Index


Video Signal Storage

    Video tape

    A video cassette recorder (VCR) encodes standard video NTSC (or PAL or SECAM) signals on magnetic tape. There are many systems for that.Modern VCRs - both consumer and professional - are based on what is knownas helical scan recording. The main technological challenge that confrontedthe designers of early video recording machines was achieving the necessarybandwidth - several MHz - to faithfully capture the high frequency videosignal. In analogue video systems (like VHS, S-VHS, 8mm etc) signals are recorded in analog and no major alterations are made to the video. Most video systems use rotating video head system where write/read heads mounted on the video head assembly. Generally there are two write/read heads mounted 180 degrees apart (the can be more of those on some systems). The video tape is wound on the head drum at slightly more than 180 degrees. This allows for a slight overlap in information between the heads, which is necessary to be able to give out continuous video signal. The tape is wrapped on the drum at an angle, which causes that rotating video head generates tracks that are at a steep angle to the tape (5 - 6 degrees depending on the tape format). The tracks are scanned alternately by those two video heads. During the playback of the tape, the video heads are timed to swich from one to another in the redundant region in the "blacker than black" area below the bottom of the TV. All practical analogue video systems use this principle. Video recording bandwidth is determined by the modulation method, tape particle size, record/reproduce head design, internal electronic circuitry, and a variety of other factors. The higher the bandwidth the better. Higher bandwidth means higher resolution that means sharper pictures.Maximum luma bandwidth is reported by the manufacturers at the point at which the signal falls to 63 percent of its original value (-4.0 dB). The high frequency content of the image, such as very small objects with sharply-defined outlines (leaves of trees in backgrounds, blades of grass, and the like) is attenuated in the recording process. The visible effect of attenuation is a combination of lower brightness levels and blurring of tiny objects. Maximum chroma bandwidth is reported at the 63 percent or 71 percent (-3.0 dB) loss point. Digital video systems (DV, D8, DVCpro etc.) are entire another story. Those convert the video signal to a digital format. This digital video signal is then compressed. Those compressed bits are then recorded to the tape using suitable modulation and similar rotating video heads as used in analogue systems. During the recording process necessary error correction information is added to the tape. In the playback process, the bits are read from tape, bit error that can be corrected are corrected and the results are played back (image information decompressed and displayed out). Currently, all digital formats must be converted to analog NTSC or PAL formats for transmission, display on conventional TV monitors, and/or recording to analog tape. VCR systems are generally designed for one TV system. European VCRs support generally PAL format only (they do notsupport NTSC or PAL 60).VCRs sold in USA generally support only NTSC video format.Generally copy from NTSC source to an European VCR, it is necessary to convert the video output to real PAL (50Hz, 4.43 MHz colour signal). Conversion is also needed if you want to record PAL signal to NTSC VCR.There are some expensive multi-standard VCRs around nowadays.Some European VCRs nowadays have also extra feature to playback also NTSC tapes.

      Analogue video tape formats

      Analog refers to changing the original signal acquired (in a camera) into something that represents the signa - in this case, into a wave form transfered through video cable stored to a video tape.The process of storing this signal is not ideal, so some details of the picture are always lost when storing it to a video tape.Analog signals corrupt as you transmit the signal from the camera to the recorder and on to another recorder (editing).

      The most common video system for home use is VHS. When recording video signal to VHS tape two major changes are made to the NTSC signal: The Y signal (intensity and sync) is FM modulated and centered at approximately 3.5 MHz and the C signal (color) is moved downward in frequency and centered at approximately 600 kHz. In the recording process the bandwidth of Y anc C components is quite much limited (because of limitations of the bandwidth provided by those modulation methods). During the playback the conversions are done in the other way around. When recording PAL signals the principle is same, only the frequencies are somewhat different. The VSH format is know about the fact that the picture quality is quite limited, and the picture quality degrades quite quicly if you make tape to tape copied of VHS tapes.

      Conventional VHS machines have a pretty low quality monoaural sound track that is roughly equivalent to analog audio cassette. (This is known as the "linear track", a separate head track on the edge of the tape). Some professional VHS equipment has stereo linear tracks where the narrow strip at th edge of the tape is divided between two tracks (for left and right). VHS Hi-Fi is an improved stereo audio recording/playback system found on some camcorders and VCRs. VHS "Hi-Fi" features stereo tracks of moderately high quality recorded as an FM subcarrier along with the video. VHS "Hi-Fi" gives very good sound quality, but is subject to head switching problems (interchange between machines) audible as a slight buzzing sound. But recording and replaying on the same machine is usually reliable.

