Audio Video Formats
Technical overview for Audio Video Formats
The three formats (Video8, Hi8 and Digital8) are physically very similar, featuring both the same tape-width and near-identical cassette-shells measuring 95 x 62.5 x 15 mm. This gives a measure of backward-compatibility in some cases. One difference between them is in the quality of the tape itself, but the main differences lie in the encoding of the video when it is recorded onto the tape.
Video8 was the earliest of the three formats, and is entirely analog. The 8 mm tape width was chosen as smaller successor to the 12mm Betamax format, using similar technology (including U-shaped tape loading), but in a smaller form factor and in response to the small form factor VHS-C compact camcorders introduced by the competition. It was followed by a version with improved resolution, Hi8. Although this was still analog, some professional Hi8 equipment could store additional digital-stereo PCM sound on a special reserved track.
Digital8 is the most recent 8 mm video format. It retains the same physical cassette shell as its predecessors, and can even record onto Video 8 (not recommended) or Hi8 cassettes. However, the format in which video is encoded and stored on the tape itself is the entirely digital DV format (and thus very different from the analog Video8 and Hi8). Some Digital8 camcorders support Video8 and Hi8 with analog sound (for playback only), but this is not required by the Digital8 specification.
In all three cases, a length of 8 mm-wide magnetic tape is wound between two spools and held within a hard-shelled cassette. These cassettes share similar size and appearance with the audio cassette, but their mechanical operation is far closer to that of VHS or Betamax videocassettes. Standard recording time is up to 180 minutes for PAL and 120 minutes for NTSC. (The cassette holds the same length tape – tape-consumption is different between PAL and NTSC recorders.)
Like most other videocassette systems, Video8 uses a helical-scan head-drum to read/write video to the magnetic tape. The drum rotates at high speed (one or two rotations per picture frame – about 1800 or 3600 rpm for NTSC, and 1500 or 3000 rpm for PAL) while the tape is pulled along the drum's path. Because the tape and drum are oriented at a slight angular offset, the recording tracks are laid down as parallel diagonal stripes on the tape.
Audio Video Formats - Generations
Video8
Video8 was launched into a market dominated by the VHS-C and Betamax formats.
In 1983 Sony Betamax had released the first camcorder called Betamovie. In response JVC released the compact VHS-C format which enabled the first handheld (rather than shoulder-mounted) camcorders. Sony's answer to these small cameras came in 1985 when they used Betamax-style U-load technology, but reduced the tape width from 12 millimeter to 8 millimeter, and the Video8 format was born.
In terms of video quality, Video8, VHS/VHS-C, and Beta-II offered similar performance in their "standard play" modes; all were rated at approximately 240 horizontal lines (depending on speed, quality of tape, and other factors). In terms of audio, Video8 generally outperformed its older rivals. Standard VHS and Beta audio was recorded along a narrow linear track at the edge of the tape, where it was vulnerable to damage. Coupled with the slow horizontal tape speed, the sound was comparable with that of a low-quality audio cassette. By contrast, all Video8 machines used "audio frequency modulation" (AFM) to record sound along the same helical tape-path as that of the video signal. This meant that Video8's standard audio was of a far higher quality than that of its rivals, although linear audio did have the advantage that (unlike either AFM system), it could be re-recorded without disturbing the underlying video. (Betamax and VHS Hi-Fi rarely appeared on camcorders, except on the high-end models.) Video8 later included true stereo, but the limitations of camcorder microphones at the time meant that there was little practical difference between the two AFM systems for camcorder usage. In general, Video8 comfortably outperformed non-HiFi VHS/Beta.
Video8 had one major advantage over the full-sized competition. Thanks to their compact-form factor, Video8 camcorders were small enough to hold in the palm of the user's hand. Such a feat was impossible with Betamax and VHS camcorders, which operated best on sturdy tripods or strong shoulders. Video8 also had an advantage in terms of time, because although VHS-C offered the same "palmcorder" size as Video8, the VHS-C tapes only held 40 minutes of time (SP). Thus Video8's 120-minute capacity served well for most users. (Both machines included longer playing modes at 120 and 240 minutes respectively, but at the cost of reduced quality images of only 220 lines resolution.) Longer sessions generally required additional infrastructure (AC power or more batteries), and hence longer recording-times offered little advantage in a true travelling environment.
Video8/Hi8's main drawback was that tapes made with Video8 camcorders could not be played directly on VHS hardware. Although it was possible to transfer tapes (using the VCR to re-record the source video as it was played back by the camcorder), this inevitably led to degradation of the analog signal.
