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HDV

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HDV can also mean Hepatitis D virus.
High Definition Video (HDV) is a video format designed to record compressed HDTV video on standard DV media (DV or MiniDV cassette tape).
A Sony HDR-FX1 HDV camcorder
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A Sony HDR-FX1 HDV camcorder

Contents

History

The HDV format was developed by Victor Company of Japan, Limited (JVC) and is supported by four other companies: Canon Inc., Sharp Corporation, and Sony Corporation. These three companies, all manufacturers of HDV hardware, originally announced their HDV partnership in September, 2003. They have since been joined by other companies, notably Apple Computer, maker of the popular Final Cut Pro and iMovie editing software.

JVC was the first to release an HDV camcorder, the GR-HD1. With the GR-HD1, the user could select standard-DV (480i), or HDV (720p30, 480p60) mode. Sony was next to launch an HDV camcorder. Introduced in September 2004, the Sony HDR-FX1 recorded in HDV 1080i format. Depending on the TV-standard in the released market, the unit would support either 50Hz or 60Hz recording (but not both.) The Sony HVR-Z1U, the equivalent professional model, supports both and adds XLR audio plus about 25 more features. 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 September 2005, Canon entered the HDV market with the Canon XL-H1, a professional, modular HDV-camera system. In 2006, Sony replaced the HDR-HC1 with the less-expensive HC3. The HC3 features a slightly improved CMOS chip, but omits some features (such as external mic-in) of its predecessor.

Panasonic, a major supplier of consumer and industrial DV equipment, took a different approach by pushing its DVCPRO-HD format for HD acquisition. The Panasonic AG-HVX200 HDTV camcorder records HD on DVCPRO P2 cards only. The built-in Mini DV tape-recorder is relegated to standard definition DV only. The AG-HVX200 supports an external interface for direct (DVCPRO-HD) to hard disk recording.

Overview

HDV was designed to offer existing video-production environments a cost-conscious upgrade path from standard-definition (SD) to high-definition (HD) video. Since HDV operates at the same recorded datarate (25 Mbit/s bitstream rate) as DV, HDV recorders share the same physical (MiniDV ) tape-transport as existing DV equipment. For the camera, the main expense is concentrated in the optics and imaging electronics. Compared to HD-video equipment built on more professional standards (such as HDCAM and DVCPROHD), HDV enjoys a tremendous cost advantage. HDV-camcorders opens high-definition video acquisition to consumers, amateur videographers, and low-budget TV production.

Although HDV and DV share the same (DV) tape format and the same recorded datarate, they use completely different video-compression technology. The DV codec is strictly an intraframe scheme, whereas HDV uses the well-established MPEG 2 video codec. MPEG-2 applies both intraframe and interframe to video-compression, allowing HDV to achieve its higher spatial-resolution at the target bitrate of 19 Mbit/s and 25 Mbit/s. Compared to more expensive HDCAM and DVCPROHD equipment, HDV suffers from significantly more spatial and temporal (motion) artifacts. As a consequence of interframe compression, HDV editing is more complex, and introduces greater distortion at the splice point (due to the interdependence of adjacent video frames.) Compared to conventional SD DV, HDV offers a much higher spatial resolution, so most observers are willing to accept the artifacts in exchange for a higher-definition picture. HDV-audio uses lossy-compression (MPEG-1 Layer 2) to reduce the audio-bitrate to 384Kbps. DV-audio uses uncompressed 16-bit PCM at 1536Kbps. As a result, HDV-audio is technically inferior, although MPEG-1@384Kbps is regarded as 'perceptually lossless.'

Since HDV and DV use the same DV25 tape-transport, at the same linear speed, recording-times for DV and HDV are identical. That is, a 60 minute MiniDV cassette can store 60 minutes of either DV or HDV footage. As of yet, no HDV cameras can record HDV at LP speed, so the maximum record time on one tape is 80 minutes, as opposed to 120 with an 80 minute tape at LP.

HDV compression

Although HDV and DV share the same (DV) tape format and the same recorded datarate, they use completely different video-compression technology. The DV codec is strictly an intraframe (spatial) compression. Each DV video frame is recorded as an independent picture, with a fixed bit allocation and uniform placement on the videotape. The HDV codec is based on MPEG-2 video compression, which employs both intraframe and interframe (temporal) techniques. In general, interframe compression examines changes between adjacent frames (in a sequence), and records the difference as a master (key) frame, and a predicted frame. Consequently, an HDV frame varies in size, and shares a complex dependency between a previous and future neighbor. From an abstract view, frame data is 'propogated' from one frame to the next, yielding better compression efficiency. HDV 1080i Frames are recorded in groups of 12(PAL) or 15(NTSC), allowing interframe-predictions to span that distance (within a group.)

MPEG-2 video enables HDV to achieve a much higher compression ratio than DV, but at the cost of motion-induced artifacts in scenes of complex-motion. The artifacts are a limitation of the compression technology and bitrate allocated to the video bitstream. Motion artifacts are imperceptible for static shots and gentle pans, but become increasingly detracting as motion complexity increases. For example, a moving riverbed may exhibit regions of picture breakup, depending on its portion of the total screen area. It is important to view these limitations in the proper context. For the DV-codec to approach the spatial-quality of HDV, it would require several times (>4x) the storage space.

