IT: Information
IT: Information

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IT: Information

4.3 Recorder

The descriptions of newsgathering in the extracts by Taylor and Higgins make reference to videotapes because, until recently, tape was the main storage medium used for video. Camcorders had a built-in VTR (videotape recorder) and in the first camcorders the video was recorded as an analogue signal. Camcorders used for ENG (electronic news gathering) now store the video as a digital signal, whatever medium is used for recording. Camcorders are now appearing which can store the digital video on DVDs or on memory cards.

Taylor (2004) compares DVD-based camcorders and memory-card camcorders in his updating paper. An extract from this follows.

[…]

[T]wo quite different solutions are competing for the TV news broadcaster's camcorder business:

  • DVD based camcorders

  • Solid state flash memory based camcorders

Ever since the development of the DVD, its potential as a rugged, compact, random access medium has made it attractive to TV news companies as an alternative to video tape for use in camcorders and also as an archive medium. It is not surprising therefore that at least one broadcast equipment manufacturer (Sony) is currently introducing camcorders and field players using the latest 'blue disk' DVD technology […] which offers approximately 27 GB recording capacity on a 120 mm disk. At 25 Mbps this provides about two and a half hours of recording. The hope is that the blue disks will soon be compatible with the DVD drives available in standard laptops thus facilitating convenient low cost field editing.

There are a few physical limitations with this solution due to the size of the disk, its susceptibility to vibration and unreliability of the disk burning process at low temperatures. However, careful design is minimising the impact of these limitations and a number of TV news organisations are changing over to DVD acquisition.

Even more exciting, last year [2003] Panasonic showed a prototype completely solid state camcorder (called P2 CAM) using four of the consumer SD [secure data] flash memory cards embedded in a standard PCMCIA package called the P2 card.[PCMCIA (Personal Computer Memory Card International Association) is an industry trade association that creates standards for the memory cards that slot into notebook computers and other small portable devices.] Using 1 GB SD cards each P2 card supplies an initial 4 GB memory capacity. The camcorder holds five P2 cards to give it a total recording duration at 25 Mbps video of about 90 minutes (allowing for audio channels and overheads). Clearly this camcorder totally overcomes the physical limitations which are inevitable with any mechanical recording system and it created enormous interest from the broadcast industry. It is now in production and being evaluated by a number of TV news companies.

The convenience of simply taking the P2 card out of the camcorder and slotting it directly into a laptop computer for editing and downloading to the station server system, via the Internet if necessary, was instantly appreciated. The Achilles' heel of this otherwise ideal solution is the cost of the SD media, but as experience indicates, the cost per Gigabyte of flash memory is reducing by a factor of around 4 per annum. It will not be too long before individual SD cards reach 16 GB capacity at affordable prices. Each P2 card would then be capable of storing nearly five hours at 25 Mbps – more than enough capacity to handle HD [high definition] TV at 100 Mbps! It is also worth noting that Panasonic point out that, unlike tape, the SD cards are 'non-consumables' lasting the life of the camera. Therefore only a relatively small number of cards are required for each camera as the content should be downloaded into station servers soon after shooting, thus freeing up the cards and making the cost of the medium unimportant.

When either, or both, of these new acquisition technologies replace video tape based camcorders over the next couple of years the migration of the TV news industry to IT technology will be complete. It will have been an extraordinary revolution in terms of its implementation speed having taken less than 10 years from servers and hard disk editing systems first attracting TV news companies' attention. Remarkably it is only around 25 years since Electronic News Gathering ousted film and ushered in the all electronic era.

Taylor (2004)

Tape, DVD and memory cards use three different physical principles for storing data (Figure 11), and have different merits and limitations.

Storage media
Figure 11 Storage media

Tape is a magnetic storage medium. In very general terms, data is stored by the orientation of the magnetic field in microscopic particles on the tape. The orientation is set when writing to the tape and detected when reading from it. Tape is cheap and can store large amounts of data, but has the significant disadvantage that it can only be written to and read from sequentially. It is not possible to jump to somewhere in the middle of the tape; you have to run through it to get there. Also, compared with DVDs and memory cards, tape is less robust. It can be quite easily damaged and wears out after repeated use.

