Why use video/audio in communication systems?

E-mail, videoconferencing, videophones, audio conferencing, ...., multiple technologies can be used to disseminate information, and it has been shown that video is the most effective system.

It has been demonstrated that as individuals we retain:
  · 10% of what we read
  · 20% of what we hear
  · 50% of what we see and hear

It is clear that video should therefore be used for communicating in:
  · Company training for partners and employees
  · Training of travelling sales force networks
  · Corporate communication in general
  · Publicity, ...

In short, to get the best out of it, video should be used for sharing knowledge and information, and also when we wish to influence a particular audience. A system should be used which allows us to ensure that the audience receives and retains the content (for instance, if we publish information on a website, we cannot be sure whether the target audience has received the information).

With the development of audio and video, and the arrival of the internet, an attempt has been made to make one of mankind's dreams come true, namely videoconferencing, the transmission of multimedia over the internet. Many of us have seen futuristic films in which conversations are carried on through a screen.

How is video provided over a network?

What would a videoconference system be without video? Communicating with another person by voice is something that works quite well, and in fact this is what we do when we make a telephone call. Yet if we add video to this, we achieve the ideal communication system. The advantage of videoconferencing is that it is as easy as making a phone call, while allowing face to face communication, in other words, more effective communication.

Various possibilities:

  1. BROADCAST: This can best be defined as the sending of information from one point to various other points. "Open to all" means our broadcasts reach a worldwide audience, i.e. they are available for all those wishing to receive them.

  2. VIDEO ON DEMAND= UNICAST. From one point to another point, i.e. sending information from one IP address to another IP address. In this way the message is sent to a single person, directly to that computer.

  3. MULTICAST = Live, bi-directional communication, sending information to various locations at the same time (video in the case of videoconferencing). Here we transmit to a series of people, normally in one domain (a group of computers with a more or less similar IP).

Both broadcasting and multicasting have a lot in common, the difference between them being the range of transmission (the number of routers through which the packets have to pass; the "ttl" number as it is known).

What bandwidth do I need?

VIDEO QUALITY	VIDEO FORMAT	BANDWIDTH
Broadcast	MPEG2	2-10 MHz
VCR/Corporate	MPEG1	0.5-1.5 M
Variable	MPEG4	32 K-1.5 M

What video quality does my application require?

Different video formats:

  AVI: Microsoft's AVI format consists of compressed video, without master frames, but with re-scalable compressed frames, with which we can vary the size of the image. The quantity of information recorded depends on the quality, i.e. the higher the quality, the greater the amount of information recorded. Not really suitable for real time transmitting.

  MPEG: MPEG2 is the method currently used for transmitting all digital channels. The MPEG format is identical to the audio one, reducing not by mathematical formulae but by the characteristics of the human eye. The signal can be reduced by up to 40 or 50% without us hardly noticing it. The MPEG4 format (and the coming one, which will be MPEG7) not only takes the aforementioned into account, but, depending on where things are situated in the image, it will modify it when compressing it, by inventing what it does not see. I.e., if we film a person, and it is the master frame, when this moves, we only send the changes in the image (the movement of the person and what is behind him or her), but with the new format, what is behind will be invented, will be predicted, in this way enabling the frames to be reduced even further.

QUALITY LEVEL	VIDEO FORMAT	TRANSMISSION SPEED
Critical (Broadcast)	MPEG2	Higher quality = Slower
Ad hoc	MPEG1	Faster
“BEST EFFORT”	MPEG4	Faster

What does a video signal need to be a good quality one?

   · Bandwidth
   · Absence of flicker
   · Absence of delay
   · Absence of jitter (variation = flicker)