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DV (video format)

DV (Digital Video) is a family of codecs and tape formats used for storing digital video, launched in 1995 by a consortium of video camera manufacturers led by Sony and Panasonic. It includes the recording or cassette formats DV, MiniDV, DVCAM, Digital8, HDV, DVCPro, DVCPro50 and DVCProHD. DV has been used primarily for video recording with camcorders in the amateur and professional sectors.

Media type

1995 (1995)

DV was designed to be a standard for home video using digital data instead of analog.[1] Compared to the analog Video8/Hi8, VHS-C and VHS formats, DV features a higher video resolution (on par with professional-grade Digital Betacam) and also records audio digitally at 16-bit like CD.[2] The most popular tape format using a DV codec was MiniDV; these cassettes measured just 6.35 mm/¼ inch, making it ideal for video cameras and rendering older analog formats obsolete.[2] In the late 1990s and early 2000s, DV was strongly associated with the transition from analog to digital desktop video production, and also with several enduring "prosumer" camera designs such as the Sony VX-1000.[3]


In 2003, DV was joined by a successor format called HDV, which used the same tapes but with an updated video codec with high-definition video; HDV cameras could typically switch between DV and HDV recording modes.[4] In the 2010s, DV rapidly grew obsolete as cameras using memory cards and solid-state drives became the norm, recording at higher bitrates and resolutions that were impractical for mechanical tape formats. Additionally, as manufacturers switched from interlaced to superior progressive recording methods, they broke the interoperability that had previously been maintained across multiple generations of DV and HDV equipment.

Development[edit]

DV was developed by the HD Digital VCR Association: in April 1994, 55 companies worldwide took part, which developed the standards and specifications of the format.[5]


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 video systems supporting 525-60 for NTSC and 625-50 for PAL.[6] The IEC standards are available as publications sold by IEC and ANSI.

DV compression[edit]

DV uses lossy compression of video while audio is stored uncompressed.[7] An intraframe video compression scheme is used to compress video on a frame-by-frame basis with the discrete cosine transform (DCT).


Closely following the 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.[8][9]


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 the 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 have made producing quality keys from DV material possible.[10][11]


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.[12] In practice, the 48 kHz stereo mode is used almost exclusively.

Digital Interface Format[edit]

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).[13][14] 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.[8]


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.

Sony family of cameras can record DV onto either Professional Disc or SxS memory cards.

XDCAM

Panasonic DVCPRO HD and AVC-Intra camcorders can record DV (as well as DVCPRO) onto cards.

P2

Some Panasonic camcorders (AG-HMC80, AG-AC130, AG-AC160) record DV video onto Secure Digital memory cards.

AVCHD

JVC GY-HM750 can be set to standard definition mode and in this case will record '.AVI or .MOV SD legacy format' video onto SDHC cards. For clarity - and contrary to what has previously been written, the camera does not natively support SxS memory cards, has no slots for them and requires an optional add-on recorder (or 'adapter' as JVC call it) to achieve this - basically this camera is an 'XDCAM EX' High definition unit and the add-on SxS recorder was only made available to achieve better compatibility in facilities which were Sony based.

Most DV and camcorders can feed live DV stream over IEEE 1394 interface to an external file-based recorder.

HDV

(Hideaki Anno—1998)

Love & Pop

(Bennett Miller—1998)

The Cruise

(Agnès Varda—2000)

The Gleaners and I

(Miguel Arteta—2000)

Chuck and Buck

The Gleaners and I: Two Years Later (—2002)

Agnès Varda

(Danny Boyle—2002)[37]

28 Days Later

(David Lynch—2006)

Inland Empire

(James Longley—2006)

Iraq in Fragments

(Jaume Balagueró & Paco Plaza—2007)

Rec

My First Kiss and the People Involved (Luigi Campi & Giacomo Belletti—2016)

Application software support[edit]

Most DV players, editors and encoders only support the basic DV format, but not its professional versions. The exception to this being that most (not all) consumer Sony miniDV equipment will play mini-DVCAM tapes. DV Audio/Video data can be stored as raw DV data stream file (data is written to a file as the data is received over FireWire, file extensions are .dv and .dif) or the DV data can be packed into container files (ex: Microsoft AVI, Apple MOV). The DV meta-information is preserved in both file types being Sub-timecode and Start/Stop date times which can be muxed to Quicktime SMPTE standard timecode.


Most Windows video software only supports DV in AVI containers, as they use Microsoft's avifile.dll, which only supports reading avi files. Mac OS X video software support both AVI and MOV containers.

Mixing tapes from different manufacturers[edit]

There was considerable controversy solely based on hearsay over whether or not using tapes from different manufacturers could lead to dropouts.[38][39] Initially this was suggested around the conception of mostly MiniDV tapes in the mid to late 90s as the only two manufacturers of MiniDV tapes (Sony, who produce their tapes solely under the Sony brand; and Panasonic, who produce their own tapes under their Panasonic brand and outsources for TDK, Canon, etc.) used two different lubrication types for their cameras - Sony uses a 'wet' lubricant ('ME' or 'Metal Evaporated'), while Panasonic uses a 'dry' lubricant ('MP' or 'Metal Particle').


The standard practice for casual and professional camera operators alike is not to mix brands of tapes. (as the different lubrication formulations can cause or encourage tape wear if not cleaned by a cleaning cassette) No significant problems have occurred for the last few years - meaning that switching tapes is acceptable, though sticking to one brand (and cleaning the heads with a cleaning cassette before doing so) is highly recommended.


A research undertaken by Sony claimed that there was no hard evidence of the above statement. The only evidence claimed was that using ME tapes in equipment designed for MP tapes can cause tape damage and hence dropouts.[40] Sony has done a significant amount of internal testing to simulate head clogs as a result of mixing tape lubricants, and has been unable to recreate the problem. Sony recommends using cleaning cassettes once every 50 hours of recording or playback. For those who are still skeptical, Sony recommends cleaning video heads with a cleaning cassette before trying another brand of tape.

SIF (Source Input Format)

CIF (Common Intermediate Format)

Video CD

Adam Wilt's DV page with in-depth technical information