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High Definition Video ('''HDV''') is a Video format designed to record compressed HDTV video on standard DV media (DV or MiniDV cassette tape). HDV Camcorder ]] HISTORY The HDV format was developed by JVC and supported by four companies: Canon Inc. , Sharp Corporation , Sony Corporation , and Victor Company of Japan, Limited ( JVC ). These companies originally announced their HDV partnership in September, 2003 . They have since been joined by other companies, notably Apple Computer . JVC's GR-HD1 was the first camcorder based on HDV specifications with 720p . In September 2004, Sony launched their first consumer HD camera, the Sony HDR-FX1 , which can record the 1080i 60 format (the PAL version records 1080i50) on a MiniDV tape using the HDV format. The professional version of this camera has both 50i and 60i capabilities, and adds XLR audio plus about 25 more features and is called the Sony HVR-Z1U . In 2005, Sony released the consumer-oriented HDV Camcorder, the HDR-HC1 . A professional version of the HC1 the Sony HVR-A1E was released in autumn 2005. In 2006, Sony replaced the HDR-HC1 with the HC3, more consumer-oriented, a bit cheaper, a slightly improved CMOS chip but with less specifications. Canon introduced its first HDV camcorder, the Canon XL-H1 , in September 2005. In late 2005, Panasonic took a different approach by introducing its Panasonic AG-HVX200 HDTV camcorder that records HD on the Panasonic's own DVCPRO-HD format. DVCPRO-HD requires four times the bandwidth of HDV (100mbs versus 25mbs for HDV) but suffers less from compression and motion artifacts. The HVX200 records its HD signals on DVCPRO P2 Cards only, with the Mini DV tape recorder for standard definition DV only. The camera also has an interface for directly recording DVCPRO-HD data on Hard Disk . OVERVIEW HDV was designed to offer existing video-production environments a cost-conscious path from SD to HD environments. HDV production equipment, being constrained to the 25 Mbit/s Bitstream Rate of standard DV, is much less expensive than equipment based on professional standards such as HDCAM and DVCPROHD . HDV's main benefit is low-cost video acquisition, as HDV-camcorders can be built and operated at costs closer to conventional DV. Furthermore, inexpensive Mini-DV cassettes are the storage medium for most HDV camcorders. This opens high-definition video acquisition to consumers, amateur videographers, and low-budget TV production. The use of MPEG 2 compression allows HDV to deliver a far higher quality picture than DV at the same 25 Mbit/s data rate. (This is due to more pixels.) It is also theoretically higher than broadcast HD, which also uses MPEG 2, but is limited to 19 Mbit/s in the US. (Or significantly less if multicasting is used.) However, the HDV image has lower quality and more artifacts than the high-data-rate professional HD standards mentioned above, and MPEG's interframe nature makes editing more complex. Because of the use of the lossy MP2 codec, audio quality is somewhat lower than that of standard DV. Since the bitrate of the HDV bitstream is the same as conventional DV25, recording-times for HDV are the same as for DV. That is, a 60 minute MiniDV cassette can store 60 minutes of either DV or HDV footage. HDV supports several , 25p, 30p, 50i, or 60i.''' HDV COMPRESSION In terms of compression strategy, DV and HDV are very different. In DV, the video-compression is purely intraframe (spatial). Each video frame is recorded separately with equal file sizes and physical placement on the videotape. HDV, a constrained form of MPEG-2 video, employs both intraframe and interframe (temporal) techniques. Frames are recorded in groups of 12(PAL) or 15(NTSC), with unchanging or predictably moving areas recorded once and shared across frames. The result is higher compression ratios than possible with a purely intraframe technique, but at the risk of increased artifacts in complex moving scenes. Motion artifacts become increasingly noticeable as high-definition screens gain in size, brightness, and overall quality. HDV renders more crisply than DV on typical consumer displays. DV tends to look rather blurry when scaled up to HD resolutions. RESOLUTION AND ASPECT RATIO In HDV, the video frame is defined to have an Aspect Ratio of 16:9. Permitted resolutions are 720p and 1080i. HDV 1080i, like other new HD recording formats, uses a Pixel Aspect Ratio of 1.33 to store data in a more mathematically and algorithmically efficient way. HDV 1080i uses a pixel resolution of 1440x1080, but when displayed has an effective resolution of 1920x1080 = (1440 x 1.33)x1080. Visually, the images are considered to be equal, as the spatial resolution of the human eye is less sensitive to differences in horizontal resolution than vertical resolution. Both HDCAM and DVCPROHD also use rectangular pixels, so HDV footage can be imported into existing HD-production flows without rescaling. Even though using "only" 1440x1080 pixels for 1080i, the perceived sharpness with HDV is much higher than with PAL or NTSC DV formats. 1440 is still twice the horizontal resolution of DV and DVD formats. In total 1080i has a resolution of 1,555,200 pixels, which is 4.5 times larger than the resolution of NTSC-DV (345,600 pixels) and 3.75 times larger of PAL-DV (414,720 pixels). This applies to the brightness information only, because color information (hue and saturation) is always for HDV) to reduce data, be it HDV, DVD, DV or a professional video format because the Human Eye has less color resolution than brightness resolution. The color resolution of PAL/NTSC/DVD and HDV is only a quarter of their luminance resolution. NOTES REGARDING SPECIFIC CAMCORDER MODELS Canon's XL-H1 prosumer HDV camcorder simulates a progressive capture (which they denote by "F") at the lower frame rates: 24F, 25F, 30F. They achieve this by doubling the horizontal scan-rate to scan the interlaced sensor twice in one cycle. This lets them use a less expensive sensor at the expense of some interlacing artifacts. There will be fewer artifacts than 50i/60i, but it will not be as smooth as true 25P/30P. EDITING HDV As a consequence of the fact that HDV uses the interframe MPEG-2 GOP (Group Of Pictures) structure instead of a solely intraframe compression system, native Editing of HDV footage differs technically from the native editing of DV footage. In DV, as each frame of a video sequence is stored as an independent object, the recorded footage can be spliced at any frame without any loss of quality. When editing HDV's MPEG-2 data directly, a single frame cannot be changed without re-encoding subsequent frames from the same group. Any editing of the native MPEG-2 video, whether it be a complex transition or a simple scene-change, requires a decompression and recompression of the entire HDV frame group. Especially over many generations, this may result in increased artifacting, for example in the next frame group after a splice. However, because HDV's bitrate is 25 MB/s, these should be not as obvious as those seen when lower bitrates, such as those used for encoding clips for download, are used. If HDV footage is converted to a good intermediate format for editing, these considerations will not necessarily apply, and given a good quality intermediate format and codec, gradual degradation from generation to generation of edit may be avoided. Editing software support See also Non-linear Video Editing For Mac OS X:
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SPECIFICATIONS SEE ALSO
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