HDTV on a Media Center? Yes and No
One of the most common questions we receive and one of the most confusing one to explain is whether or not Media Centers can â€œdoâ€ HDTV. The answer is yes and no. To explain this you have to understand the underlying technology of TV broadcasts, both digital and analog. Let’s take a closer look and let me explain.
Breaking down the HDTV â€œlingoâ€
To start, it helps to have a better understanding of HDTV transmissions, both terrestrial or over-the air and cable or satellite. There are four areas that we need to get a little more understanding about; the Broadcast Standard Committee, TV resolutions, CODECS and modulation and transmission of TV signals.
Before we examine these four areas, let’s define what HDTV is. HDTV is a term used to describe TV broadcast with a higher resolution than standard TV formats. Many times companies misuse the term. Be aware of resolution and refresh rates when purchasing an HDTV because HDTV describes a large spectrum of HDTV resolutions. Which we will discuss a little later in the article.
Who sets the standards for HDTV?
The first area we want to get a better understanding about is the group that defines the TV broadcast standards. The Advanced Television Systems Committee (ATSC) is the group that helped to develop the new digital television standards for the United States. Canada, Mexico, and South Korea have also adopted this standard and it is being considered by other countries. DVB is a set of internationally accepted open standards for digital broadcasts that is used internationally. It is more widely used but coexists with ATSC. ATSC is intended to replace the NTSC system and produce wide screen 16:9 images up to 1920Ã—1080 pixels in size. This is more than six times the display resolution of the earlier standard.
What Resolutions did they define HDTV?
The second area to examine more closely is the resolutions for HDTV. There are three basic display sizes for ATSC. Basic and enhanced NTSC and PAL image sizes 480 or 576 lines of resolution. Medium-sized images have 720 lines of resolution and are 960 or 1280 pixels wide (for 4:3, traditional version, and 16:9, wide screen version, aspect ratio respectively). The top tier has 1080 lines either 1440 or 1920 pixels wide (here, too, for 4:3 and 16:9 aspect ratio respectively).
Here is a quick list of the defined HDTV formats: 1720i50, 720i60, 720p24, 720p25, 720p30, 720p50, 720p60, 1080i50, 1080i60, 1080p24, 1080p25, 1080p30
1080i60 â€“ The number 1080 represents the number of vertical lines of resolution while the i or p represents interlaced or progressive scan. The 60 represents the number of frames per second.
What are CODECS?
CODECS are the third area which we need to look at. Encoding is the method of packaging audio or video information for transmission. CODECS encode a stream or signal for transmission, storage or encryption and decode it for viewing or editing.
ATSC is based on the MPEG-2 system. It should be noted that MPEG-2 defines an entire system of encoding and encapsulating information (a “transport”), and is not just a video compression algorithm. ATSC uses 188-byte MPEG-TS packets to carry data. This is the “raw” data that a decoder interprets, following demodulation and error correction of the data stream. 1080-line video is actually encoded with 1920Ã—1088 pixel frames, but the last eight lines are discarded prior to display. This is due to a restriction of the MPEG-2 video format.
Dolby Digital AC-3 is used as the audio codec. Also known as A/52 to the ATSC. It allows the transport of up to five channels of sound with a sixth channel for low-frequency effects (i.e. “5.1” configuration). In contrast, Japanese ISDB HDTV broadcasts use MPEG’s Advanced Audio Coding (AAC) as the audio codec, which also allows 5.1 audio output. DVB allows both.
Modulation and Transmission
The final area to examine is modulation and transmission of ATSC signals. ATSC signals are designed to use 6 MHz bandwidth just like NTSC television channels. Once the video signals have been compressed, the data stream can be modulated in a variety of manners depending on the method of transmission.
Terrestrial (local) broadcasters use a 8-VSB modulation that can transfer at a maximum rate of 19.39 Mbit/s, sufficient to carry several video channels and metadata depending on conditions. Cable television operators generally have a higher signal-to-noise ratio and can use 16-VSB or 256-QAM to achieve a throughput of 38.78 Mbit/s, using the same 6 MHz. In recent years cable operators have become accustomed to compressing standard resolution video for digital cable systems, making it harder to find duplicate 6 MHz channels for local broadcasters on uncompressed “basic” cable. Cable operators lobbied the Federal Communications Commission to allow 256-QAM in addition to the 16-VSB standard originally mandated. Though successful, cable operators have still been slow to add ATSC channels to their lineups.
Whewâ€¦â€¦! Ok now what does all this mean?
2 Ways to View HDTV Signal on a Media Center
There are 2 ways that a HDTV signal can be â€œdisplayedâ€ on a Media Center. One is with an ATSC tuner which can receive over-the-air HDTV broadcast signals. The other is viewing the HDTV signal that is decoded from a satellite or cable box then â€œpassedâ€ to the media center. Let’s take a look at each of these methods in detail and explain the advantages and disadvantages. I will also talk about the exciting technology that is on the horizon with HDTV.
First method â€“ ATSC (over-the-air) HDTV signal.
You must have an HDTV tuner card connected to a terrestrial antenna. This method is the only way that you can receive an HDTV signal and display it in its original resolution or format without any degrading of the signal. You will get your best picture quality using this method. The limitation is that most cities don’t have a large selection of free over-the-air broadcasts. Most of the broadcasts are just the prime stations (ABC, NBC, CBS, PBS and a few others). You will not get ESPN HD, Discovery HD or similar channels. These channels are only available from your local satellite or cable company which leads us to the second way to view HDTV content on the media center.
Second way â€“ Cable or Satellite connected to Media Center.
I know what you’re saying. You can’t get HDTV into a Media Center in its pure format. True. This method allows you to receive the pure HDTV digital signal into the cable or satellite receiver then pass the output of the cable or satellite box to the media center via S-VIDEO or COAX. This method degrades the HDTV signal so when you see the final picture on the screen, you see less than HDTV quality. Having said that, the picture you see may not be all that bad. It can depend on how good of a signal you are getting from your cable for satellite service, how large of a screen you are displaying the image on or how good your cable connections are. Example; in your particular area of the country you may get a better satellite reception versus cable. Combine that with the fact that you have a 36 inch standard TV. The â€œdegradedâ€ HDTV signal will look much better on your smaller TV than on a 60â€ DLP. We have demonstrated this to clients and the HDTV connoisseur can tell immediately but someone who is not exposed HDTV images and technology thinks the image is really pretty good.
What’s coming for Media Centers and HDTV I 2006?
The ideal situation is to be able to decode HDTV signal directly into the media center without having to go through a cable or satellite box. Microsoft has promised they will support this capability in the upcoming release of Windows Vista (Fall 2006) and ATI demoed the OCCUR at the 2006 CES in Las Vegas. This new TV tuner card will allow you to receive HD signal directly into your Media Center plus it has built in cable card support (CableCard 1.0). ATI has stated that this unit will work with all cable providers in the US. Visit www.ati.com to learn more about the new OCCUR tuner card and technology.
I hope that this article sheds some light on the sometime complex question about how media center can handle HDTV.
1 Information obtained from Wikipedia.com