Technical overview of digital video systems
- Creighton Barrett
- Ann Terese MacDonald (Unlicensed)
Introduction
- This page provides a technical overview of digital video systems.
- This overview supplements information about specific digital videocassette formats described in the master list of physical objects.
Development of digital video systems
| Date | Event | Reference |
|---|---|---|
| 1951 | Ampex Corporation develops video tape recorder that captured live images from television cameras and converting the information into electrical impulses that could be stored on tape. | Phillips, 2016 |
| 1956 | Ampex and RCA release 2 inch quad videotape format. | Museum of Obsolete Media |
| 1971 | Sony releases first U-matic video cassette recorder (VCR). | Museum of Obsolete Media |
| 1975 | Sony releases Betamax format. Betamax was the first consumer technology that allowed users to record television broadcasts and view videocassettes at home. The format was obsolete by the 1980s. | Museum of Obsolete Media |
| 1976 | Victor Company releases VHS (Video Home System) format. It was created in Japan by the Victor Company. VHS is an analog recording videocassette, encoded in FM on a magnetic tape. VHS sales declined through the 1990s and early 2000s and mainstream sales of cassettes and players ceased ca. 2008. | Black, 2013 |
| 1984 | Sony launches HDVS equipment with HDC-100 camera, HDV-1000 video tape recorder, HDT-1000 processor/TBC, and HDS-1000 video switcher | VideOlson |
| 1985 | Sony launches Video8. At the time, the market was dominated by VHS-C and Betamax formats. | Museum of Obsolete Media |
| 1989 | Avid releases Avid/1 non-linear video editing system based on Macintosh II computers with special hardware and software installed by Avid. | Escobar, 2018 |
| 1993 | Sony introduces Digital Betacam format as a replacement for the analog Betacam SP format. | Texas Commission on the Arts. Videotape assessment and identification guide (2004): 27. |
| 1994 | Apple releases FireWire cable, patented as IEEE 1394 | Open WIKI |
| 1995 | DV format is launched by a consortium of leading producers of video camera recorders. | Jennings, 1997 |
| 1995 | Sony releases the 3-CCD DCR-VX1000 (U.S. MSRP $4,199) and the single-CCD Sony DCR-VX700 (MSRP $2,999). The camcorders supported the IEEE 1394 FireWire connector and enabled direct digital output to non-linear editing (NLE) systems. | Jennings, 1999 |
| 1995 | Panasonic introduces the DVCPRO format. DVCPRO is based on the DV format. | Jennings, 1997 |
| 1996 | Sony and JVC introduce MiniDV format. JVC and Sony released in 1996 two highly-miniaturized DV camcorders to the U.S. market. The $3,000+ Sony DCR-PC7 sports a 2.5-inch fold-out LCD monitor, in addition to a color viewfinder, and offers an IEEE-1394 connector. In January 1997, Matsushita released details of two miniature DV camcorders, one of which has a 4-inch LCD monitor. Both of the new Panasonic camcorders have IEEE-1394 connectors. Sharp's 1996 DV entry featured a large LCD display, but neither the JVC or Sharp models include IEEE-1394 capability. Sony's DHR-1000 DVCR is scheduled for widespread U.S. availability in Spring 1997. | Jennings, 1997 |
| 1996 | Sony introduces DVCAM format. | VideOlson |
| 1997 | Panasonic introduces DVCPRO50 format. | Museum of Obsolete Media |
| 1998 | European Broadcasting Union (EBU) releases technical review EBU/SMPTE Task Force for Harmonized Standards for the Exchange of Programme Material as Bitstreams. The report suggests that:
| Laven & Meyer, 1998 |
| 1998 | IEC 61834-2 is published. | International Electrotechnical Commission |
| 1999 | Sony introduces Digital8 format. Digital8 records video onto Hi8 tape using the DV codec. | Museum of Obsolete Media |
| 1999 | SMPTE 314M (525/60i and 625/50i) is published (covers both DVCAM and DVCPRO) | |
| 2001 | Sony introduces Betacam IMX format to compete with MPEG-2 formats. | VideOlson |
| 2001 | MPEG-4 format is launched. | Museum of Obsolete Media |
| 2002 | SMPTE 370M (1080/60i, 1080/50i, and 720/60p) is published (covers DVCAM HD) | |
| 2003 | HDV format is launched. | Museum of Obsolete Media |
| 2016 | Sony announced it was ceasing production of 1/2 inch video players and recorders. | Museum of obsolete media: digital betacam |
Select technical standards
Digital video systems are designed in accordance with an assortment of international technical standards. Key general standards include:
International Telecommunication Union (ITU) recommendation BT.601-7 (approved March 2011) Studio encoding parameters of digital television for standard 4:3 and wide-screen 16:9 aspect ratios.
