Double Feature

Format follies

In the video industry, most digital camcorders record DV-format video onto miniDV tapes or Hi8 tapes. But digital camera makers have not agreed on a single format for video capture. So while it's easy to get footage from a DV camcorder into your computer for editing or viewing on a TV, the wide variety of formats and compression schemes used by digital cameras is downright maddening. Recording formats include Apple's QuickTime (.mov), Window's Media (.avi), and several MPEG (.mpg) and JPEG (.jpg) choices.

The amount of compression is also an important factor. Most digital cameras include controls for changing the compression level of still images, but none (so far) let you adjust the compression level of video. DV camcorders compress video at a 5:1 ratio, so a second of video requires about 3.5 megabytes to store. At this level, details remain sharp and few artifacts appear even when viewed on High Definition televisions. Digital cameras have to shrink video and sound data to fit onto small, rather slow memory cards or into limited RAM buffers. That's why even the best digital cameras we've tested store video at 12:1, while the worst approach 100:1 and are rife with artifacts.

In addition, a variety of compression algorithms and levels used can affect quality and compatibility with editing programs. For example, 320x240-pixel, 15-fps video clips captured by the Olympus Camedia D-580, and saved using the camera's Photo-JPEG compression, refused to open in some editing software until we resaved them using M-JPEG compression, with Apple's QuickTime Pro software. If you're planning to edit video from a variety of cameras or camcorders, we recommend upgrading the free version of QuickTime Player to the Pro version (www.apple.com; $29). This program works with Macs and PCs and lets you view nearly every type of video, plus reformat your movies for use on the web or in DV-editing software.

Other, less obvious factors that affect video quality are the color-bit depth and sampling rate of the audio. In most cases, digital cameras capture color at the same 24 bits (or 16.7 million colors) as they do with still images. But some cameras (such as the Canon PowerShot A70) drop to 16-bit color in video mode. Sound also varies in quality, with the better models capturing 16-bit sound at a 32-44 Hz sampling rate, while lower-end cameras capture 8-bit sound at 8 Hz.

Video dictionary

Frame rate: the number of images captured per second. 30 frames per second (fps) appear as smooth motion video when played on a TV.

Video resolution: DV camcorders capture 720x480 pixels per frame in video mode and 640x480 pixels (VGA) in still mode. Some still cameras achieve this res, but others capture 320x240 pixels (QVGA) per frame or less.

Compression ratio: compares the size of uncompressed video data to the size of stored data. Generally, the lower the ratio, the higher the image quality.

Tips for shooting video with a still camera

1) Don't shoot vertical in video mode.

2) Use a tripod to minimize shake.

3) Use the highest-quality video-resolution setting, unless you're running low on memory. You can always resize clips later to send as video e-mail.

4) Don't overzoom during video recording (if you can zoom at all).

5) Keep clips short and stop between action instead of leaving the camera on.

6) Set manual white balance when possible before shooting.

7) Get closer to your subject in order to improve sound quality.