Digital Videotape Machines - history
No survey of videotape technology would be complete without a discussion of digital videotape. One of the severe limiting factors with analog videotape systems was that you could copy the tape only a limited number of times before noise and distortion would seriously degrade the picture. The best practical analog system was 1" type C, which could give you nine Generations (Copies or dubs) before picture impairments were objectionable. (The IVC 9000 format was claimed by some to be able to go 29 generations, but that format died when IVC went bankrupt developing the machine. Considered the finest analog VTR format ever developed, only 60 machines were ever made. Yet, 'Rowan and Martin's Laugh In' and 'Electric Company' were two major shows produced using the format.)
Just like the compact disc, it was found that if you could digitize video and record it on tape as data, there would be no loss in picture quality no matter how many times the tape was copied (Provided you stayed digital between copies). First introduced in 1987, with the Sony DVR-1000, digital videotape quickly caught on. The DVR-1000 was a component digital recorder that provided absolutely, positively no-compromise pictures. It is used mainly in high end computer graphics, where it's high cost could justified. It used a format that came to be known as D1.
Shortly after that, Ampex and Sony jointly developed D2, a digital composite VTR. It quickly became the rage, and many machines were sold. Unfortunately, the format died an abrupt and early death, along with Panasonic's D3 digital composite format(Developed by NHK), when the expectation of Advanced Television being component-based pretty much ended any interest in composite anything.
As soon as it became apparent that component was the way to go, and digital compression became an unavoidable fact of life, three new digital formats emerged. (Digital video compression is considered to be a very bad thing by many video people because it involves intentionally throwing out picture details to save signal bandwidth. This could be the subject of another whole tutorial, but there are better versions of that on the 'net than I could ever write!)
The first of these was Ampex's DCT format. It has not gotten real popular, yet it is in use in a lot of well-known facilities. Panasonic introduced a non-compressed component format, called D5. It does not use any video compression at all. (DCT and Digital Betacam use 2:1 compression which in reality causes virtually no picture degradation.) Despite being the only machine of this class that is truly D1 quality, it has only slowly become popular. A compressed High Definition version of this format, called D5-HD has also become quite popular.
Sony introduced Digital Betacam
Sony introduced Digital Betacam (D8), which took off overnight. It uses an advanced version of the Beta-SP cassette, and a few models will actually play back analog Beta-SP tapes as well as digital! This format is Sony's most successful videotape format ever, and has (1999) become the next de facto high-end videotape standard.
One very high performance digital VTR built early on was the Sony HDD-1000. It was designed for recording High Definition TV pictures consisting of three channels of 30 MHz wide video. Along with this went eight channels of digital audio. The tape transport and scanner were modified 1" type C parts. The tape used was a 1" metal particle tape. The machine could record an amazing 1.25 gigabits of data per second! It only cost $360,000 in 1994.
Philips has recently introduced a new videotape format, which has been assigned the SMPTE standard D6. It is a cassette-based format using the D2 type cassette. It is capable of more performance than the HDD-1000 and can be adapted easily to ant TV standard, current or proposed! Like D5, it has been slow to catch on, but shows signs of becoming a viable HD format.
Sony has introduced an extension of their Digital Betacam format, called HDCAM. This format is a compromise digital VTR that uses both bandwidth limiting and digital compression to make a practical digital HDTV VTR. It is also the only HD format available in a camcorder.
The real excitement in digital videotape right now lies in a group of low-end formats, all of which are vying for a spot in this market as the de-facto standard. Two of these are based on 1/2" tape: Betacam SX and D9 (Digital S). Betacam SX uses the Beta cassette shell, and records compressed component video using MPEG2 Studio Profile@Main Level compression. It is intended for field acquisition.
D9 is the VHS version of Betacam SX, and uses the VHS cassette shell. It uses a mild 3.3:1, DV-based compression, and is intended for general use. Of these two, D9 has won hands down. Users have been reporting unbelivable video head life, sometimes in excess of 10,000 hours! a 100 Megabit/sec. version of D9 is in the works.
Three digital formats using 1/4"
Three digital formats using 1/4" tape have recently been introduced, one of them intended for consumer use. This format, which used to be called DVC is now simply called DV. It uses evaporated metal tape to record up to two hours on an approx. 8 mm-sized tape. A mild 5:1 intraframe video compression scheme is utilized, and picture quality is extremely good; certainly better than anything the consumer has heretofore had! A few camcorders using the DV format are currently available. Decks will be available as soon as the copyright people can rest assured that no one can pirate digital copies of movies with the machine!
The DV format is so good that Panasonic created a professional version called DVC pro (D7). Although it uses the same basic compression and recording scheme, it has a number of features to facilitate editing, etc. Not to be outdone, Sony has introduced the equally useful (and incompatible) format called DVCAM. (Again, DV with extra features to facilitate professional use.) There has been a war to see which of these formats will catch on and take the market, and Panasonic appears to be the winner. They have introduced higher bit rate versions of DVCPRO, called DVCPRO50 and DVCPRO100. DVCPRO50 is similar in performance to D9. DVCPRO100 is intended as a low-end HDTV format. It is just (1999) reaching the marketplace. DVCAM, though a good product, has not sold nearly as well.
Things have not stood still in the consumer world. DV is doing well in the marketplace. However, a new format, based on 8 MM has arisen to challenge it. It is called digital-8, not to be confused with SMPTE D8 (Tentatively Digital Betacam.) It uses ordinary Hi-8 videocassettes, although standard 8 cassettes will work, too (With reduced performance). This format, available from several Japanese vendors, appears to be a potential winner. (This format is so new that I have little info on it on the 'VTR formats' page. Apparently, the compression format used is intraframe, which will allow easy editing.)
Another format, intended as a home format, has been introduced. It is called D-VHS, and is intended for recording direct digital bitstreams from satellite and DTV broadcasts. It has several quality levels, one of which allows up to 49 hours (!) to be recorded on one cassette. Although it originally looked like this format could only be used to record digital video from satellites, it now appears that this format will come to be usable for all day-to-day digital video recording needs. Note that these machines have an elaborate copy-limiting algorithm built in that will allow everything from no copies to unlimited copies. Despite this, copyright issues forced these machines off the shelves in early 2000. It has returned to the shelves as of late 2003, but has not been really popular.