All Things HDV Buyer's Guide (page 5)

Sidebar: HD/HDV TERMS

HDV: A low-cost alternative to uncompressed HD (high definition), developed in September 2003 by JVC, Sony, Canon, and Sharp. The HDV format records high-definition MPEG-2 transport streams to Mini DV tapes.

HDV uses long GOP (group of pictures), which contains an I-Frame, or Intra-Frame compressed image, once every 15 frames. The P- and B-Frames (or Predictive and Bi-Directional) will reference images and data that don't change from the I-Frame. For instance, if a person is walking outside, the only part of the frame that is re-drawn and not referenced to the I-frame is the person who is walking. This keeps the data small enough to go to Mini DV tape.

AVCHD: Advanced Video Codec-High Definition; another type of compression for HD production. Instead of HDV's mandate of recording to tape, AVCHD records to either a DVD disc, a Hard Drive Disk (HDD), or a memory card. Developed by Sony and Panasonic in mid-2006, AVCHD is compressed to MPEG-4 using H.264 encoding, and it has some similarities to HDV, such as a 4:2:0 sampling.

DVCPRO HD: An HD codec developed by Panasonic that includes both 1080i/p and 720p, but when going to tape or P2 card, the 1920x1080 signal is down-sampled to 1280x1080, and 1280x720 is down-sampled to 960x720. This keeps the overall "size" of the HD signal small. Upon output to TV, DVD, etc., the signal goes back to its original sizes.

P2: Professional Plug-In; a storage device developed by Panasonic as a low-cost alternative to a more expensive DVCPRO HD tape deck. Each card is about the size of a credit card and can store, as of early 2007, up to 8 gigabytes (GB) of video each.

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