International Telecommunication Union (ITU) recommendation BT.709-6 (approved June 2015) Parameter values for the HDTV standards for production and international programme exchange.
25 Mbps: International Electrotechnical Commission (IEC) standard 61834-5 Helical-scan digital videocassette recording system using 6.35 mm magnetic tape for consumer use (525-60, 625-50, 1125-60, 1250-50 systems).
Data Transfer
- IEEE standard 1394:2008 for a high-performance serial bus (revision of IEEE standard 1934:1995).
Physical composition of digital videocassettes
Videocassettes are a physical format that can store analog or digital video signals. This information is stored on a magnetic tape, which is is housed within a plastic cassette or cartridge.
Videotape consists of magnetized particles embedded on a polyester tape carrier. The tape carrier is usually made up of several layers, including the backcoat, basefilm and binder. The magnetic coating adheres to the binder, creating the top layer of the tape.
Image source
Layer structure of DVCPRO tape. DVCPRO: Digital linkage to the 21st century, 2nd edition. Panasonic.
| Layer | Description |
|---|---|
| Backcoat | The carbon based backcoat layer reduces tape friction and prevents the build up of electro-static charges. The backcoat effectively merges with other tape layers to create a uniform and stable tape pack that is less prone to distortion. |
| Basefilm | The base layer acts as a substrate or carrier to support the tape during playback. Polyester (also known as Mylar or PET) is the most common material used to create the basefilm, however tapes produced between the 1950s and 1970s may use acetate or PVC as a base layer. |
| Binder | The binding layer supports the magnetic coating and adheres the magnetic particles to the basefilm. The binder also creates a smooth surface to ensure the tape travels through playback equipment with ease. The binder may be composed of various polymers, such as cellulose nitrate, chlorine bearing vinyls, and sundry epoxy and acrylic resins. Polyester urethane elastomer is a common binder used for magnetic video tape. The binder is often the first layer to show signs of degradation. |
| Magnetic coating | The top layer of the tape is made up of magnetic particles mixed with binder, lubricant, head cleaning agent, surfactant, and other chemicals. The magnetic coating is approximately 200 micro-inches thick and the particles range from 10 to 20 micro-inches in length. Iron oxides, such as Ferric oxide (FEE2O3), are most commonly used because they are relatively stable and create uniform magnetic particles. Tapes produced using this method are referred to as metal particulate (MP) tapes. Metal evaporate (ME) tape (also known as thin film magnetic tape) was originally developed for the Hi-8 format in 1989. ME tapes do not use a binder to adhere the magnetic particles to the tape. Instead, the magnetic material is vaporized and applied to the tape inside of a vacuum chamber. A thin protective coating is used to seal the magnetic layer. Although this process creates a densely packed film, the thin coating is more susceptible to damage. |
Technical characteristics of digital video
Digital video is defined by the following characteristics:
- Data rate
- Bit depth
- Color sample rate
- Resolution
- Compression
- Codec
- File format (i.e., wrapper)
Data rate
Data rate (also referred to as bitrate) represents the amount of data encoded for a unit of time. Data rates for digital video can be measured in megabits per second (mb/sec) or megabytes per second (MB/sec). Divide value by eight to convert mb/sec to MB/sec (8 bit = 1 Byte).
Kilobits per second (Kbps, kb/sec, kb/s) and kilobytes per second (KB/sec, KB/s) provide another way to measure data transfer and storage. Example storage estimates: 5000 Kbps = 625 KB/sec.
Image source
Kong, David. "The Simple Formula to Calculate Video Bitrates." Frame.io Insider. Accessed January 14, 2021.
