Digital Video (DV) Compression Technology
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Digital Video (DV) is a digital video format launched in 1994, and, in its smaller tape form factor MiniDV, has since become a standard for home and semiprofessional video production; it is sometimes used for professional purposes as well, such as filmmaking and electronic news gathering. 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, a standard interface for transfer to non-linear editing systems (FireWire, also known as IEEE 1394), and good video quality, especially compared to earlier consumer analog formats such as 8 mm, Hi8 and VHS-C.
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.
DVCPRO
Panasonic specifically created the DVCPRO family for electronic news gathering (ENG) use, with better linear editing capabilities and robustness. It has an even greater track width of 18 micrometres and uses another tape type (Metal Particle instead of Metal Evaporated). Additionally, the tape has a longitudinal analog audio cue track. Audio is only available in the 16 bit/48 kHz variant, there is no EP mode, and DVCPRO always uses 4:1:1 color subsampling (even in PAL mode). Apart from that, standard DVCPRO (also known as DVCPRO25) is otherwise identical to DV at a bitstream level. However, unlike Sony, Panasonic chose to promote its DV variant for professional high-end applications.
DVCPRO50 is often described as two DV-codecs in parallel. The DVCPRO50 standard doubles the coded video bitrate from 25 Mbit/s to 50 Mbit/s, and uses 4:2:2 chroma subsampling instead of 4:1:1. DVCPRO50 was created for high-value ENG compatibility. The higher datarate cuts recording time in half (compared to DVCPRO25), but the resulting picture quality is reputed to rival Digital Betacam.
DVCPRO HD, also known as DVCPRO100, uses four parallel codecs and a coded video bitrate of approximately 100 Mbit/s, depending on the format flavour. DVCPRO HD encodes using 4:2:2 color sampling. DVCPRO HD prefilters the 720p image from the DSP to a recorded size of 960x720, and 1080i is prefiltered to 1280x1080 for 59.94i and 1440x1080 for 50i. This is a common technique, utilized in most tape-based HD formats such as HDCam and HDV. The final DCT compression ratio 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. There is also a DVCPRO HD EX format, which runs the tape at slower speed, resulting in twice as long recording times. 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.
