HDV: High Def Value (page 2)

MPEG-2 Compression

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 you…