You can escalate an IM to a call and then merge additional particpants into it through CUPC. If these participants are video-capable, CUPC will offer video functionality automatically. Note that CUPC 7.x only support video in softphone mode. Deskphone mode would require CUVA.

CUCM would choose the appropriate conference bridge when CUPC requests a conference be formed for three or more participants. The Intelligent Bridge Selection would choose a video bridge if two or more of these participants are video capable.

CUVC is the MCU which would provide the video conference resource to UCM. This is analogous to the audio conferencing resource provided by DSPs in an ISR.