Ultimately, Video8's main rival in the camcorder market turned out to be VHS-C, with neither dominating the market completely. However, both formats (along with their improved descendants, Hi8 and SVHS-C) were nevertheless very successful. Collectively, they dominated the camcorder market for almost two decades before they were eventually crowded out by digital formats such as MiniDV and DVD recordable.
Hi8
To counterthe introduction of the Super-VHS format, Sony introduced Video Hi8 (short for high-band Video8.) Like SVHS, Hi8 used improved recorder electronics and media-formulation to increase picture detail. In both systems, a higher-grade videotape and recording-heads allowed the placement of the luminance-carrier at a higher frequency, thereby increasing luminance bandwidth. Both Hi8 and SVHS were officially rated at a luminance resolution of 420 horizontal TV/lines (560x480 in today's digital terms), a vast improvement from their respective base-formats of 240 lines and roughly equal to laserdisc quality. Chroma resolution for both remained unchanged at approximately 30 lines horizontal. All Hi8 equipment supported recording and playback of both Hi8 and legacy Video8 recordings. Video8 equipment cannot play Hi8 recordings.
Both S-VHS and Hi8 retained the audio recording systems of their base formats; VHS HiFi Stereo outperformed Video8/Hi8 AFM, but remained restricted to high-end machines.
In the late 1980s, digital (PCM) audio was introduced into some higher grade models of Hi8 (and SVHS) recorders. Hi8 PCM audio operated at a sampling rate of 32 kHz with 12-bit samples -- far short of CD-audio or SVHS PCM quality. PCM-capable Hi8 and SVHS recorders could simultaneously record PCM stereo in addition to the legacy (analog AFM) stereo audiotracks.
The final upgrade to the Video8 format came in 1998, when Sony introduced XR capability (extended resolution). Video8-XR and Hi8-XR offered a modest 10% improvement in luminance detail, while retaining full backward compatibility with older non-XR equipment. XR recordings were fully playable on older non-XR equipment, though without the benefits of XR.
Audio Video Formats - Digital8
Hitachi Digital8 Camcorder
Introduced in 1999, Digital8 is digital video recorded on Hi8 media using the industry standard DV codec. In engineering terms, Digital8 and miniDV are indistinguishable at the logical format level. Digital8 uses the same cassettes as Video8, but otherwise bears no resemblance to the Video8 analog video system. Some Digital8 equipment can play (not record) Hi8/Video8 recordings, but this is not a standard feature of Digital8 technology. To store the digitally-encoded audio/video on a standard NTSC Video8 cassette, the tape must be run at double the Hi8 speed. Thus a 120 minute NTSC Hi8 tape yields 60 minutes of Digital8 video. Most Digital8 units offer an 'LP' mode, which increases recording time on a NTSC T-120 tape to 120/2 * 1.5 == 90 minutes.
For PAL, the Digital8 recorder runs one-and-a-half times faster, thus a 120-minute PAL Hi8 tape yields 90 minutes of Digital8 video.PAL LP mode returns the tape speed to the Hi8 SP speed, so a Hi8 120 minute tape yields 120 minutes of Digital8 video.
Sony has licensed Digital8 technology to at least 1 other firm (Hitachi) who marketed a few models for a while, but presently, only Sony sells Digital8 consumer equipment. Digital8's main rival is the consumer miniDV format, which uses narrower tape and a correspondingly smaller cassette shell. Since both technologies share the same logical audio/video format, Digital8 can theoretically equal miniDV in A/V performance. But as of 2005, Digital8 has been relegated to the entry-level camcorder market, where price and not performance is the driving factor. Meanwhile, miniDV is the de facto standard of the digital camcorder market, with DVD recordable camcorders also increasing in popularity due to the ability to take the media from the camcorder straight to a standard DVD player.
Tape and recording protection
As with many other video cassette formats, 8 mm videocassettes have a tape-protecting mechanism built into the shell. Unlike the ones on VHS and VHS-C shells, which consist of only a singular piece of plastic that protects the part of the tape that is read by the player/recorder, Hi-8's tape protection mechanism consists of two pieces of plastic at the top of the shell that come together and form a casing that protects both sides of the tape, and a latch that prevents this casing from opening and exposing the tape. The playback/recording unit can depress this latch to open the casing and gain access to the tape.
To prevent the recording on the tape from being erased, there is a small "write-protect" tab that can be moved to one of two positions, labeled "REC" and "SAVE", respectively. The tape can only be recorded on (or recorded over) when this tab is in the "REC" position. This is an improved version of the VHS write-protect tab, which prevents erasure after it has been (permanently) broken off.
