Digital Video (DV) is a digital video format created by Sony, JVC, Panasonic and other video camera procuers and launched in 1995, and, in 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, a standard interface for transfer to non-linear editing systems (IEEE 1394, also known as FireWire), 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.
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’ 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. 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. 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.
Before arriving at the codec compression stage, light energy hitting the sensor is transduced into analog electrical signals. These signals are then converted into digital signal by an analog to digital converter (ADC or A/D). This signal is then processed by a digital signal processor (DSP) or custom ASIC and undergoes the following processes:
Processing of raw input into (linear) RGB signals: For Bayer pattern-based sensors (i.e. sensors utilizing a single CCD or CMOS and color filters), the raw input has to be demosaiced. For Foveon-based designs, the signal has to be processed to remove cross-talk between the color layers. In pixel-shifted 3CCD designs, a process somewhat similar to de-mosaicing is applied to extract full resolution from the sensor.
Matrix (for colorimetry purposes): The digital values are matrixed to tweak the camera's color response to improve color accuracy and to make the values appropriate for the target colorimetry (SMPTE C, Rec. 709, or EBU phosphor chromaticities). For performance reasons, this matrix may be applied after gamma correction and combined with the matrix that converts R'G'B' to Y'CbCr.
Electronic white balance may be applied in this matrix, or in the matrix operation applied after gamma correction.
Gamma correction: Gamma correction is applied to the linear digital signal, following the Rec. 601 transfer function (a power function of 1/0.45). Note that this increases the quantization error from before.
Matrix (R'G'B' to Y'CbCr conversion): This matrix converts the gamma-corrected R'G'B' values to Y'CbCr color space. Y'CbCr color space facilitates chroma subsampling. This operation introduces yet more quantization error, in large part due to a difference in the scale factors between the Y' and Cb and Cr components.
Chroma Subsampling: Since human vision has greater acuity for luminance than color, performance can be optimized by devoting greater bandwidth to luminance than color. Chroma subsampling approximates this by converting R'G'B' values into Y'CbCr color space. The Cb and Cr color difference components are stored at a lower resolution than the Y' (luma) component.
Sharpening is often used to counteract the effect of optical low pass filtering. Sharpening can be implemented via finite impulse response filters.
Low chroma resolution is a reason why DV is sometimes avoided in applications where chroma-key will be used. Nevertheless, advances in keying software (i.e. the combination of chroma keying with different keying techniques, chroma interpolation) allows for reasonable quality keys from DV material.
The DV format uses "L-size" cassettes, while MiniDV cassettes are called "S-size". Both MiniDV and DV tapes can come with a low capacity embedded memory chip (MIC) (most commonly, a scant 4 Kbit for MiniDV cassettes, but the system supports up to 16 Kbit). This embedded memory can be used to quickly sample stills from edit points (for example, each time the record button on the camcorder is pressed when filming, a new "scene" timecode is entered into memory). DVCPRO has no "S-size", but an additional "M-size" as well as an "XL-size" for use with DVCPRO HD VTRs. All DV variants use a tape that is ¼ inch (6.35 mm) wide.
The "L" cassette is about 120 × 90 × 12 mm and can record up to 4.6 hours of video (6.9 hours in EP/LP). The better known MiniDV "S" cassettes , 65 × 48 × 12 mm and hold either 60 or 90 minutes of video (13 or 19.5 GB) depending on whether the video is recorded at Standard Play (SP) or Extended Play (sometimes called Long Play) (EP/LP). 80 minute tapes that use thinner tape are also available and can record 120 minutes of video in EP/LP mode. The tapes sell for as little as US$2.50 each in quantity as of 2008. DV on SP has a helical scan track width of 10 micrometres, while EP uses a track width of only 6.7 micrometres. Since the tolerances are much tighter, the recorded tape may not play back properly or at all on other devices.
Software currently available for ordinary home computers which allows users to record any sort of computer data on MiniDV cassettes using common DV decks or camcorders. Though originally intended for the consumer market as a high-quality replacement for VHS, L-size DV cassettes are largely nonexistent in the consumer market, and are generally used only in professional settings. Even in professional markets, most DV camcorders support only MiniDV, though many professional DV VTRs support both sizes of tape.
Because of wider track DVCAM has the ability to do a frame accurate insert tape edit. DV will 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.
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. BBC preferred DVCPRO50 camcorders over HDCAM cameras to film popular TV series, such as Space Race (2005) and Rome (2006).
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.
Both families are compliant with the DV standard. For detailed information see datasheet: Serial I²C bus EEPROM (STMicroelectronics).
MIC functionality is not widely used on the consumer level; most tapes available to consumers do not even include the chip, which adds substantially to the price of each cassette. Most consumer equipment includes the circuitry to read and write to the chip even though it is rarely used.
Digital video dates back to 1986, with the creation of the uncompressed D-1 format for professional use (although several professional video manufacturers such as Sony, Ampex, RCA, and Bosch had experimentally developed prototype digital video recorders dating back to the mid-to-late 1970s).
Sony has several digital specifications for professional use, the most common for standard definition use being Digital Betacam, a distant descendant of the Betamax products of the 1970s thru 1990s from which it received only some mechanical aspects, notably the form of the cassette. (Betamax itself descended from Sony's U-Matic ¾ inch videocassette system.) JVC's D-9 format (also known as Digital-S) is very similar to DVCPRO50, but records on videocassettes in the S-VHS form factor. (NOTE: D-9 is not to be confused with D-VHS, which uses MPEG-2 compression at a significantly lower bitrate.)
The Digital8 standard uses the DV codec, but replaces the recording medium with the older Hi8 videocassette. Digital8 theoretically offers DV's digital quality, without sacrificing playback of existing analog Video8/Hi8 recordings. However, in practice the maximum quality of the format is unlikely to be achieved, since Digital8 is largely confined to low-end consumer camcorders. It is also a semi-proprietary format, being manufactured exclusively by Sony (although Hitachi also made Digital8 camcorders briefly).
DVD was originally created as a distribution format, but recordable DVDs quickly became available. Camcorders using miniDVD media are fairly common on the consumer level, but due to difficulties with editing the MPEG-2 data stream, they are not widely used in professional settings.
Sony also made a format called MicroMV, which stored MPEG-2 video on a matchbox-sized tape. Due to lack of platform support and the difficulties of editing MPEG-2 video, MicroMV never became popular and was discontinued by 2005.
Sony's XDCAM format allows recording of MPEG IMX, DVCAM and low resolution streams in an MXF wrapper on a Sony ProDATA disc, an optical medium similar to a Blu-ray Disc. Sony has also, in cooperation with Panasonic, created AVCHD, a medium-independent codec for consumer high definition video; it is currently used on camcorders containing hard disks, SD cards and DVD-R drives for storage.
Type 1 and Type 2 DV AVI files
There are two types of DV-AVI files:
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.
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.