DV is a format for the digital recording and playing back of digital video. The DV codec was launched in 1995 with joint efforts of leading producers of video camcorders.
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 is an intraframe video compression scheme, which uses the discrete cosine transform (DCT) to compress video on a frame-by-frame basis. Audio is stored uncompressed.
Closely following ITU-R Rec. 601 standard, DV video employs interlaced video 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 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.
DVCPRO, also known as DVCPRO25, is a variation of DV developed by Panasonic and introduced in 1995 for use in electronic news gathering (ENG).
Unlike baseline DV, DVCPRO uses locked audio and 4:1:1 chroma subsampling for both 50 Hz and 60 Hz variants to reduce generation loss. Audio is available only in the 16-bit/48 kHz variant.
When recorded to tape, DVCPRO uses wider track pitch - 18 μm vs. 10 μm of baseline DV, which reduces the chances of dropout errors when video is recorded to tape. Two extra longitudinal tracks provide 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. .
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 (2.8cm/s) compared to DV (1.8cm/s), 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 was introduced by Panasonic in 1997 for high-value electronic news gathering (ENG) 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, cutting recording time in half compared to base DVCPRO. Chroma resolution is improved by using 4:2:2 chroma sampling.
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.
DVCPRO HD, also known as DVCPRO 100 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, DVCPRO 100 equipment upsamples video during playback.
Variable framerates (from 4 to 60 frame/s) are available on VariCam camcorders. DVCPRO HD equipment is backward compatible 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 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.
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