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
Email: james@gp2u.com.au
Web: https://gp2u.com.au/

ADSL Speed, Data Use, Contention Ratio

Speed

When it comes to video conferencing the primary determinant of picture and sound quality is the capacity of the "pipe" that joins the two sites.

A commonly quoted magic number is a capacity of > 384 kb/s (kilo bits per second) in each direction, with more being better. So if you have a 2 Mb/s (mega bits per second) ADSL line you should be right? Right?

Perhaps. ADSL stands for Asymmetric Digital Subscriber Line. The asymmetry refers to the fact that the download speed is much faster than the upload speed.

Most of the time this does not matter as we do a lot more downloading than uploading, however for video conferencing upload speed is critical, because it is upload speed that determines how good the picture will be at the other end of the connection.

You can test your connection using one or more of the speed testers gathered together here: https://gp2u.com.au/static/links.html

Data Use

So how much data do you use? 1 Byte contains 8 bits so 384 kb/s is close enough to 50 kB/s (kilo bytes per second) - and we use that much data in 2 directions making a total of 100 kB/s. 3600 seconds in an hour gives us minimum use rates of 360 Mega Bytes (0.36 Giga Bytes) per hour.

Although it depends on the software/hardware configuration most video conferencing equipment will happily use substantially more data than this (unless specifically configured not to). A data use budget of 0.5-1 Gig per hour is a good real world ball park.

Contention

The way cheaper ADSL providers manage to be cheaper and still make a profit is by selling the same chunk of capacity to more people. This is called the contention ratio.

If you have wireless ADSL at home and have kids you will have seen contention in action as you connection grinds to a halt while your kids simultaneously stream music, Skype friends and inbox frenemies on Facebook - they are competing for limited capacity. If you use the same provider as your neighbour it might not even be your kids slowing your connection down.....

Dr James Freeman

GP2U Telehealth
173 Macquarie Street
Hobart 7000
Mobile: 0438 350 854
Email: james@gp2u.com.au
Web: https://gp2u.com.au/