DV and HDV compress images very differently. In DV, like HDCAM and Digital Betacam, the video-compression is purely intraframe, comparing and compressing within each individual image. It's the same kind of compression most photos use on the Internet (e.g., JPEG). Each frame is compressed independently. Since HDV is MPEG-2, it uses both intraframe and interframe compression. Interframe compression happens in what is called a GOP or group of pictures, made up of I, B and P frames. The I frame is encoded independently. The next frame to be encoded is a P or predictive frame, which anticipates changes in the video, discarding redundant information. Between the I and P frames, B or bi-directional frames fill in, looking both backwards and forwards. It's played back IBBPBBP, etc., with the next I frame determined by the size of your GOP. Since most video has redundancy across frames, the method works well until there is a lot of change. While shooting HDV, be wary of rapid camera motion, like fast pans, which can overwhelm the compression process.

Sony also recommends using its better quality HDV vs. DV tape. If you're unlucky enough to have a drop out on a recorded I frame, you have no back up immediately fore and aft. The glitch will affect everything in your GOP.

Editing HDV footage is more problematic than cutting DV. Since each DV frame is compressed independently, the footage can be cut at any frame without affecting those next to it. In HDV, the I frame, the only truly intact frame, is typically recorded once every half second or less. The rest are extrapolated across the GOP. Any transition while editing, even a simple cut, requires an entire decompression and then recompression of every frame in the GOP.

Non-linear HDV editing demands a lot of processing power to extract and then reconstruct an image at a transition. MPEG hardware encoding is usually cleaner and faster than software only, so consider investing in a dedicated HDV encoding board. Some will also give you real time playback on a monitor. No matter what edit system you choose, you'd be wise to get the most RAM and the fastest CPUs you can afford. The good news is that the file sizes will be as manageable as working in DV, so you don't have to buy the gig a minute of storage that uncompressed standard definition editing requires.

Compression issues are exacerbated if you are shooting in simulated 24p. If you've ever cut film that was telecined, you've seen the field complications that arise from a 3/2 pull down. Both Sony and Canon's HDV cameras do a reverse 2/3 which requires even more sophisticated processing with MPEG-2 during editing. These HDV modes can produce unintended motion artifacts. Some videographers planning to finish on film have opted for shooting in PAL mode at 25 fps. They find the 4% speed difference less objectionable than the processing errors caused by pseudo 24p.

Choose your HDV package based on your specific shooting needs. Each one has its tradeoffs.

Paul M. J. Suchecki writes for network TV and shoots and produces documentaries.

16:9 Aspect Ratio is the ratio of the width to height of an image.

Depth of Field is the front to back area of apparent focus in a shot. It is affected by focal length of the lens, iris size and camera to subject distance.

Intraframe Compression A technique that compresses the video by removing redundancy from individual video images.

Interframe Compression A technique that achieves compression of a video file by eliminating redundant data between successive compressed frames. In a shot sequence of a red balloon sailing across a blue sky, for example, most of the image stays the same and is redundant from frame to frame.

MPEG-2 refers to an interframe and intraframe compression scheme instituted by the Motion Picture Experts Group. It differs from other MPEG compressions in that it is used to encode audio and video for broadcast signals. MPEG-2 compression is used in numerous applications, notably DVD, HDV and satellite transmission.

Interlace Scanning (i) Picture a Venetian blind representing scan lines. The odd lines, like the slats of a blind, are all scanned in one field. The even are scanned next. Put together they make up one complete frame of video.

Progressive Scanning (p) This is a scanning method where the lines are scanned in numerical sequence from top to bottom. This action in video more closely simulates how film records information.

Megabits per second (Mbps) A number representing the amount of digital data moved through a single point within a second of time.