A DVD is an optical storage medium. Data is written to it by putting microscopic marks on the surface of the disk. Data is read from it by detecting the presence of the marks, which is done by shining a laser onto the surface and measuring the amount of light reflected. Depending on the type of disk, writing to the disk may be permanent or reversible (for a DVD-RW, rewritable, disk). DVDs are now cheap and robust. Certainly data can be read from the disk any number of times with no significant degradation to the disk, and RW disks can be rewritten many times. DVDs do not need to be read serially like tape because it is possible to jump straight to anywhere on the disk – they are random access.

Memory cards use flash memory, which is an electrical storage medium, used in an increasing range of applications including digital (still) cameras. Microscopic cells in an integrated circuit can be set to a voltage and they remain at that voltage by holding electrical charge even when the power is disconnected, until deliberately changed. Some types of flash memory are random access, but others require sequential access. Writing to and reading from memory cards is faster than with a DVD.

Whereas a tape has to be moved physically through a VTR, and a DVD is spun around as the read/write 'head' moves across the disk, there are no moving parts involved in using a memory card. This is what Taylor is referring to when he says they are solid state. Generally speaking, moving parts are more prone to wear and tear and failure, so solid state components tend to be more reliable and last for longer. The equipment for reading and writing to flash memory is therefore more rugged than that for tapes and DVDs.

Activity 16

Using information from the above discussion, answer the following questions about tape, DVDs and flash memory.

  1. Which allow random access when reading?

  2. Which is solid state?

Discussion

  1. DVD and some types of flash memory allow random access, but tape does not. Tape is written and read sequentially.

  2. Flash memory is solid state. Tape and DVDs require moving parts to read and write data.

Taylor makes extensive use of approximate calculations on memory sizes, data rates and recording durations in the extract. It is instructive to 'unpick' some of his calculations.

Taylor says that the 27 GB (gigabyte) capacity of the blue disk DVD provides about two and a half hours of recording at 25 Mbps (mega bits per second). A gigabyte is about 1,074,000,000 bytes and there are eight bits in a byte, so 27 GB is about:

(to three significant figures).

One gigabyte is actually 230=1,073,741,824 bytes, but I don't need all the figures because I only want the answer to three significant figures.

At 25 Mbps this is enough storage for:

Dividing by 60 for the number of seconds in a minute gives 155 minutes, which is indeed 'about two and a half hours'.

About the P2 cards Taylor says:

four of the consumer SD [secure data] flash memory cards [are] embedded in a standard PCMCIA package called the P2 card. Using 1 GB SD cards each P2 card supplies an initial 4 GB memory capacity.

Taylor (2004)

This is simply saying: 4×1 GB = 4 GB

Taylor then says:

The camcorder holds five P2 cards to give it a total recording duration at 25 Mbps video of about 90 minutes (allowing for audio channels and overheads).

Taylor (2004)

Five P2 cards will store 5×4 GB = 20 GB. That is 20 gigabytes which using a similar calculation to the one we did above, is about 1.72×1011 bits. At 25 Mbps that is enough for:

Dividing by 60 for the number of seconds in a minute gives about 115 minutes. That is rather more than the 90 minutes that Taylor estimates, but we have not taken account of the audio coding or any overheads (Overheads are extra bits that are needed to manage the data – file names, bits to keep the video and audio synchronised, etc.) We don't have any information on how much should be allowed for these other factors, but it seems reasonable that they could account for the difference.

Later, Taylor says:

It will not be too long before individual SD cards reach 16 GB capacity at affordable prices. Each P2 card would then be capable of storing nearly five hours at 25 Mbps – more than enough capacity to handle HD TV at 100 Mbps!

Taylor (2004)

If an SD card stores 16 GB, then a P2 card (which holds four SD cards) can store 4×16 GB=64 GB. Using Taylor's claim that 20 GB is enough for about 90 minutes, 64 GB should be enough for about:

Dividing by 60 for the number of minutes in an hour, that is 4.8 hours, which is 'nearly five hours', as Taylor says.

Activity 17

Based on Taylor's statement:

Each P2 card would then be capable of storing nearly five hours at 25 Mbps – more than enough capacity to handle HD TV at 10 Mbps!

Taylor (2004)

approximately what duration of HD TV should a P2 card be capable of storing?

Discussion

We are told that a PCMCIA card can store five hours at 25 Mbps and that HD TV (high-definition television) runs at 100 Mbps, which is four times the data rate. This indicates that a PCMCIA card should be able to store 5/4 hours, which is 1 hour and 15 minutes, of HD TV.

T175_8

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