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DV

 
DV compatibility mark

Launched in 1995 with joint efforts of leading producers of video camera recorders, DV is a format for storing digital video.

 

DV Specification

The original DV specification, known as Blue Book, was standardized within the IEC 61834 family of standards. These standards define common features such as physical videocassettes, recording modulation method, magnetization, and basic system data in part 1. Part 2 describes the specifics of 525-60 and 625-50 systems. The IEC standards are copyrighted publications available for purchase from IEC or ANSI.

 

DV Compression

DV uses lossy compression of video while audio is stored uncompressed.An intraframe video compression scheme is used to compress video on a frame-by-frame basis with the discrete cosine transform (DCT).

Closely following ITU-R Rec. 601 standard, DV video employs interlaced scanning with the luminance sampling frequency of 13.5 MHz. This results in 480 scanlines per complete frame for the 60 Hz system, and 576 scanlines per complete frame for the 50 Hz system. In both systems the active area contains 720 pixels per scanline, with 704 pixels used for content and 16 pixels on the sides left for digital blanking. The same frame size is used for 4:3 and 16:9 frame aspect ratios, resulting in different pixel aspect ratios for fullscreen and widescreen video.

Prior to the DCT compression stage, chroma subsampling is applied to the source video in order to reduce the amount of data to be compressed. Baseline DV uses 4:1:1 subsampling in its 60 Hz variant and 4:2:0 subsampling in 50 Hz variant. Low chroma resolution of DV (compared to higher-end digital video formats) is a reason this format is sometimes avoided in chroma keying applications, though advances in chroma keying techniques and software made producing quality keys from DV material possible.

Audio can be stored in either of two forms: 16-bit Linear PCM stereo at 48 kHz sampling rate (768 kbit/s per channel, 1.5 Mbit/s stereo), or four nonlinear 12-bit PCM channels at 32 kHz sampling rate (384 kbit/s per channel, 1.5 MBit/s for four channels). In addition, the DV specification also supports 16-bit audio at 44.1 kHz (706 kbit/s per channel, 1.4 Mbit/s stereo), the same sampling rate used for CD audio. In practice, the 48 kHz stereo mode is used almost exclusively.


 

Digital Interface Format

The audio, video, and metadata are packaged into 80-byte Digital Interface Format (DIF) blocks which are multiplexed into a 150-block sequence. DIF blocks are the basic units of DV streams and can be stored as computer files in raw form or wrapped in such file formats as Audio Video Interleave (AVI), QuickTime (QT) and Material Exchange Format (MXF). One video frame is formed from either 10 or 12 such sequences, depending on scanning rate, which results in a data rate of about 25 Mbit/s for video, and an additional 1.5 Mbit/s for audio. When written to tape, each sequence corresponds to one complete track.

Baseline DV employs unlocked audio. This means that the sound may be +/- ⅓ frame out of sync with the video. However, this is the maximum drift of the audio/video synchronization; it is not compounded throughout the recording.


 

Variants

Sony and Panasonic have created their proprietary versions of DV, which use the same compression scheme, but improve on robustness, linear editing capabilities, color rendition and raster size.
All DV variants except for DVCPRO Progressive are recorded to tape within interlaced video stream. Film-like frame rates are possible by using pulldown. DVCPRO HD supports native progressive format when recorded to P2 memory cards.


DVCPRO

DVCPRO compatibility mark

DVCPRO, also known as DVCPRO25, is a variation of DV developed by Panasonic and introduced in 1995 for use in electronic news gathering (ENG) equipment.

Unlike baseline DV, DVCPRO uses locked audio and 4:1:1 chroma subsampling for both 50 Hz and 60 Hz variants to decrease generation losses. Audio is available in 16-bit/48 kHz precision.

When recorded to tape, DVCPRO uses wider track pitch - 18 μm vs. 10 μm of baseline DV, which reduces the chance of dropout errors when video is being recorded to tape. Two extra longitudinal tracks provide support for audio cue and for timecode control. Tape is transported 80% faster compared to baseline DV, resulting in shorter recording time. Long Play mode is not available.