Video8 outside the camcorder market
Efforts were made to expand Video8 from the camcorder market into mainstream home video. But as a replacement for full-size VCRs, Video8 failed. It lacked the long (5+ hour) recording time of both VHS and Betamax, offered no clear audio/video improvement, and cost more than equivalent full-size VCRs. Quite simply, there was no compelling reason to switch to Video8 for the home VCR application.
Initially, many movies were prerecorded in 8 mm format for home and rental use. The rental market for Video8 never materialized. Sony maintained a line of Video8 home VCRs well into the 1990s, but unlike VHS, 8 mm VCRs with timers were very expensive.
Sony also produced a line of video 8 mm Walkman-branded players and recorders with and without a flip up screen meant for video playback and limited recording. These have been adapted for digital 8 mm as well as miniDV formats even as portable DVD players have become popular in this application. Such players saw use in professional applications, particularly with airlines who, during the 1980s, adopted 8 mm as the format for in-flight movies. As of 2008, they remain in use on many airliners.
Among home and amateur videographers Video8/Hi8 was popular enough for Sony to make equipment for video-editing and production. The format also saw some use in the professional ENG/EFP field.
The future of the 8 mm video formats
As of early 2007, the analog 8 mm formats are nearing the end of the road. Standard Video8 is already extinct in the new camcorder market. Hi8 (along with VHS-C) is still used for some entry-level camcorders aimed at consumers, but elsewhere has been almost entirely superseded by digital formats, such as its successor Digital8, miniDV, and miniDVD. However, both standard Video8 and Hi8 videocassettes remain widely and inexpensively available.
Some have questioned the future of Digital8, citing the fact that (as of early 2007) only Sony supported the format in the face of competition from MiniDV, and only in their entry-level camcorders. As of early September 2007, Sony's last Digital8 camcorder, the DCR-TRV280, has been removed from their consumer lineup. (As of October 2007, the camera is still listed under their "business-to-business" section of their website.) Only two Digital8 devices now remain, both Digital8 video Walkmans. Sony has announced no plans for future models; it seems that we've probably seen the last of Digital8 camcorders, aside from remaining dealer stock and the used market, such as eBay.
Miscellaneous technical issues
Dropouts
In Video8 and its successors, the smaller head drum and tape left recorders more susceptible to the effects of 'tape dropout', where magnetic-particles are eroded from the tape surface. As the audio/video signal is held in a smaller area on a Video8 tape, a single dropout has a more damaging effect. Hence, dropout compensation in Video8 systems tend to be more advanced to mitigate the format's vulnerability to dropouts. In this respect, VHS and Betamax's larger head drums prove advantageous.
Lifespan of 8 mm Tapes
8 mm tapes should be stored vertically out of direct sunlight, in a dry, cool dust-free environment. As with any media, they will eventually deteriorate and lose their recorded contents over time, resulting in a build up of image noise and dropouts. Tapes older than 15 years may start to show signs of degradation. Amongst other problems, they can become sticky and jam playback units or become brittle and snap. Such problems will normally require professional attention.
However, the 8 mm format is no more prone to this than any other format. In fact, the metal particle technology used with the Video8 formats is more durable than the metal evaporated type used with MiniDV. Hi8 tapes can be either of Metal Particle (MP) or Metal Evaporated (ME) formulation.
Because 8 mm tapes use a metal formulation, they are harder to erase than the oxide tapes used with VHS, SVHS and Betamax tapes. As such, carefully stored, they are less susceptible to magnetic fields than the older formats.
Transferring 8 mm footage to a computer for editing
Because Video8 and Hi8 are analog video formats, transferring either to computer requires digitization. One method is to feed the video signal to an analog capture card connected to the computer itself.
Another option involves the use of a pass-through adapter which outputs a digitized video signal in the industry standard DV format. Many consumer-level miniDV and Digital8 camcorders have this facility built-in. The DV signal can then be fed into a computer equipped with a firewire port.
A third route is to find a Digital8 camcorder which supports legacy playback of Video8 and Hi8, and which will output a digitized DV signal directly via its firewire port. This will usually yield an improved image quality compared to the previously mentioned methods, and can offer the advantage of direct computer control over the tape transport, which is difficult (may require extra hardware) or impossible for the bridge method mentioned above.
Once on a computer, footage can be edited, processed and transferred to DVD, the Internet, or back to tape.
-Wikipedia