SD or HD?
The most fundamental development in the last couple of years has been the arrival of high definition. All versions of DV - even the professionally oriented ones - use the same 720 x 576 resolution, at least in Europe and other PAL regions. This is called standard definition (SD) and shouldn't be confused with the Secure Digital memory format (also known as SD) that some camcorders record to. The more mathematical reader might notice that the SD horizontal and vertical pixels don't make up the expected 4:3 aspect ratio. In fact, each pixel is rectangular rather than square, also known as anamorphic, so that the resulting TV image is 4:3. It's also possible to set DV to 16:9 widescreen. The resolution remains the same, but the pixels are a different rectangle to form the wide aspect.
DV also uses interlaced fields rather than progressive frames - an age-old system dating back to the times when the systems used to scan the image onto a TV tube just weren't fast enough to complete a full frame in one go. Each frame was therefore divided up into alternate lines, with one set scanned first, then the other. So PAL video has 25 frames per second made of 50 interlaced fields.
High definition (HD), in contrast to SD, comes in two flavours and is supposed to have entirely square pixels to put it in line with the computer age. The two options are 1,280 x 720 and 1,920 x 1,080. The former is only ever found with progressive frames and is called 720p, but the latter can be interlaced or progressive, called 1080i and 1080p respectively. All of these offer a 16:9 widescreen aspect ratio as standard.
However, in the transition to consumer formats, the full resolution of 1,920 x 1,080 was considered too great, so we've seen the return of rectangular pixels in the shape of the 1,440 x 1,080 variant on 1080i. Although the official reason for this is to ease the pressure on data rates, in reality there's a hint of protection for higher-end professional formats hidden away in there as well.
Of course, camcorders aren't the only devices to shoot video these days. Phones and digital cameras are also trying to muscle in on the act. But the resolutions used generally revolve around standard PC display sizes, in particular VGA (640 x 480) or quarter VGA (320 x 240), and almost always with US/Japan-oriented frame rates - 30 or 15fps. As a result, they're not directly compatible with UK TVs, always requiring resizing and frame interpolation when edited on a PC or burnt to DVD. For this reason, we don't really recommend these devices for anything other than occasional video capture.
So SD and HD are the two basic camcorder types now on the market, but within each category there are now many options, with different recording media options. Let's start with SD.