DV

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A MiniDV camcorder and some MiniDV size Digital Video Cassettes

Digital Video (DV) is a digital video format created by Sony, JVC, Panasonic and other video camera producers, and launched in 1995. Its smaller tape form factor MiniDV has since become a standard for home and semi-professional video production; it is sometimes used for professional purposes as well, such as filmmaking and electronic news gathering (ENG). The DV specification (originally known as the Blue Book, current official name IEC 61834) defines both the codec and the tape format. Features include intraframe compression for uncomplicated editing and good video quality, especially compared to earlier consumer analog formats such as Video8, Hi8 and VHS-C. DV now enables filmmakers to produce movies inexpensively, and is strongly associated with independent film and citizen journalism^{[citation needed]}.

The high quality of DV images, especially when compared to Video8 and Hi8 which were vulnerable to an unacceptable amount of video dropouts and "hits", prompted the acceptance by mainstream broadcasters of material shot on DV. The low costs of DV equipment and their ease of use put such cameras in the hands of a new breed of videojournalists. Programs such as TLC's Trauma: Life in the E.R. and ABC News's Hopkins: 24/7 were shot on DV. CNN's Anderson Cooper is perhaps the best known of the generation of reporter/videographers who began their professional careers shooting their own stories.

There have been some variants on the DV standard, most notably Sony's DVCAM and Panasonic's DVCPRO formats targeted at professional use. Sony's consumer Digital8 format is another variant, which is similar to DV but recorded on Hi8 tape. Other formats such as DVCPRO50 utilize DV25 encoders running in parallel.

MiniDV tapes can also be used to record a high-definition format called HDV in cameras designed for this codec, which differs significantly from DV on a technical level as it uses MPEG-2 compression. MPEG-2 is more efficient than the compression used in DV, in large part due to inter-frame/temporal compression.^[1] This allows for higher resolution at bitrates similar to DV. On the other hand, the use of inter-frame compression can cause motion artifacts and complications in editing.^[2] Nonetheless, HDV is being widely adopted for both consumer and professional purposes and is supported by many editing applications using either the native HDV format or intermediary editing codecs.^[3]

DV Compression

The baseline variant of DV uses discrete cosine transform (DCT) to compress every video frame individually, with constant data rate of about 25 Mbit/s. DV compression is inherently lossy, and sometimes suffers from distortion around regions of rapid color or intensity changes, such as text and fine textures.

Before applying DCT compression, some color information is removed from original video. Such chroma subsampling is common for many video compression schemes and allows to reduce the amount of data to be compressed. Baseline DV uses 4:1:1 in its 60 Hz variant and 4:2:0 in 50 Hz variant. Relatively low chroma resolution is a reason why DV is sometimes avoided in chroma keying applications. Advances in chroma keying techniques and software made producing quality keys from DV material possible.^[4][5]

For audio, DV allows either two PCM channels (usually stereo) at 16-bit resolution and 48 kHz sampling rate, or four channels at 12-bit resolution and 32 kHz sampling rate. For professional or broadcast applications, 48 kHz is used almost exclusively. In addition, the DV specification includes the ability to record audio at 44.1 kHz, which is the same sampling rate used for CD audio, but this option is rarely used in practice.

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 differ in minor details.

DVCAM is a variation of DV developed by Sony. When recorded to tape, DVCAM uses wider track pitch - 15 mkm vs. 10 mkm - which reduces the chances of dropout errors. Tape is transported 50% faster, resulting in recording time reduced by one third compared to DV. Because of the wider track, 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. Another feature of DVCAM is locked audio. If several generations of copies are made on DV, the audio sync may drift. On DVCam this does not happen.^[6]

DVCPRO is a variation of DV developed by Panasonic for electronic news gathering (ENG) use, with better linear editing capabilities and robustness. Like DVCAM, it uses locked audio and 4:1:1 chroma subsampling for both 50 Hz and 60 Hz variants. Audio is available only in the 16-bit/48 kHz variant. Long Play mode is not available. When recorded to tape, DVCPRO uses 18 mkm track pitch and has additional longitudinal analog audio cue track. For DVCPRO, Panasonic developed tape with different formulation - Metal Particle instead of Metal Evaporated.

