Video Recording

A video recording device allows moving pictures to be stored on a suitable recording medium, such as a video tape, video cassette or hard disk. Unlike traditional film, where the images are kept in optical form, a video recording retains the information in a specified video format. Although ‘video’ is less durable than film, it’s easier to handle and is convenient for electronic editing.

  A Short History

Up until the mid-fifties all television programmes were broadcast ‘live’ or were taken from cinema film. In the USA, investigations into the use of magnetic tape for video recording were made by Bing Crosby Laboratories and RCA. This technology was based on a fixed-head design, similar to an audio tape recorder but using much higher tape speeds to obtain the necessary frequency response. Unfortunately, a four-minute recording on an RCA machine consumed more than a mile of tape.

In 1956, Ampex produced a machine with four heads, positioned on a drum that rotated across the width of the tape. Unlike older recorders, this quad format used a 2-inch tape that moved at a reasonable speed. It was eventually used for colour and was a standard system for nearly 20 years.

Various other helical scan formats have since been used by professionals, whilst today, many broadcasters use digital video tape recorders. These first appeared in 1986, superseding all that came before. The established D-1 digital format was soon followed by other advanced systems.

Domestic Playback Systems

Early domestic video systems only permitted playback of existing material. One example, launched by CBS in 1968, was the film-based Electronic Video Recording System (EVR). Ten years later, Philips and MCA Laboratories introduced the LaserVision Videodisc, whose optical principles formed the basis for Compact Disc (CD). A 12 inch (305 mm) LaserVision disc accommodated over an hour of standard video material or 15 minutes of high-definition TV (HDTV), both with stereo sound. This format is still used in industry and education, although its days are numbered.

In 1981, RCA unveiled its curious Capacitance Electronic Disc (CED) system, which employed a grooved disk and a stylus: this was an unmitigated failure. The more successful Digital Versatile Disc (DVD) format, originally launched in 1995 as the Digital Video Disc, was developed from CD technology. Each DVD can hold an entire film, complete with surround sound and subtitles.

The Video Cassette Recorder (VCR)

It took two decades for video recording technology to move into the home environment. Even then, numerous different formats were introduced, many of which were unsuccessful.

In 1971, Sony released the U-matic format for domestic use. Although actually too expensive for the home, it was used by broadcasters for electronic news gathering (ENG). Unlike older reel-to-reel formats, the U-matic used a sealed tape cassette containing two horizontally-aligned spools.

In fact, this machine formed the basis of the modern video cassette recorder (VCR). Its cassette contained a 34-inch tape that was drawn out during playback and partially wrapped around the rotating drum in a ‘U’ shape, thus giving the format its rather curious name. This was known as a helical scan arrangement, the drum containing two or four heads and set at an angle across the tape.

By 1972, Philips had devised its own domestic N1500 VCR format, employing an unusual cassette that housed the spools one above the other. Unfortunately, this meant that both the cassette and machine were rather complicated, sometimes causing problems with reliability. The format went through several improvements, mainly to increase the playback time. Unfortunately, despite additional work by Grundig, the format was overtaken by other systems that used simpler cassettes.

Following the success of U-matic, Sony introduced Betamax in 1975, also using helical scanning but with smaller cassettes containing 12-inch tape. Although successful, it was soon overtaken by the similar Video Home System (VHS), first produced in 1976 by the Japan Victor Company (JVC), part of Matsushita Electric Industrial Corporation. RCA and Matsushita then introduced a long play (LP) variation of VHS, doubling its recording time and wiping Betamax off the commercial map. However, a derivative of the Beta format known as Betacam SP did become popular for ENG.

The VHS format also developed into a higher quality system known as Super-VHS (S-VHS). Despite the success of VHS, Sony still dominated the industry, introducing new analogue 8 mm formats, such as Video-8 and Hi-8. These were followed by a digital version known as Digital 8, as well as 4 mm digital systems such as MiniDV and DVCAM. These cassettes have seen the demise of the bulky VHS tapes used in older camcorders, although until recently some devices used a VHS-C cassette that could be fitted in an adaptor for playback in a normal VHS VCR.