Bit depth
Indicates the number of bits used to represent each colour channel (red, green and blue) for each pixel in a digital image or video frame. As the bit depth increases, so does the number of colours that can be displayed. Increasing the bit depth also increases the file size and storage requirements because more data is being recorded. The most common bit depths for digital video are 8 bit, 10 bit and 12 bit.
| Bit Depth | R/G/B | Total Colours | Notes |
|---|---|---|---|
| 8 Bit | 256 | 16,777,216 | Colour banding can occur in areas of gradation if playback mechanism has a bit depth greater than 8 Bit |
| 10 Bit | 1024 | 1,073,741,824 | Increased dynamic range (more shades in dark and light areas) will be apparent when paired with 10 Bit playback mechanism |
| 12 Bit | 4096 | 68,719,476,736 | Provides greater dynamic range and favoured in digital postproduction and processing |
Image source
Chart showing the possible colors in 8 bit, 10 bit and 12 bit video. Understanding bit-depth and color rendition for video. Accessed December 10, 2020.
Color sample rate
Y'CbCr Color Model
Y'CbCr is a type of digital colour sampling that is derived from the analog Y'UV model. In Y'CbCr the colour information (Red, Green and Blue) is encoded into a luminance value (Y) and two croma components (Cb, Cr). In the Y'CbCr model, colour information can be downsampled without altering image brightness because the luminance value and chroma components are encoded separately. Therefore data storage requirements can be decreased, without reducing overall image quality.
Image source
Fig.04 - RGB/YCbCr Color Sampling. Video Basics. Accessed January 5, 2021.
Chroma subsampling
In chroma subsampling, the colour components in a video signal are sampled at a lower rate than the luminance value. The human visual system is less responsive to colour than brightness, so reductions in colour information are not perceived by the human eye. Video signals that have a lower colour resolution have a lower bandwidth and require less storage space. Chroma Subsampling specifications are expressed as a three digit ratio (4:n:n) where 4 represents the sampling rate of the luminance value (Y) and n:n represents the two chroma components (Cr:Cb).
| Sample Rate | Description |
|---|---|
| 4:4:4 | All values are sampled at the same rate |
| 4:2:2 | Cb and Cr are sampled at half the horizontal resolution of Y |
| 4:1:1 | Cb and Cr are sampled at one quarter the horizontal resolution of Y |
| 4:2:0 | Cb and Cr are sampled at half the vertical resolution of Y |
Image source
Fig.06 - Examples of different color sampling formats. Video Basics. Accessed January 5, 2021.
Resolution
Video resolution refers to the number of pixels that are displayed in the image or frame. Video pixels form a grid of vertical and horizontal lines and video resolution measures the number of rows of pixels by the number of columns (Example: 720x576, 1280x720, 1920x1080).
The horizontal and vertical pixel dimensions of the format determine the video frame size and aspect ratio. Aspect ratio refers to the ratio of horizontal to vertical dimensions of the image or video frame. Aspect ratios can be written as absolute dimensions (4x3), ratios (4:3) or decimal equivalents (1.33:1).
| Frame size | Aspect ratio | Description (common formats) |
|---|---|---|
| 1920x1080 | 16:9 | 1080p/i |
| 1440x1080 | 16x9 | 1080i (Most HDV use this format) |
| 1280x720 | 16x9 | 720p |
| 852x480 | 16x9 | 480p |
| 720x480 | 4:3 | DV NTSC (when the pixels are square it is actually 3:2) |
| 720x480 | 16:9* | DV NTSC / Anamorphic* / Wide Screen (non square pixles) |
| 720x576 | 5:4 | DV PAL |
| 640x480 | 4:3 | a ration suitable for square size pixle multimeida video. |
| 640x360 | 16:9 | a ration suitable for square size pixle multimeida thats widescreen. |
| 480x360 | 4:3 | Multimedia large (480x360 : 75%(640x480)) |
| 480x270 | 16:9 | Multimedia Large (similar to Apple's large move trailer standard 480x272) (480x270 : 75%(640x360)) |
| 320x240 | 4:3 | Multimedia Large |
| 320x180 | 16:9 | Multimedia Large / Wide Screen |
| 240x180 | 4:3 | Multimedia Small |
| 160x120 | 4:3 | Thumbnail |
| 1600x1200 | 4:3 | Computer Display |
| 1280x1024 | 4:3 | Computer Display |
| 1152x870 | 4:3 | Computer Display |
| 1024x768 | 4:3 | Computer Display |
| 800x600 | 4:3 | Computer Display |
Compression
Digital video files are generally large and contain too much information to be efficiently processed, transferred or stored. Compression decreases the size of a video file by reducing the number of bits (where bit rate is the amount of data being processed per unit of time during playback or transfer). Files with a lower bit rate require less storage space, compared to uncompressed files. Video codecs are used to compress and decompress video files. For example, DV uses a intra-frame discrete cosine transform (DCT) based compression codec.