DVCPRO50, created by Panasonic for high-value ENG and digital cinema, is often described as two DV-codecs working in parallel. The DVCPRO50 standard doubles the coded video bitrate to 50 Mbit/s, cutting recording time in half compared to base DV/DVCPRO. Chroma resolution is improved by using 4:2:2 chroma sampling. The resulting picture quality is reputed to rival Digital Betacam. BBC used DVCPRO50 to film high-budget TV series, such as Space Race (2005) and Rome (2006).^[7][8]

DVCPRO HD, also known as DVCPRO100, uses four parallel codecs and a recorded video bitrate of 40-100 Mbit/s, depending on the format flavour. DVCPRO HD encodes using 4:2:2 color sampling, compared to 4:2:0 or 4:1:1 for lower-bitrate video formats. DVCPRO HD horizontally compresses recorded images to 960x720 pixels for 720p output, 1280x1080 for 1080/59.94i or 1440x1080 for 1080/50i. This horizontal compression is similar to but more significant than that of other HD formats such as HDCam, HDV, AVCHD and AVCCAM. The final DCT compression ratio of DVCPRO HD is approximately 6.7:1. To maintain compatibility with HDSDI, DVCPRO100 equipment upsamples video during playback. A camcorder using a special variable-framerate (from 4 to 60 frame/s) variant of DVCPRO HD called VariCam is also available. All these variants are backward compatible but not forward compatible. 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.

DVCPRO cassettes are always labeled with a pair of run times, the smaller of the two being the capacity for DVCPRO50. A "M" tape can hold up to 66/33 minutes of video. The color of the lid indicates the format: DVCPRO tapes have a yellow lid, longer "L" tapes made specially for DVCPRO50 have a blue lid and DVCPRO HD tapes have a red lid. The formulation of the tape is the same, and the tapes are interchangeable between formats. The running time of each tape is 1x for DVCPRO, ½x for DVCPRO 50, ½x for DVCPRO HD EX, and ¼x for DVCPRO HD, since the tape speed changes between formats. Thus a tape made 126 minutes for DVCPRO will last approximately 32 minutes in DVCPRO HD.

Connectivity

The FireWire (aka IEEE 1394) serial data transfer bus is not a part of the DV specification, but co-evolved with it. Nearly all DV cameras have an IEEE 1394 interface and analog composite video and Y/C outputs. High end DV VTRs may have additional professional outputs such as SDI, SDTI or analog component video. All DV variants have a timecode, but some older or consumer computer applications fail to take advantage of it. Some camcorders also feature a USB2 port for computer connection, but these are sometimes not capable of capturing the DV stream in full detail, and are instead used primarily for transferring certain digital data from the camcorder such as still pictures and computer-format video files (such as MPEG-4-encoded video). This carries Audio Video and Control Signals.

On computers, DV streams are usually stored in container formats such as MOV, MXF, AVI or Matroska.

Physical format

DV cassettes: DVCAM-L, DVCPRO-M, MiniDV

DV was originally designed for recording onto magnetic tape. Tape is enclosed into cassettes of four different sizes: small, medium, large and extra-large. Small cassettes, also known as "S-size" or MiniDV cassettes, were intended for amateur use, but have become accepted in professional productions as well, at least for initial acquisition if not for editing. Medium or "M-size" cassettes are used in professional Panasonic equipment only and are often called DVCPRO tapes. Large or "L-size" cassettes are used in professional equipment and are often called DVCAM tapes. Extra-large cassettes or "XL-size" have been designed for use in Panasonic equipment and are sometimes called DVCPRO XL. All DV cassettes use tape that is ¼ inch (6.35 mm) wide.

All consumer camcorders and handheld professional camcorders use small cassettes. Medium and large cassettes are used in some shoulder mount professional camcorders and in professional tape recorders. Usage of extra large cassettes is not widespread, only two models of standalone tape recorders made by Panasonic can accept it.

DV cassettes can come with a memory-in-cassette (MIC) low capacity EEPROM memory chip. Using the I²C protocol, cameras and recording decks can record any data desired onto this chip like contents list, times and dates of recordings, camera settings or video thumbnails, taken each time the record button on the camcorder is pressed. MIC functionality is optional, it is not widely used in consumer equipment. Most tapes available to consumers do not include the MIC chip.

After the DV specification was introduced, Sony retrofitted its 8-mm camcorders with DV encoding scheme, creating Digital8. This allowed recording 40 minutes of DV video onto one-hour Video8/Hi8 cassette. Digital8 did not get as widespread acceptance as MiniDV and Digital8 camcorders were discontinued by Sony in 2006.

