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Table Of Contents
Understanding HDV
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Understanding HDV
HDV is a low-cost prosumer format that lets you record HD video onto standard DV
videocassettes. This is achieved through the use of interframe compression, where a given frame
in the video stream can be composed of information from adjacent frames. Frames are grouped
into a sequence called a “Group of Pictures,” or GOP. Long-GOP (also known as IPB encoding)
refers to the structure of HDV media.
A GOP contains several different types of compressed frames:
I frames, which are compressed frames that do not depend on any frames around them.
I frames anchor the beginning of the GOP.
P (predictive) frames and B (bidirectional) frames, which depend on the frames around
them.
Interframe compression is more efficient than frame-based schemes (such as DV 25), allowing
high-bandwith HD images to be contained on media designed for standard definition (SD).
However, HDV is more difficult to edit since frames are not independent of one another. Avid
provides a workflow that lets you edit natively with HDV-compressed video without requiring a
transcode to frame-based media, and without limiting where you make your cuts.
Your Avid editing application uses a technique called long-GOP splicing when encoding an
HDV MPEG-2 sequence for export. For more information, see “Long-GOP Splicing for HDV
Encoding” on page 1471.
HDV uses MPEG-2 video encoding and MPEG-1 audio encoding. 1080i records at about
25Mbps and 720p records at about 19Mbps. Sony provides HDV cameras that record at
1080i/59.94 and 1080i/50. JVC
®
cameras record at 720p/29.97 and 720p/23.976.
In some 1080i formats on qualified systems, you can reduce the data rate of the video before
compression by setting the video display (raster) to resize horizontally from 1920 x 1080 pixels
to 1440 x 1080 pixels or to 1280 x 1080 pixels. In contrast, 720p projects use the standard HDV
raster size of 1280 x 720. A special resolution, DNxHD-TR (for Thin Raster), improves the
performance of 1080 HDV editing. This resolution matches the 1080i HDV raster size, reducing
artifacts that would come from repeated compressions when rendering effects and graphics.