Dropouts or errors in the compressed video bitstream affect HDV much more severely than DV. This is an unavoidable characteristic of interframe compression. Since frame data affects multiple frames (and not just the one it originated from), a dropout will impact all dependent neighbors. Frame-accurate editing is also made more difficult by the MPEG-2 codec. Any modifications to the video-sequence require the surrounding group of frames to undergo a complete (and lossy) decompression/recompression cycle.

For all its limitations, HDV can look quite stunning on a consumer HD display. Although free of motion-induced artifacts, DV tends to look fuzzy when scaled up to HD resolutions. Subjectively, most observers are willing to accept HDV's visual artifacts in exchange for a more detailed picture.

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 is scaled to an aspect ratio of 1920x1080 = (1440 x 1.33)x1080. While this reduces horizontal resolution, the loss is less than the numbers would suggest, because the vertical resolution is also reduced by interlace. The benefit of adding pixels is reduced if resolution in only one direction is increased, while the other lags too far behind.

HDV resolution, while falling short of 1080p, is still a dramatic improvement over standard DV. Box area denotes effective resolution, not the intended shape of the screen.
Enlarge
HDV resolution, while falling short of 1080p, is still a dramatic improvement over standard DV. Box area denotes effective resolution, not the intended shape of the screen.

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 subsampled ([[4:2:0#4:2:0|4:2:0]] 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. Also, various practical tests have shown that resolution in 24F/25F/30F progressive modes is lower than when 1080i interlaced is selected.

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 Mbit/s, these should be not as obvious as those seen when lower bitrates, such as those used for encoding clips for download, are used.

Editing HDV's native Mpeg2 transport stream files also forces the computer system to work much harder to perform even simple tasks of cutitng and splicing as frames that dont actually exist as independent cells have to be re-built by the NLE system on-the-fly.

If HDV footage is converted (known as 'Transcoding') to a good Lossless 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 as well as substantial system performance gains. The Apple Intermediate Codec (which runs out of Quicktime) is an efficient, easily usable codec for editing HDV in systems such as Final Cut Pro but lacks the transcoding and generational quality of some third-party HDV Intermediate codecs and does not offer any realtime performance assistance. Cineform's 'ConnectHD', 'AspectHD' and 'ProspectHD' intermediate codecs and encoding utilities currently offer the best HDV intermediate options which not only give lossless quality but also function within the rendering engine of some software editing systems (such as Premiere Pro) to boost real-time performance without hardware assistance. Cineform products currently work with Sony Vegas and Premiere Pro editing systems. LumiereHD offers a similar functionality for Mac based editing systems (namely Final Cut Pro) but without any real-time assistance.

There are many advantages to editing HDV using a Lossless Intermediate rather than the native Mpeg2 file however the trade off for transcoding to a HDV Lossless Intermediate is that the file size is substantially increased and so large hard drive arrays are required for storage of footage.

Editing software support

See also Non-linear video editing
For Mac OS X: For Microsoft Windows: Under Linux:

Specifications

Media DV or MiniDV Tape
Video signal 480/30p, 480/60p, 576/25p, 576/50p, 720/60p, 720/30p, 720/50p, 720/25p, 1080/60i, 1080/50i, 1080/25p, 1080/30p
Video sampling frequency for luminance 74.25 MHz, 55.7 MHz
Video Chroma subsampling [[4:2:0]]
Video sample quantization 8 bits (both luma and chrominance)
Video Compression MPEG2 Video (profile & level: MP@H-14)
Video compressed bitstream rate Approximately 25 Mbit/s for 1080i / 19 Mbit/s for 720p
Audio sampling frequency 48 kHz
Audio quantization 16 bits
Audio compression MPEG-1 Audio Layer II
Audio compressed bitstream rate 384 kbit/s
Audio mode Stereo (2 channels); optional 4-channel synchronous
MPEG Stream type Transport Stream Packetized Elementary Stream
Stream interface IEEE1394 FireWire (MPEG2-TS)
File extension Usually saved as .m2t or .mp2

See also

External links

Industrial & Home Video Media
Magnetic tape VERA (1952) - 2 inch Quadruplex videotape (1956) - 1 inch type A videotape (1965) - U-matic (1969) - Video Cassette Recording (1972) - Betamax (1975) - 1 inch type B videotape (1976) - 1 inch type C videotape (1976) - VHS (1976) - Video 2000 (1979) - VHS-C (1982) - M (1982) - Video8 (1985) - MII (1986) - D1 (1986) - S-VHS (1987) - D2 (1988) - D5 (1994) - Hi8 (199?) - S-VHS-C (19??) - W-VHS (1994) - DV (1996) - D-VHS (1998) - Digital8 (199?) - HDV (2003)

Optical discs Laserdisc (1978) - VHD (1983) - Laserfilm (1984) - CD Video (198?) - VCD (1993) - DVD (1996) - MiniDVD (?) - CVD (1998) - SVCD (1998) - FMD (2000) - EVD (2003) - UMD (2005) - HD DVD (2006) - Blu-ray Disc (BD) (2006) - AVCHD (2006?) - HVD (2010?)

 

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