Friday, October 14, 2011

Video Conferencing 101

Video conferencing is actually a pretty old technology, and really dates back to the beginnings of television. Although it’s been in constant evolution for decades the revolution happens when high speed Internet meets cheap computing power.

Moving pictures are created by displaying many static images rapidly in sequence. Humans can process 10 to 12 separate images per second, perceiving them individually. Once this rate is exceeded the illusion of continuous movement is created. The early silent movies operated at 14 frames (images) per second (FPS). Modern TV and movies use 24-30 FPS.

When we look at the quality of a video image the detail in each of the images is just a important as FPS. Picture detail is typically quoted in terms of pixels, where one pixel is one “dot” that can be a specific colour. The more pixels you have the better the picture will look, and the larger you can blow it up before you begin to notice individual pixels. To put things in perspective here are some common horizontal x vertical pixel resolutions

iPhone 3 480x320

iPhone 4 960x640 (note 4 times as many pixels, but same size screen)

VGA 640x480 (probably what you had with your first computer monitor)

PAL TV 720x576 (standard Australian analogue TV)

XGA 1024x768 (any modern computer monitor will equal or exceed this)

HD Video 1280 x 720 (720p)

HD Video 1920 x 1080 (1080p)

So with video the more pixels we have, and the higher the frame rate, the better the picture we see will be.

There is however a very simple mathematical reality:

Data cost = FPS x Horizontal Pixels x Vertical Pixels

While a number of clever techniques, falling under the broad umbrella of compression (like zip files) can be used to reduce the data cost no one has a magic bullet that lets them compress video data much better than anyone else. In fact most companies use exactly the same techniques. You should probably read the last two sentences again.
Video conferencing technology works like this.

Connect a camera, monitor, microphone and speakers to a computer

Take lots of pictures every second

Convert and compress the pictures/audio into a stream of 0s and 1s using a piece of software called a codec.

Send that data stream over the Internet to another computer using a communication protocol.

During transmission over the Internet this data stream can be protected from eavesdropping by using encryption

Reverse the process at the recipient computer by using the same codec to convert the data stream back into pictures and audio for output via a monitor and speakers

Do that on both ends and the same time and there you have it – a videoconference.

In part 2 we will unravel codecs, protocols, and encryption.....

Dr James Freeman
GP2U Telehealth
173 Macquarie Street
Hobart 7000
Mobile: 0438 350 854


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