Emblaze-VCON xPointS User Manual download pdf (Page 26)

The advantage of transcoding is connection flexibility, and in the ideal world all sessions would support

full transcoding. However, transcoding requires additional processing power and can also cause

additional call latency (delay). Depending upon the MCU and the operating mode (see below),

transcoding support varies from very limited (perhaps connection rate only) to advanced.

Screen Layouts – MCUs typically support three different screen layout modes; full screen, continuous

presence, and a combination of the two. In full-screen mode (often called voice activated switching or

VAS), the MCU sends a full-screen view of the video image from the currently speaking system to all

participating sites. In continuous presence mode (also called CP or quad-screen mode), the MCU

combines the incoming video signals together to create a new signal that includes video images from

multiple locations. The result is that several (or perhaps all) of the participating sites are on screen (or

present) continuously. Finally, hybrid mode involves adding voice activated switching to a single

window within a continuous presence layout.

It is worth pointing out that full screen conferences can either be non-transcoded or transcoded, but

continuous presence sessions are typically transcoded.

Full Screen

View

Continuous Presence

(CP) View

Figure 18: Comparison of Full Screen and Continuous Presence Layouts

Number of Encodes Supported – In order to host a multipoint video call, an MCU must

i) receive (or decode) the incoming video signals, and ii) create (or encode) the signal (or signals) to be

sent to the participating sites, and iii) transmit the newly created (encoded) signals. The number of

encodes an MCU can provide determines the number of different signals that can be sent to the

participating endpoints.

For example, a single-encode MCU is able to create only one output signal per conference, and thus ALL

participating endpoints will receive the same exact video image (typically at the same speed, using the

same protocol) from the bridge. Such a situation forces the participating endpoints to use the same

connection speed and/or protocols – regardless of whether or not that represents the best possible

connection profile for each system. On the other hand, an MCU that supports universal encoding is able

to create an individual signal (encode) that is best suited for each participating system.

Evaluation of the Emblaze-VCON VCBPro Video Bridge

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Emblaze-VCON xPointS User Manual Page 26