The HD Specification
So what is HD? Hi-definition video is more than just a name to indicate an image has higher resolution than previous video forms, rather HD is a specific technical specification that all major hardware manufacturers and software developers have agreed upon for the future of film, TV, video and broadcasting.
The HD specification dictates a number of areas of the HD format but most particularly and importantly it specifies the frame size and dimensions of the image. Existing Standard Definition (SD) has fixed dimensions of 720 pixels wide x 576 pixels high for PAL and 720×480 for NTSC. The HD spec allows for two different HD frame sizes; a smaller 1280×720 and a larger 1920×1080. The larger of these being nearly three times the size of SD.
These two size specs are commonly referred to as “720” and “1080” and of the two, the later, larger frame is quickly becoming the dominant standard for both HD TV’s and for camera shooting formats. Currently only JVC outputs the smaller 720 size for HD – all other manufacturers, including Sony, Canon, and Panasonic output a 1080 image.
There is another factor to the two frame size specifications; “progressive scan” and “interlaced” images. HD 1280×720 is a progressive scan image and this is often indicated by the use of a “p” next to the 720 (720p). A progressive scan image is one where each frame is composed of a single, solid picture. 1920×1080, by contrast, is, most often, an interlaced image (referred to as 1080i) whereby the image is made up of two interlaced fields at half second intervals which together make up the full frame rate. There is much debate over which type of image looks ?better? but the distinction is marginal. The overwhelming majority of HD equipment manufacturers; from cameras, to software, to TV?s, are focused on 1080. Also all TV display devices can scale very effectively to accommodate both so there are few issues regardless of which format you work in. The grail of course is 1080p which has the best of both worlds ? both large frame and progressive.
This all sounds fine and dandy; HD is a much bigger picture and a much sharper image. There is of course a catch however and that?s the sheer amount of data a HD video file takes up and how much bandwidth it requires to be viewed without stuttering. Uncompressed HD at full 1920×1080 is just too monstrously huge to be captured, handled or even played back by anything but the most powerful, professional production systems. So, in order to make HD viable and efficient it needs to be compressed.
There are currently two major compressed HD video formats for consumers and prosumers widely available in a variety of cameras, from the very cheap to the relatively expensive. The first is and the second, and newest, is AVCHD.
Short, obviously, for High Definition Video, was introduced in 2004 and offered the first viable HD format available in inexpensive cameras. In order to make the HD format more manageable, applies two very important and clever processes to the signal to reduce its size without overly reducing image quality.
One of the downsides of MPEG-2 compression is that when editing the footage the video files have to be unpacked and the frames rebuilt on the fly by the editing software as you work. This makes HDV editing very system intensive and requires relatively powerful computers to work efficiently. That said with dual-core computer CPU?s now the standard any machine bought now or in the past year or two should be more than capable of editing HDV.
Short for Advanced Video Codec High Definition, AVCHD is the newest HD format to be released for inexpensive HD video production. Where tend to more expensive and professional in features, AVCHD is intended to become the new standard for HD for everyday home movie use.