However, the days of video tape are seriously numbered, especially with the introduction of Digital Versatile Disc (DVD) in the form of recordable DVD-R.

  Recording Systems

Most budding film producers use a conventional video camera linked to a video cassette recorder (VCR). Alternatively, you can use a modern camera with an integral recorder, commonly known as a camcorder. Unfortunately, several different types of video cassette are available.

Other points worth noting are:-

High Quality Cassette Systems

The following professional systems are in use:-

All these digital systems offer four channels of digital sound, with at least 16-bit sampling at 48 kHz. The following Digital Video (DV) formats are also available, using 720 pixels per line, offering up to 500 lines of horizontal resolution and employing a cassette containing evaporated metal tape:-

JVC manufacture a MiniDV recorder that provides an enhanced performance by recording MPEG-2 data onto the tape. In HiRes mode it operates at 25 frm/s with an image of 1280 × 659 pixels and an aspect ratio of 16:9. In progressive scanning mode at 50 frm/s (PS50) it can produce 941 × 485 pixels, with an aspect of 17:9, or 839 × 576 pixels, with a ratio of 4:3.
Some video players can play DV, DVCPRO, DVCAM and MiniDV cassettes.

All of the systems in this group use 4 mm tape in a cassette measuring 65 by 48 by 12 mm, making them more compact than Sony’s older analogue and digital 8 mm cassettes (see below).

DVCAM, often used by professionals, is Sony’s proprietary extension of the consumer MiniDV standard. The cassettes used for DVCAM contain an extra ‘chip’ that stores timecode information and can operate at a faster tape speed than MiniDV. This means that DVCAM cassettes contain more tape, although DVCAM recorders can also play MiniDV cassettes. The actual quality of recording provided by these two systems is very similar, although DVCAM recordings are more robust.

Although MiniDV is a consumer system, the picture quality is similar to DVCAM, is based on the standard 640 × 480 format and provides the usual horizontal resolution of up to 500 lines, although JVC uses a proprietary Super High Band processor to increase this to 530 lines.

All these systems record video in 8-bit digital component form, in 4:1:1 or 4:2:0 format and with 5:1 DV compression. An optional wide screen mode is available, accommodating an aspect ratio of 16:9. Two-channel stereo sound can be recorded in digital form using 12-bit or 16-bit PCM, although 12-bit resolution must be used for digital dubbing or recording 4-channel sound.

Consumer Cassette Systems

Several consumer formats are available, in addition to MiniDV (see above). The first group of systems, devised by Sony, are based on various types of 8 mm video cassette. Higher-quality models can usually play other types of 8 mm cassette. The following formats are available:-

The second group of systems are older analogue formats that employ a bulkier cassette:-

Recording to Hard Disk

Video material can also be recorded onto hard disk, either by using specialised hardware or by using a standard computer, preferably with a separate hard disk drive for the actual recording. For best results, you must also have adequate RAM and a suitable PAL or NTSC video monitor.

A video editing application lets you assemble video and sound material to create your own movie. This is very easy if you have a FireWire-equipped Mac OS computer, together with Apple’s iMovie application and a DV camcorder. Having got the material onto your computer, you can edit it and then send the results back to the camcorder, assuming the latter lets you record via FireWire.

The following table shows video data rates and the necessary transfer rates for a disk drive:-

QualityData (MB/s)Drive (MB/s)
DV*3.53.6
S-VHS22.25 to 3.5
VHS1.51.75 to 3
NTSC27•10

* 5:1 compression reduces 25 MB/s to 4.5 MB/s

Only with reduced resolution or screen size

Controlling Video Devices from a Computer

Some applications, such as Apple’s iMovie program can also control the transport of a camcorder via its FireWire connection, assuming your particular camcorder is supported by the application. In fact, any suitably-equipped computer can control other equipment during video editing, including a VCR or Laser Videodisc. Ideally, the mechanisms of all the devices you want to use should be controlled at the same time from the computer. This does of course require appropriate software and hardware.

