I’ve been getting a lot of questions from various places that deal with how video conferencing looks and feels, and mainly inquire about the difference between CP and VAS.
So – What do CP and VAS mean, and what do they have to do with video conferencing?
VAS is short for Voice Activated Switching. This basically means that the active speaker, the term for the meeting participant that is now talking, will be seen by all meeting participants whenever she (or he) is talking.
This means that during a call of let’s say 4 participants – David, James, Susan and Heather – if David is now speaking, everyone will see David on the screen:
If, for instance, James will now start talking, he will replace David on the screen:
In more advanced systems James might see David (the “last active speaker”), while everyone else will see James. This is known as a “no self-see” option, where a participant will not see herself, which some see as a physiological downside.
A voice activity detection algorithm (VAD for short) is usually used to determine which of the meeting participant is currently speaking, and sometimes another component (mixer) takes care of comparing a few “talking” participants and deciding who is the “active” one.
CP is short for Continuous Presence. This basically means that all participants, or a subset of these participants, including the active speaker, are seen on the screen at the same time.
In our example above this means that all 4 participants may be seen on screen:
Left: a 2×2 CP layout. Right: a 1+3 CP layout.
CP also involves identifying the active speaker, as in some cases (like the 1+3 layout above) the “active speaker” will move to a designated sub-frame, be shown in a larger sub-frame or any other graphical way to emphasize they’re the one who’s talking.
CP involves a lot of graphical manipulations on the streams received by the different endpoints, including scaling and mixing the images. Today, with SVC technology, CP can be achieved without graphical manipulations, but only in closed H.264-based deployments, which are still not common.
VAS, CP and Video Conferencing
CP is basically the evolution of VAS when it comes to video conferencing. A while back, when there was not enough CPU to do the graphical manipulations necessary for CP, and when the screen size was too small for a CP layout, VAS was the best solution. In fact, if you look at what most UC clients are doing with conferencing, they are still using VAS as their means of displaying multiple participants in a conference scenario.
With the introduction of larger screens and greater conferencing platforms, CP became not only relevant but very popular. On today’s HD screens the latest RADVISION Elite MCU can show up to 28 participants in one high definition layout, and the result is quite amazing. As you can see below:
On the other hand, as video conferencing is making its way to desktops, mobile handsets and other handheld devices, and as everything goes to the cloud, CPU power is again a relevant factor, and I believe VAS can, and should, provide a viable and cost-effective mode of operations.
So what should you use for your video conferencing service, VAS or CP? It all depends, I guess, on the type of devices and the type of infrastructure that you want to roll out, and the exact user interface you want to provide. As explained above both make for great user experience with excellent market-proven examples out there.