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.
Overview
DV uses discrete cosine transform (DCT) to compress every video frame individually. Before applying DCT compression, some color information is removed from original video using chroma subsampling 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, though advances in chroma keying techniques and software made producing quality keys from DV material possible.
The sampling raster of the baseline DV video is the same as that of the ITU-R Rec.601 with 720 pixels per line for both 4:3 and 16:9 frame aspect ratios, which results in different pixel aspect ratios for fullscreen and widescreen video. The 60 Hz system has 480 lines, while the 50 Hz system has 576 lines in a frame.
The video, the corresponding audio and metadata are packaged into 80-byte Digital Interface Format (DIF) blocks which are multiplexed in a 150-block sequence. DIF blocks are the basic units of DV streams and can be stored as files in raw form or wrapped in such file formats as AVI, QuickTime and MXF. One video frame is formed from either 10 or 12 such sequences, depending on scanning rate, which results in the data rate of about 25 Mbit/s. When written to tape, each sequence correspond to one complete track.
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 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 , 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.
DVCAM
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 was introduced by Panasonic in 1997 for high-value 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. The resulting picture quality is reputed to rival Digital Betacam.
DVCPRO50 is used in many productions where high definition is not required. For example, BBC used DVCPRO50 to film high-budget TV series, such as Space Race (2005) and Rome (2006).
DVCPRO Progressive
DVCPRO Progressive was introduced by Panasonic for news gathering, sports journalism and digital cinema. Offering 480 or 576 lines of progressive scan recording with 4:2:0 chroma subsampling and four 16-bit 48 kHz PCM audio channels, 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). DVCPRO Progressive uses 4:2:0 chroma sampling when used in progressive modes, and delivers full 50 frames/s or 60 frames/s recording.
The format has been superseded with DVCPRO HD.
DVCPRO HD
DVCPRO HD , also known as DVCPRO100 is a high definition format that can be thought of as four DV codecs that work in parallel. Video data rate can be as low as 40 Mbit/s for 24 frame/s mode or as high as 100 Mbit/s for 50/60 frames/s. 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 compression is similar to many other HD formats. To maintain compatibility with HDSDI, DVCPRO100 equipment upsamples video during playback.
Variable framerate (from 4 to 60 frame/s) is 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-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 and do not use small cassettes. Handheld cameras that are capable of DVCPRO HD recording use expensive solid-state P2 memory cards. DVCPRO HD has never become a consumer high definition format and lost this market to HDV and AVCHD.
Progressive recording
DV has been designed as an interlaced video recording standard. After DV became a popular format for digital cinema, it became apparent that filmout process required blending of fields, which caused loss of resolution and exhibited interlace artifacts that were not noticeable on an interlaced television set. This gave rise to camcorders capable of progressive-scan acquisition.
None of DV variants except for DVCPRO Progressive supports native progressive recording, therefore progressively acquired video is recorded within interlaced video stream using pulldown. The same technique is used in television industry to broadcast movies.
DV camcorders for 60 Hz market that are capable of shooting progressive video, record 24-frames/s video using 2-3 pulldown, and 30-frames/s video using 2-2 pulldown. DV camcorders for 50 Hz market, capable of shooting progressive video, record 25-frames/s video using 2-2 pulldown.
Progressive video can be recorded with interlaced delivery in mind, in which case high-frequency information between fields is blend
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