During editing, the computer must know the exact point in a video recording where it should make an edit. Some Sony 8 mm camcorders have a Control-L socket that allows the tape to be marked to an accuracy of one second, which is then interpolated to ± 5 video frames.

More advanced equipment uses ViSCA (Video System Control Architecture) for ±1 frame accuracy. Such devices sometimes have a serial port. If not, you can use a V-box to connect the serial port on a suitable computer to a Control-L socket or ViSCA connector.

Editing

Recording images is one thing: getting them into a presentable form is something completely different. The process usually involves taking lengths of recordings that have been made at different times and putting them together in the required sequence, a process commonly known as editing.

Film Editing

In conventional film editing, the original film from a ‘shoot’ is considered very precious, mainly because of the time and money taken in its production. So, prior to editing, several copies of each original ‘take’ are made onto low-grade film to create what are known as ‘rushes’. Often, a smaller format is employed: for example, if the ‘takes’ are on 35 mm film then the ‘rushes’ are on 16 mm.

These films are then loaded onto a film viewing machine, which has two or three pairs of reels either side of a screen and a means of moving the reels separately or in step. Once viewed, the required lengths of film are cut and spliced together with transparent adhesive tape in a film editing block. The result goes onto a right-hand reel whilst unwanted material is spooled-off into a waste bin.

This technique ensures that any mistakes can be corrected by obtaining and editing further copies of the original ‘takes’. Only when everyone is entirely happy is it permissible to edit the original film. The editor then works with both the edited film and the original ‘takes’, using frame-by-frame comparison to ensure that the final result matches the edited version.

Video Tape Editing

Editing tape is similar to editing film, except that you don’t actually cut or join the tape. In fact, the original video tapes used for ‘takes’ aren’t ever touched by the editing process. First of all, each ‘take’, which is usually recorded on a professional format such as D-1, is copied using suitable machines to a sub-broadcasting format, such as U-matic. These cassettes are then taken to an offline editing suite, consisting of two or more sub-broadcasting video playback machines, a video mixer and a matching recording machine. The copies of the ‘takes’ are then played in turn and transferred via the video mixer to the recording machine: this process is known as dub-editing.

Nothing is done to the original ‘takes’ until offline editing is complete. Only then are the original tapes taken to an online editing suite, which has two or more professional video players, another video mixer and a matching recording machine. The process of dub-editing is now repeated, using the results of offline editing as a timing reference for the final editing.

Unlike film, video tape doesn’t incorporate sprocket holes or have any visible frames, so the provision of timing information is particularly important. To do this, timecode is recorded along with the video material on every tape, conveying time in hours, minutes, second and frames. So, when recording a ‘take’ the time of day is recorded onto the tape. Now, when the tape is used for offline editing, it’s possible to document the exact point where an edit is required on the original recording.

In fact, material originating from an offline editing suite usually conveys two sets of timecode: the time of day of the original recording and the time duration from the start of the compiled material. The work of online editing is normally assisted by employing an edit decision list (EDL). This usually includes a name of each continuous block of video within a pair of edits, the time of day for the start and end of each block, and the time duration values for the start and end of the blocks.

Armed with an EDL and appropriate equipment, it’s possible to compile the final tape without even seeing the offline recording. And, with suitable machines, the process can be semi-automatic.

Disk Editing

Working with a disk-based editor is similar to using video tape. However, you’ll be using the files that actually contain your ‘takes’, so, to be on the safe side, you should make copies of these before you start. In effect, your computer acts as an online editing suite, allowing you to quickly compile a final product. Unlike tape editing, however, the process is nearly always reversible.

EDL File Formats

An EDL file, as commonly used by video editing applications, is a simple ASCII document that describes the timing and types of edits used in a production. Typically, it deals with two levels of video over two or four tracks. It may also contain clip data, but not any real video or audio material.

Unfortunately, these files aren’t standardised. Some applications such as ProTools, as well as Avid-based systems, use Open Media Framework Interchange (OMFI) files, whilst products from Tascam and others often employ the Tascam Open Track List (OpenTL) format.

References

1997 Grolier Multimedia Encyclopedia, © 1997, Grolier Inc.

©Ray White 2004.