Codec
A video codec (enCOder/DECoder) is a type of software or hardware that compresses and decompresses a digital video signal. Codecs compress data for storage or file transfer and then decompress the video file for playback and editing.
There are two main types of codecs– lossy codecs and lossless codecs.
- Lossy codecs: Can significantly reduce file size, however some information from the original video file is lost during compression and may result in reduced image quality. Repeated use of lossy compression can further distort the video as more information is lost during each conversion. A lossy codec should only be used once, as a final step after the video has been fully edited and is ready for sharing. This approach is best for video files that will be shared online or viewed on a smartphone.
- Lossless codecs: Can compress video files without affecting playback quality. Lossless codecs use mathematical algorithms to preserve the original video information during compression. When the video file is decompressed it is fully restored to the original size and quality. Depending on workflows and storage capacities, lossless compression may produce video files that are too large to manage.
Image source
"Video Streaming Codecs & Container Formats: All you Need to Know." Muvi. August 7, 2020.
Most codecs in use today correspond with one of two international standards for video coding– the SO/IEC Motion Picture Experts Group (MPEG) family or the video coding experts group (VCEG) H.26x family. Codecs that employ different standards are not normally compatible. For example, the H.264 encoder will not work with the MPEG4-4, Part 2 decoder. Software and hardware can enable greater compatibility by implementing many different encoders and decoders.
MPEG Video Coding Standards
H.26X Video Coding Standards
Image source
Table 1 - MPEG family & Table 2 - H.26x line of standards. Historical timeline of video coding standards and formats. Accessed January 21, 2020.
| Common Video Codecs | |
|---|---|
| DV (Digital Video) |
|
| MPEG-2 |
|
| Divx (.divx) |
|
| Motion JPEG (MJPEG) |
|
| Windows Media Video (.wmv) |
|
| FFV1 (FF video codec 1) |
|
Table source
Saavedra i Bendito, P. "The Digital Video Archive." International Council on Archives. April, 2014.
File format (i.e., wrapper/container)
A wrapper packages the coded essence and metadata of a video file together into a file format. A wrapper provides a storage environment for content and describes the structure of the content.
Overhead – data about the construction of the wrapper, including flags, headers, separators, byte counts, checksums, etc.
Empty wrapper – overhead only
Content – metadata plus essence
Full wrapper – overhead plus metadata plus essence
Image source
Schematic view of wrappers in use. Final Report of the EBU / SMPTE Task Force for Harmonized Standards for the Exchange of Television Programme Material as Bitstreams, page 55 (1998).
| Common Wrapper/Container Formats | |
|---|---|
| Advanced Authoring Format (AAF) |
|
| Advanced System Format (.asf) |
|
| Audio Video Interleave (.avi) |
|
| Quicktime (.mov, .qt) |
|
| Motion JPEG 2000 (MJ2 o MJP2) |
|
| MPEG-4 |
|
| Material Exchange Format (MXF) |
|
| Flash Video (.flv) |
|
| Ogg (,ogg) |
|
| Matroska (.mkv) |
|
Table source
Saavedra i Bendito, P. "The Digital Video Archive." International Council on Archives. April, 2014.
Digital Video (DV) standard
DV is a term that is used to describe a specific digital video encoding standard and the physical formats (i.e., videocassettes) that utilize this standard. The original DV encoding standard IEC 61834 was developed by a consortium of electronics manufacturers (Sony, JVC, and Panasonic) and was released for consumer use in 1995. DV encoding standards for professional use were also published as SMPTE 314M and SMPTE 370M.
According to the DV encoding standard, video must be recorded using 6.35 mm (1/4 inch) magnetic videotape. DV videotape can be housed in small (66 x 48 x 12.2 mm), medium (97.5 × 64.5 × 14.6 mm), large (125.1 x 78 x 14.6 mm) or extra-large (172 x 102 x 14.6 mm) videocassettes.
In 1996, Sony and JVC released consumer video tape recorders (VTRs) that supported a miniaturized DV videocassette known as MiniDV. Some VTRs available during this time were also compatible with standard DV (also called DVC) videocassettes. DVC cassettes are larger and can record more video than MiniDV cassettes (3.5 - 4 hours of compared to 60 minutes), however MiniDV cassettes were much more popular among consumers.