DVCAM

DVCAM compatibility mark

In 1996 Sony responded with its own professional version of DV called DVCAM.Like DVCPRO, DVCAM uses locked audio, which prevents audio synchronization drift that may happen on DV if several generations of copies are made.When recorded to tape, DVCAM uses 15 μm track pitch, which is 50% wider compared to baseline. Accordingly, tape is transported 50% faster, which reduces recording time by one third compared to DV. Because of the wider track and track pitch, DVCAM has the ability to do a frame accurate insert tape edit, while DV may vary by a few frames on each edit compared to the preview.


DVCPRO50

DVCPRO50 compatibility mark

DVCPRO50 was introduced by Panasonic in 1997 for high-value electronic news gathering and digital cinema, and is often described as two DV-codecs working in parallel.The DVCPRO50 doubles the coded video data rate to 50 Mbit/s. This has the effect of cutting total record time of any given storage medium in half. Chroma resolution is improved by using 4:2:2 chroma subsampling.DVCPRO50 is used in many productions where high definition video is not required. For example, BBC used DVCPRO50 to record high-budget TV series, such as Space Race (2005) and Ancient Rome: The Rise and Fall of an Empire (2006).A similar format, D-9, offered by JVC, uses videocassettes with the same form-factor as VHS.Comparable formats include Sony's Digital Betacam, launched in 1993, and MPEG IMX, launched in 2001.


DVCPRO Pogressive

DVCPRO Progressive compatibility mark

DVCPRO Progressive was introduced by Panasonic for news gathering, sports journalism and digital cinema. It offered 480 or 576 lines of progressive scan recording with 4:2:0 chroma subsampling and four 16-bit 48 kHz PCM audio channels. Like HDV-SD, it was meant as an intermediate format during the transition time from standard definition to high definition video.The format offered six modes for recording and playback: 16:9 progressive (50 Mbit/s), 4:3 progressive (50 Mbit/s), 16:9 interlaced (50 Mbit/s), 4:3 interlaced (50 Mbit/s), 16:9 interlaced (25 Mbit/s), 4:3 interlaced (25 Mbit/s).The format has been superseded with DVCPRO HD.


DVCPRO HD

DVCPRO HD compatibility mark

DVCPRO HD, also known as DVCPRO100 is a high-definition video format that can be thought of as four DV codecs that work in parallel. Video data rate depends on frame rate and can be as low as 40 Mbit/s for 24 frame/s mode and as high as 100 Mbit/s for 50/60 frame/s modes. Like DVCPRO50, DVCPRO HD employs 4:2:2 color sampling.DVCPRO HD uses smaller raster size than broadcast high definition television: 960x720 pixels for 720p, 1280x1080 for 1080/59.94i and 1440x1080 for 1080/50i. Similar horizontal downsampling is used in many other HD formats. To maintain compatibility with HDSDI, DVCPRO100 equipment upsamples video during playback.Variable framerates (from 4 to 60 frame/s) are available on VariCam camcorders. DVCPRO HD equipment offers backward compatibility with older DV/DVCPRO formats.When recorded to tape, DVCPRO HD uses the same 18 μm track pitch as other DVCPRO flavors. A long play variant, DVCPRO HD-LP, doubles the recording density by using 9 μm track pitch.DVCPRO HD is codified as SMPTE 370M; the DVCPRO HD tape format is SMPTE 371M, and the MXF Op-Atom format used for DVCPRO HD on P2 cards is SMPTE 390M.While technically DVCPRO HD is a direct descendant of DV, it is used almost exclusively by professionals. Tape-based DVCPRO HD cameras exist only in shoulder mount variant.A similar format, Digital-S (D-9 HD), is offered by JVC and uses videocassettes with the same form-factor as VHS.The main competitor to DVCPRO HD is HDCAM, offered by Sony. It uses a similar compression scheme but at higher bitrate.

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