      There are several variations of VHS systems in use. VHS-C (VHS-Compact) is a miniature version of the VHS* tape format utilizing smaller cassettes that may also be played on standard VHS machines by using an adapter cartridge. S-VHS (Super VHS) is an improved version of the VHS tape format capable of recording better picture resolution. A higher-density tape is required which provides a wider luminance bandwidth, resulting in sharper picture quality (more than 400 horizontal lines vs. 240 for standard VHS) and improved signal-to-noise ratio. S-VHS-C (Super VHS-C) is an improved version of the VHS-C. It used VHS-C size cassette but stores the video signal there in S-video format. SVHS ET is a feature in S-VHS recorder that allows the machine to record in SVHS mode on a normal (good quality) VHS tape. When it does this it does 2 things, it bypasses the SVHS sensor and it preamplifies the higher range of the frequencies beingrecorded to the tape in an attempt to offset the higher degree of loss that will happen in that frequency range on the less broadbanded VHS tapes.

      8 mm is a compact videocassette record/playback tape format which uses eight millimeter wide magnetic tape. A worldwide standard established in 1983 allowing high quality video and audio recording. Flexibility, lightweight cameras and reduced tape storage requirements are among the format's advantages.Hi8 is an improved version of the 8mm tape format capable of recording better picture resolution (definition). A higher-density tape is required which provides a wider luminance bandwidth, resulting in sharper picture quality (over 400 horizontal lines vs. 240 for standard 8mm) and improved signal-to-noise ratio. Camcorders using this format are very small, light and provide a picture quality similar to S-VHS. Both S-VHS and Hi8 video are recorded in a slightly different fashion than their lower resolution counterpart (VHS and 8mm). The luminance portion of the video signal is allocated a substantially wider bandwidth on the frequency spectrum. An S-VHS and Hi-8 video signal is approx. 400 lines resolution, while a VHS or 8mm video signal is approx. 220 lines of resolution.

      Betacam is a high quality professional video format based apon the component video standard. Betacam is a portable, professional camera/recorder format developed by Sony. Betacam format is a defacto broadcast video format world-wide. Betacam format records all three signal components (Y,U,V) independently so that there is minimal signal loss during the record/playback process. It is able to do this by using a process known as Compressed Time Division Multiplex.The signal carrying the colour information, U and V, is time compressed and recorded on to one video track while the luminance, or Y, signal is recorded onto a second track. The use of two separate tracks eliminates the cross colour and cross luminance effects inherent in composite recording. Both tracks are recorded using high frequency FM (frequency modulated) carriers.Both oxide Betacam and Betacam SP produce image quality superior to S-VHS and Hi8 formats, primarily because of Betacam's separate recording tracks for luminance (Y) and chroma (Cr and Cb), rather than the color-under modulation method of S-VHS and Hi8. Betacam SP is a superior performance version of Betacam. Betacam SP uses metal particle tape and a wider bandwidth recording system(which gives better picture quality).The majority of broadcast electronic news gathering (ENG) operations currently use Betacam SP camcorders and VTRs. Virtually all broadcast stations require (or at least strongly prefer) Betacam SP source footage. Nowadays this demand for for Betacam SP footage has changed somewhat to prefer the new digital vidoe formats (DV, DVCAM etc..).

      MII is a portable, professional video component camera/recorder format, utilizing 1/2" metal particle videotape. MII is a professional videocassette format developed by Panasonic in 1986 as their answer & competitive product to Sony's Betacam SP format. It was technically similar to Betacam SP, using metal-formulated tape loaded in the cassette, and featuring component video recording. MII is sometimes incorrectly referred to as M2, the official name uses Roman numerals, and is pronounced "em two". MII was somewhat successful when it was first launched in the late 1980s, but MII not being nearly as successful as Betacam SP. MII is not widely used nowadays, and spare parts as well as tapes for the format are now hard to come by.

