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 Mini DV HD/HDV Tapes
Please visit The Video Advisor for more information about DV Filming.
In an era of high definition, where HDV is recorded on DV tapes only a quarter-inch in width, the need to raise the performance of the media has never been more important. If you consider that a mini-sized tape that traditionally stores 60 minutes of standard definition DV/MiniDV is now commissioned to store 60 minutes of high definition HDV, you might wonder, how is that possible? The answer lies in the type of compression employed by HDV that effectively reduces the uncompressed video signal to the same 25Mbps (25 million bits/sec.) video bit rate as that of consumer DV. Hence, it is a misconception that more data is recorded to the tape with HDV than with DV.
What is HDV?
The HDV specification embraces two types of high definition recording, 720p at a video bit rate of 19Mbps, and 1080i at a rate of 25Mbps. A 1080/60i HDV signal (1440 x 1080) is made up of 1080 lines of vertical resolution (number of lines from the top of the screen to the bottom), each line containing 1440 pixels of horizontal resolution, displayed at a rate of 60 interlaced fields, or 30 frames, per second. Standard definition DV records a 480/60i signal (720 x 480) in NTSC countries, which includes the U.S. These resolutions render the HDV uncompressed video bit rate at roughly 4.5x that of consumer DV. In order to reduce the uncompressed video bit rate to DV’s compressed 25Mbps, HDV adopts the same powerful MPEG-2 compression format that is used for digital broadcasts and DVDs. MPEG-2 for HDV combines intra-frame (intra = within frames) compression, used in DV recording with, the more efficient, inter-frame (inter = between frames) compression. Inter-frame compression organizes frames into groups of pictures (GOPs) or frames, where one GOP is equivalent to about 15 frames, or a half-second of video. Each GOP begins with one intra-frame (I-frame) containing a complete frame of video, similar to a frame of DV video, followed by predictive and bi-directional frames which encode only the changes in the incoming video relative to the complete I-frame. By exploring redundancies within each frame, in addition to between frames, the MPEG codec is capable of compression ratios in excess of 20:1, compared to only 5:1 for DV. This means that less than 5% of the uncompressed HDV video signal is actually recorded to tape, compared to 20% with DV. It also means that the impact of missing data with HDV is much greater than with DV. The video bit rates may be similar, but the importance of each recorded bit is not. The interdependency of all the frames in the GOP, to successfully reconstruct the GOP in its entirety, puts greater demands on the tape to maintain bit-for-bit signal integrity during playback. Errors and dropouts can not only compromise the reconstruction of a single frame, but can affect the decoding of the for HDV? Why entire GOP, causing blocks, freeze frames or audio dropouts to occur. HDV needs a high performance tape.
*Note: Sony's Hardware Media Compatiblility Guide
Please scroll down to select our HDV Mini DV HD Tapes
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HDV 720p/HDV 1080i HDV Format Specification Table
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