Technical standards for linking access control and video do not exist. The Security Industry Association has been working on writing standards, and announced the Open Systems Integration and Performance Standards - Digital Video Interface Data Model which specifies interface requirements for the digital video component of a video surveillance solution. But there is a long way to go before integration standards between the two systems are completed.
Also, every DVR / NVR manufacturer's Software Developers Kit (SDK) is completely different though most offer very similar features. It should be noted that some manufacturers have several SDKs, so care needs to be taken to check which specific items of equipment can and cannot be integrated together.
Organizations will demand truly integrated solutions. Security systems and security guards will become a more integrated function, and intelligent video analytics will add a new layer of security for an organization. Video will become proactive and less of a forensic, after the event, analysis tool. Video as part of a deeply integrated solution will increasingly stop crime and not just report on it. Deeply integrated access control, video management, and video analytics will help create the truly integrated systems of tomorrow.