      U-matic is a video format designed in the late sixties/early seventies.The U-matic format was the fore-runner to all home video formats. The format was intended for professional use and so advanced features enabling full editing functionality were designed into the system from the start. U.matic uses a quite large 3/4 inch wide tape. There are three U-matic variants: Low, High - Band and SP. The original U-matic format is known as Lo-Band. The Hi-band system uses increased frequency carriers for improved picture quality and was the very first cassette based broadcast video format. SP, which stands for Superior Performance, is a further enhanced variation on the format which uses chrome tape for better video response and lower noise. Today, with the exception of a few African broadcasters, the SP variant is all but dead. The Low and Hi Band versions live on though. Hi Band is still used in studios as a companion to Betacam and Lo Band is firmly established amongst advertisemnet agencies and corporate establishments as the industry standard presentation format because of its reliability when compared to domestic alternatives. Low and Hi-band formats are not interchangeable.

      Betamax is a home video cassette format developed by Sony. Betamax was once popular, but long time ago VHS has taken over the home VCR world. Betamax is practically not used nowadays.The V2000 system was developed Philips to superceed their earlier video systems. V2000 did not ever come very popular.

      Comparision of some common analogue video formats:

      Format        Sync. tip    Peak white    Total FM   Luminance    Implied    S/N ratio
      frequency frequency deviation resolution Bandwidth (Luminance)
      (MHz) (MHz) (MHz) (TV-Lines) (MHz)
      VHS 3.4 4.4 1.0 240 3.0
      SVHS 5.4 7.0 1.6 400 5.0 46 dB (pro)
      (Beta 1) 3.5 4.8 1.3 250 3.1
      SuperBeta 4.4 5.6 1.2 285 3.5
      ED Beta 6.8 9.3 2.5 500 6.3
      Betacam SP 2.0 330 4.1 46..50 dB
      Betamax 260 3.2 40 dB
      U-Matic 250 3.1 46 dB
      U-Matic SP 330 4.1 46 dB
      DV Formats 500 6.3
      Hi8 400 5.0 45 dB (pro)
      For comparision purposes:
      Typical NTSC Broadcast                                330          4.1    DVD Video                                             500          6.3

      Video recording bandwidth is determined by the modulation method, tape particle size, record/reproduce head design, internal electronic circuitry, and a variety of other factors. Maximum luma bandwidth is reported by the manufacturers at the point at which the signal falls to 63 percent of its original value (-4.0 dB). Maximum chroma bandwidth is usually reported at the 63 percent or 71 percent (-3.0 dB) loss point.

      VCRs are typically devices that work with one TV system only. For this reason there are versions of the commonly used video systems for different TV standards (uses same tape but store different signal to tape in slightly different way). There are also multisystem VCRs that can handle more than one TV standard. Multisystem VCRs can be divided into two groups: those that convert the recorded standard to a selected standard (but they may not support all the standards as a conversion output option), and those that do not do any conversion at all (you must have a TV of the standard desired). It is certainly possible some units won't really include every standard and could have limits what they can do with different formats. For example at consumer video marker you can find VHS VCRs for PAL standard that can play back both PAL and NTSC tapes, but can only record to PAL standard.

