and therefore broadcast more channels - this compression manifests itself as reduced video quality.
In order to view HDTV broadcasts, viewers may have to upgrade their TVs which come at expense. Adding a new aspect ratio makes for consumer confusion if their display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition TV shows and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on a HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren't satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything a too-wide or not-tall-enough appearance. Alternately, they'll choose to zoom the image which removes content that was on the top and bottom of the original TV show.[16]
As of 2007, broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. That some satellite companies offer the local HD channels as a service at additional cost (transmission comes from satellite) suggests to some broadcasters that on-air broadcasts of local HD signals must be a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or have to install an antenna to receive the digital broadcasts. Such issues more entail economic and legal disputes than they entail technology.
Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD DVD vs. Blu-ray Disc high definition storage format war for a period of time created confusion for consumers. This particular format war was recently "settled" with Blu-ray emerging as the victorious standard.
http://en.wikipedia.org/wiki/High-definition_television
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