Following this, more variations of the DV format were introduced for consumer and professional markets including DVCAM, DVCPRO, DVCPRO50 and DVCPRO HD. As a general term, DV now refers to the family of video encoding specifications, camcorders, VCRs, and videocassettes that are based on the original DV video recording specification.
Technically any of the DV format variations can be recorded onto any DV cassette, depending on the recording equipment that is used. This is because all variations are based on the original DV encoding standard. However, each DV variation has a different recording speed, so the formats may not be backwards compatible. For example, a DVCPRO recording cannot be played on standard DV playback equipment. DV cassettes are generally labeled by manufacturers to indicate the intended encoding variation.
Image source
DV Cassettes. The Free Dictionary by Farlex.
Technical characteristics of DV
DV uses an intra-frame discrete cosine transform (DCT) based compression codec called I-MPEG. This means that each frame is compressed individually, which makes DV a good format for video editing. DV also uses the Firewire (IEEE 1394) interface standard to transfer data between cameras and editing equipment.
DV track configuration
Digital video captured in any of the DV-based recording modes has four sectors:
- insert and track information (ITI) sector
- audio sector
- video sector
- subcode sector
Image source
Doyle, Bob. Inside the DV Spec. Accessed January 15, 2021.
DV storage requirements
The following reference tables can also be used to determine approximate DV storage capacities by file size or recording time time.
| DV Storage Capacities by Size | |
|---|---|
| File Size | Length of Recording |
| 10 GB | 45 minutes |
| 20 GB | 1.5 hours |
| 40 GB | 3 hours |
| 60 GB | 4.5 hours |
| 80 GB | 6 hours |
| 100 GB | 7.5 hours |
| 120 GB | 9 hours |
| 180 GB | 14 hours |
| 200 GB | 15.5 hours |
| 400 GB | 31 hours |
| 500 GB (0.5 TB) | 39 hours |
| 1000 (1 TB) | 79 hours |
| 10 TB | 793 hours |
| 100 TB | 7,936 hours |
| 1000 TB (PB) | 79,365 hours |
| DV Storage Capacities by Time | |
|---|---|
| Length of Recording | File Size |
| 5 minutes | 1 GB |
| 10 minutes | 2.1 GB |
| 15 minutes | 3.1 GB |
| 30 minutes | 6.3 GB |
| 1 hour | 12.6 GB |
| 2 hours | 25.3 GB |
| 3 hours | 37.9 GB |
| 4 hours | 50.6 GB |
| 5 hours | 63.2 GB |
| 10 hours | 126.5 GB |
| 25 hours | 316 GB |
| 50 hours | 632 GB |
| 75 hours | 949 GB |
| 100 hours | 1.26 TB |
| 250 hours | 3.16 TB |
| 1000 hours | 12.6 TB |
Table source
Smith, Cheyenne T. "DV and audio storage requirements." The University of Texas at Austin. Last modified October 29, 2010.
Related resources
- Section 9.0 - Outsourced digitization of audiovisual items
- Appendix C - Technical specifications for moving images
Further reading
Visit the Archives Learning Community for further reading on /wiki/spaces/ALC/pages/1891631115.
References
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Nielsen, Rebecca. "Media Recognition: DV Part 1." Bodleian Libraries. March 26, 2012.
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Poyton, Charles. "Basic Principles." In A Technical Introduction to Digital Video, 1-31. New York; Chichester: John Wiley & Sons, 1996.
Saavedra i Bendito, P. "The Digital Video Archive." International Council on Archives. April, 2014.
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"Term: Bit depth (image)." Federal Agencies Digital Guidelines Initiative. Accessed January 5, 2021.
"Video Basics." Biamp Systems. June 21, 2019.
"Video Codec." PCMag Digital Group. Accessed January 5, 2021.
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Wagner, Brian. "Lossless Video Compression: What is it and Why Should I Care?" Archival Works. December 6, 2019.
WDVA. "Do DV Formats Mystify You?" 2004.
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Version history
| Version | Date | Author(s) | Version Notes |
|---|---|---|---|
| 1.0 | February 19, 2021 | Ann Terese MacDonald and Creighton Barrett | Prepared as part of a 2020 Young Canada Works Building Careers in Heritage Internship. |