Imagine being able to pick out individual fans in the crowd during a wide-screen baseball-game broadcast, or to see the intricate crosshatching of Martin Sheen’s tie as he addresses the nation during an episode of
The West Wing.
High Definition (HD) video promises such things—a wider field of view and much more image detail. Whether you’re interested in watching, creating, or just learning more about HD, now is a good time to start paying attention—prices for the equipment necessary to watch and make HD content are falling. Here, we’ll look at some of the technology behind HD; in our December issue, we’ll explore
HD creation on the Mac.
Formats Face Off
Standard NTSC (National Television System Committee) video has 720 horizontal pixels and 486 vertical pixels (480 vertical pixels for compressed formats such as DV and MPEG-2) and has a frame rate of 30 (or, technically, 29.97) frames per second. NTSC video is also interlaced—each video frame is made up of two distinct video fields. The first field contains the odd lines of an image; the second, the even lines. The aspect ratio of NTSC, or Standard Definition (SD), TVs is 4:3.
At the core of HD video is increased resolution. HD pushes the pixel count way up, most commonly to 1,280 by 720 pixels or 1,920 by 1,080 pixels. These HD types are usually referred to by vertical pixel count and whether frames are progressive or interlaced—for example, 720P format or 1080i format. There are roughly 350,000 pixels available in SD video; HD displays more than 2 million—this is why the sharpness of HD video is startling. HD can have a variety of frame rates, but HD broadcasting is usually 1080i at 30 fps or 720P at 60 fps. HD is also a wide-screen format, with a native aspect ratio of 16:9. Watching HD feels like a movie-theater experience. HD signals can also broadcast using Dolby 5.1-channel surround sound, the audio format used in most commercial DVDs.
HD content currently makes up a very small percentage of television broadcasts. But with HD network shows such as
Law & Order,
cable series such as
Six Feet Under,
and sports broadcasts such as ESPN baseball and the Olympics from Athens, HDTVs are becoming more than expensive eye candy. You can receive HD signals, encoded as MPEG-2 streams, via satellite, digital cable, or ATSC digital broadcasts (see
“What It Means: HD”
for a glossary of HD-related terms).
EyeTV 500 ($349) lets you watch, record, and save ATSC HD broadcasts, and the EyeTV software lets you edit out commercials and unwanted material. You can also download
John Dalgliesh’s free MMInputFamily driver, which allows Macs to work with
$199 Fusion HDTV3 Gold PCI card to display HD broadcasts. (At this time, there’s no way to view HD satellite or digital-cable signals on your Mac.)
There are no HD DVDs yet, but the DVD Forum, which brought you today’s DVD, has adopted an HD DVD standard, which can use H.264/AVC (Advanced Video Coding), Windows Media Video 9’s VC-9 technology, and MPEG 2.
What It Means: HD
The world of modern video is filled with confusing terms and unwieldy acronyms. Our glossary will help you sort it all out.
The proportions (width:height) of the viewing area on a monitor or a television screen. HD has a wide-screen, 16:9 ratio. SD has a narrower ratio—4:3.
ATSC: A digital-broadcasting standard developed by the Advanced Television System Committee (also refers to DTV and HDTV standards).
Digital TV (DTV): A television signal transmitted as digital information. HD video is digital, but not all digital broadcasts are HD.
Dolby Digital: Six-channel digital-audio standard, also called AC-3 or Digi-tal 5.1.
Enhanced Definition TV (EDTV): A progressive SD television that accepts the progressive output of some DVD players. Usually, these TVs also have a de-interlacer built-in. They are not HDTVs.
HDMI: High Definition Multimedia Interface—a digital connector.
HDTV-Ready: A TV that can display HD video if a separate HD decoder box is attached.
MPEG-2: Moving Picture Experts Group 2. A video-compression format used to condense HD and SD video, for smaller data rates in DVDs and broadcasting.
Terrestrial Broadcast: Traditional over-the-air broadcast.