You would need a Cisco Telepresence Content Server (TCS) for recording video conference session.
http://www.cisco.com/c/en/us/products/collateral/conferencing/telepresence-content-server/data_sheet_c78-626482.html?cachemode=refresh
Treat the TCS as one participant in the video conference to record the session. Make sure your VX-TACTICAL have a multisite capablity (LIC-SX20-MS option key installed) to be able to record the ongoing session.
For example scenario in a point to point video conference call, to record the session add the TCS in the call to record the ongoing video call session (2+1). This will utilized the multisite feature of your VX-TACTICAL. While recording you can add another one participant in the call to utilized the max. multisite capability of the VX-TACTICAL (3+1).
To record just dial the IP address of the TCS using H323 standalone setup. The TCS can also initiate recording by dialing the IP address of your VX-TACTICAL.
SIP is also supported as long as you have call control (VCS/CUCM). When using SIP, recording can be initiated from endpoint by dialing the registered SIP recording number of the TCS. The TCS can also initiate recording by dialing the endpoint's SIP address.
For more info: http://www.cisco.com/c/en/us/td/docs/telepresence/tcs/6_0/administration/guide/tcs_6_0.pdf
regards,
Acevirgil