With proliferation of tapeless systems, DV video can presently be recorded on multitude of media, including optical discs, solid state memory cards and hard disk drives. In particular, Ikegami's Editcam System can record in DVCPRO or DVCPRO50 format on a removable hard disk. Panasonic P2 devices can record DV, DVCPRO, DVCPRO50, DVCPROHD streams in an MXF wrapper. XDCAM format, developed by Sony, allows recording DVCAM video in an MXF wrapper on a ProDATA disc. XDCAM EX format, a variation of XDCAM, allows recording DVCAM video in an MXF wrapper onto SxS cards.

Application software support

Most DV players, editors and encoders only support the basic DV format, but not its professional versions. 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 AVI container files. The DV meta-information is preserved in both file types.

Most Windows video software only supports DV packed into AVI containers, as they use Microsoft's avifile.dll, which only supports reading avi files. A few notable exceptions exist:

• Apple Inc.'s QuickTime Player: QuickTime by default only decodes DV to half of the resolution to preserve processing power for editing capabilities. However, in the "Pro" version the setting "High Quality" under "Show Movie Properties" enables full resolution playback.
• DVMP Basic & DVMP Pro: full decoding quality. Plays AVI (inc DVCPRO25 and DVCAM) and.dv files. Also displays the DV meta-information (e.g. timecode, date/time, f-stop, shutter speed, gain, white balance etc)
• The VLC media player (Free software): full decoding quality
• MPlayer (also with GUI under Windows and Mac OS X): full decoding quality
• muvee Technologies autoProducer 4.0: Allows editing using FireWire IEEE 1394
• Quasar DV codec (libdv) - open source DV codec for Linux

Type 1 and Type 2 DV AVI files

There are two types of DV-AVI files:

• Type 1: The multiplexed Audio-Video is kept in its original multiplexing and saved together into the Video section of the AVI file
  • Does not waste much space (audio is saved uncompressed, but even uncompressed audio is tiny compared to the video part of DV), but Windows applications based on the VfW API do not support it.
• Type 2: Like type 1, but audio is also saved as an additional audio stream into the file.
  • Supported by VfW applications, at the price of little increased file size.

Type 1 is actually the newer of the two types. Microsoft made the "type" designations, and decided to name their older VfW-compatible version "Type 2", which only furthered confusion about the two types. In the late 1990s through early 2000s, most professional-level DV software, including non-linear editing programs, only supported Type 1. One notable exception was Adobe Premiere, which only supported Type 2. High-end FireWire controllers usually captured to Type 1 only, while "consumer" level controllers usually captured to Type 2 only. Software is and was available for converting Type 1 AVIs to Type 2, and vice-versa, but this is a time-consuming process.

Many current FireWire controllers still only capture to one or the other type. However, almost all current DV software supports both Type 1 and Type 2 editing and rendering, including Adobe Premiere. Thus, many of today's users are unaware of the fact that there are two types of DV AVI files. In any event, the debate continues as to which – Type 1 or Type 2 – if either, is better.

Mixing tapes from different manufacturers

There is controversy over whether or not using tapes from different manufacturers can lead to dropouts.^[9][10][11] The problem theoretically occurs when incompatible lubricants on tapes of different types combine to become tacky and deposit on tape heads. This problem was supposedly fixed in 1997 when manufacturers reformulated their lubricants, but users still report problems several years later. Much of the evidence relating to this issue is anecdotal or hearsay. In one case, a representative of a manufacturer (unintentionally) provided incorrect information about their tape products, stating that one of their tape lines used "wet" lubricant instead of "dry" lubricant.^[12] The issue is complicated by OEM arrangements: a single manufacturer may make tape for several different brands, and a brand may switch manufacturers.

It is unclear whether or not this issue is still relevant, but as a general rule many DV experts recommend sticking with one brand of tape^{[citation needed]}.

See also

• Digital8
• Camcorder
• MPEG
• Video quality

Formats

• HDV and its variant, ProHD
• MicroMV
• DVD

References

External links

• DVworkshops.com Free DV Video Handbook. Cameras, Lights and Interview techniques
• Adam Wilt's DV page with in-depth technical information
• Tips and training for working with DVCPROHD, HDV and DV.
• Digital Video Information Network messageboards
• Technical Documentation on the storage of DV data in AVI files: short and in detail