PSIA (Physical Security Interoperability Alliance) was an industry effort to standardise interoperability across physical-security devices — cameras, recorders, access control — using a REST/HTTP style of API. It emerged around the same time as ONVIF with a similar goal: free integrators from per-vendor protocols. In the video space, however, ONVIF won broad adoption, and PSIA's video interoperability work is now largely historical, though its ideas influenced later REST-style device APIs.
Knowing PSIA exists matters mostly for context and for legacy systems. It explains why ONVIF is not the only interoperability standard you may encounter in older documentation or installed bases, and it frames a useful point: interoperability "standards" are only as real as their adoption. A standard with few conformant products does not buy you interoperability in practice.
The pitfall is treating any interoperability claim — PSIA, ONVIF, or a vendor's own "open API" — as a guarantee of plug-and-play. The practical questions are which standard, which version/profile, and how many shipping products actually implement it. For new video deployments, ONVIF (with the right profiles) is the live standard to design around; PSIA is relevant chiefly when integrating or migrating older equipment that predates ONVIF's dominance.