      Digital video tape formats

      The term digital video means here a video that is shot by a digital camcorder.The quality and glamour of digital video is that it can begin and remain digital from camcorder to computer.Standardized digital interface is the lifeline of the digital video enthusiast. It allows th euser to transmit the video material in digital format form the camera to the computer (and usually also back) without loss of picture quality. No matter how many copies (generations) are created, the video signal remains at good quality (unless the video signal is processed on the way or there are lots of transmission errors). Digital video systems convert the video signal (from video sensor in camera or form video input analogue signal) to a digital format for processing and storage purposes. This conversion is made using a process called sampling, which takes samplesof the incomign video signal and convert them to a series of numbers.DV-NTSC uses 4:1:1 sampling in which the chroma is sampled once for every four horizontal luminance samples. DV-PAL uses 4:2:0 sampling, which uses the average value of the chroma signal between successive horizontal samples and scan lines. After sampling digital video signal is then compressed. Those compressed bits are then recorded to the tape using suitable modulation and similar rotating video heads as used in analogue systems. During the recording process necessary error correction information is added to the tape. In the playback process, the bits are read from tape, bit error that can be corrected are corrected and the results are played back (image information decompressed and displayed out). Currently, all digital formats must be converted to analog NTSC or PAL formats for transmission, display on conventional TV monitors, and/or recording to analog tape. At 1997 Mini DV is introduced as a new, higher definition, digital recording format. Perfect copies can be made from them without loosing any quality. DV is nowadays a popular digital video camera format used for consumer and semi-professional use.MiniDV is the "low-cost" digital video (DV) format targeted for comsumer use.The resolution quality of MiniDV and Betacam SP are perceptively similar (=very good). MiniDV has some limitations. The DV and MiniDV formats use IEEE 1394 interface (also known with names like DV-link and i.Link) for connecting the camcoder to a computer to transfer the video in digital format.Digital8 is a variation of MiniDV (introduced at 1999). It is technically very similar to MiniDV.The difference is that Digital8 uses different tape than other DV systems (Digital8 uses 8 mm tape).Digital S, DVCPRO, and DVCAM formats are the top three commercial digital formats offered by JVC, Panasonic, and Sony, respectively. Even though they are all digital, they are not compatible. The comparative value of one over the other is a matter of personal preference. The three commercial digital formats share a digital output standard called Serial Digital Interface (SDI). This format is the way digital-format recorders transmit their digital video to other digital equipment, such as other digital recorders or computers.DVCAM and DVCPRO are swiftly overtaking Betacam SP and will soon be the most popular formats for professionals. Newest digital video format is high-definition HDV format developed by Canon, JVC, Sharp and Sony. HDV stores HDTV quality picture (16:9 format 1920x1080 pixels) to DV casette using MPEG2 video compression. The videos from HDV system is transferred to computer through DV-link (i.Link / IEEE 1394).

      D-Theater / D-HDS

      . The latest contender in home theater gadgets market is digital tape, D-VHS and the new D-Theater format stored to it. JVC, on the hardware end teamed up with four major film studios, Twentieth Century Fox, Universal, DreamWorks, and Artisan to support this new format. Basically, this format is aimed at the small but growing owners of high definition televisions (HDTV). The studios have opted to release their films on an optional system within the D-VHS format, called D-Theater. Created by JVC specifically for copyrighted, high value prerecorded content, D-Theater provides a state-of-the-art level of security demanded by content producers in the digital era. D-Theater is a new high definition D-VHS platform. It is totally digital technology. D-Theater technology will be applicable to prerecorded HD content.The video formats supported are listed as 480i, 480p, 720p, 1080i, and 1080p. Initially, the video mode will be 1080i. There is the ability to play Dolby 5.1 sound and for multiple audio tracks to be present (possiblity for DTS sound may be added later).D-Theater high definition software will be recorded in the D-VHS HS (High Speed data rate) mode. (The HS mode is the optional mode in the D-VHS format that will allow HD content recording.) The storage capacity is around 44 Gig which should yield around 4 hours of high definition material. The bandwidth is 28 Mbps. An advanced proprietary encryption system is employed to achieve content protection. Tapes with genuine data can be created only on duplication equipment licensed and approved by JVC. Region code will be imposed on this format. D-Theater is not not downward compatible with previous D-VHS hardware. D-Theater video software, identified by a prominent D-Theater logo on the packaging, will be playable only on D-VHS video recorders bearing the same D-Theater logo. The material is designed to be played back to HDTV display, but with the standard S-Video output you can view a downconverted 480i/p on a non-HDTV set. D-Theater machines will also play regular D-VHS and VHS tapes. D-VHS is not meant to compete with DVD or VHS, both of which are designed for the mass market. Instead, the D-VHS format and its players offer owners of high-definition TV sets the option of recording and watching high-quality video. It is expected that this format is going to coexist with VHS and DVD by serving a niche market of videophiles

      VCR copy protection

      VCR copy protection systems are designed to prevent consumers to copy video material to their own VCR. The most commonly used and best known video protection system for this is called Macrovision. Macrovision is an analogue copy protection of Videotapes, DVD movies and pay-per-view television (Analogue signal). Its purpose is to make it harder to record such signals with a VCR. Generally the protection must be disabled or removed, before recording by a VCR is possible. Macrovision is the most commonly used antitaping process for VHS video tapes and digital video systems.Around 95% if VCRs on the market do not record Macrovision protected signal with any usable quality. If you try to copy a Macrovision-protected tape, the copy becomes crappy and not worth seeing, the picture changes brightness with time and the color is distorted. Not all TV's work very well with this form of protection e.g. the top of picture is distorted and it might look like the tape is damaged. Macrovision is based on using a hyper-brightsync pulse (to confuse the AGC of a VCR) and also does things to the chromato further confuse such. Macrovision works due to the differences in theway VCRs and TVs operate. The automatic gain control circuits within a TV are designed to respond slowly to change. Those for a VCR are designed to respond quickly to change. The Macrovision technique attempts to take advantage of this by modifying the video signal so that a TV will still display it but the VCR will not record a viewable picture. CGMS is Copy Guard Management system for NTSC systems. A method of preventing copies or controlling the number of sequential copies allowed. CGMS is transmitted on line 20 for odd fields and line 283 for even fields for NTSC. For digital formats it is added to the digital signal conforming to IEEE 1394.

