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Chapter 6 - Operations Performed During On Going Conferences
6-72
Broadcasting Annex D Still Video Image (Slide)
An endpoint with Annex D capabilities can send an Annex D still video
image (slide) to the MCU to be broadcast to all other participants in a
Transcoding or a Continuous Presence video conference.
When an endpoint sends the Annex D image, the following operations are
performed by the MCU:
• The MCU automatically switches the video layout to Full Screen (1x1)
• The MCU video forces the sender to be seen by all participants when an
MCV (Multipoint Command Visualization) signal is sent from the
endpoint
• The MCU transmits the Annex D image in full 4CIF quality to all the
connected conference participants
An Annex D slide can be transmitted by an endpoint using one of the
following methods:
• The endpoint first requests the chair token and becomes the chairperson.
Sometimes during the conference, while acting as the chairperson, the
endpoint may send the Annex D still image.
• The endpoint sends an MCV signal to the MCU requesting the
Chairperson. If the request is accepted by the MCU, the endpoint
becomes the chairperson and transmits the still image. To release the
Chair token and restore the conference to its previous state the Cancel-
MCV command is sent by the endpoint. This procedure conforms to the
H.320 standard.
• The endpoint sends an Annex D image without an MCV signal, or a
request for the chair token prior to the image transmission. The MCU
recognizes the incoming Annex D image, processes it and broadcasts it
to all other participants. In such a case, only the participants who can
view the sender can see the Annex D still image.
The Annex D image is sent to all endpoints. If an endpoint has two screens,
the still video image is viewed on one screen while the live video will be seen
on the second screen, without being interrupted. If the endpoint has only one
screen, the live video is interrupted for a few seconds to display the still
image. The image is stored in the endpoint’s memory and can be viewed at
the discretion of the individual participants. At the end of the transmission,
the conference video is restored.