    Disc based video storage

      DVD

      DVD information has been moved from here to a separate DVD page in this site.

      Laserdisc

      LaserDisc is a laser read optical disc system used for the reproduction of video and audio signals. The system reproduces a full bandwidth analogue video signal with around 7MHz response, along with dual FM coded analogue audio signals.

      VideoCD

      VCD stands for 'Video Compact Disc' and basically it is a CD that contains moving pictures and sound. VCDs look exactly like a CD or CD-ROM except that it stores video/audio clips using the compressed and standardized MPEG 1.A VCD has the capacity to hold up to 74 minutes on of full-motion video along with quality stereo sound (this is 650 MB of data). VCD can store up to 80 minutes of full-motion video along with quality stereo sound to a 80 minute CD (700 MB CD). In addition to those a VCD can also inclue menus, chapters, photo albums and slide shows with background audio. VCD resolution is 352x288 for PAL and 352x240 for NTSC. VCDs use a compression standard called MPEG-1 to store the video and audio. The picture quality of VCR is generally considered to be about the same as VHS tape, but not always as good as VHS. Video CD (VCD) is used as a low-cost alternative to DVDs in Asia. A VCD can be played on almost all standalone DVD Players and on practically all computers with a DVD-ROM or CD-ROM drive with the help of a software based decoder / player. . However not all DVD players will play VCD's - this is not the fault of the VCD but the compatibility of the DVD player.

      • Videohelp.com - This site will help you to make your own VideoCDs, SVCDs or DVDs that can be played on your standalone DVD Player from video sources like DVD, Video, TV, Cam or downloaded movie clips like DivX, MOV, RM, WMV and ASF. We also have an extensive list of standalone DVD Players with compatibility information such as CD-R(W), DVD-R(W), VCD, SVCD, MP3 and more.    Rate this link

      SuperVideoCD

      Super Video CD (aka SVCD, Super VCD or Chaoji VCD) is an enhancement to Video CD that was developed by a Chinese government-backed committee of manufacturers and researchers, partly to sidestep DVD technology royalties and partly to create pressure for lower DVD player and disc prices in China. The final SVCD spec, set by the China National Committee of Recording Standards, was announced in September 1998, winning out over C-Cube's China Video Disc (CVD) and HQ-VCD (from the developers of the original Video CD). SVCD can deliver 480x576 resolution for PAL material and 480x480 resolution for NTSC. SVCD can support variable bitrate (VBR) MPEG-2 video up to 2.6 Mbps (need 2x CD), and either 1 or 2 MPEG-2 Layer II stereo audio streams (for soundtracks in two different languages). It is also possible to use MPEG-2 Multi-Channel 5.1 surround audio encoding.SVCD has extensive support for subtitling and karaoke lyrics color highlighting. . An SVCD video stream can contain up to four independent subtitling channels for different languages. The subtitles are overlaid on the top of the video image in real time. Additionally, SVCD standard supports HTML style hyperlinks, still images (480x576 or 704x576 for PAL, 480x480 or 704x480 for NTSC), playlists/slideshows, multi-level hierarchical menus and chapters (indexing). SVCD is currently in the process of IEC standardisation (see IEC document title "IEC 62107"). This means that SVCD is about to become an internationally recognized CD standard (just like Video CD 2.0 or CD-DA already are), although it is uncertain whether it will actually find commercial applications outside China and nearby countries. SVCD titles are currently commercially available at least in mainland China, Hong Kong, Taiwan, Malaysia, Thailand, Singapore and India.Lately, relatively cheap stand-alone DVD / SVCD / VCD / MP3 players have been appearing all over the western world.


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