Google made the change from Google Talk video to Google Hangouts video calls earlier this year to improve reliability. Users are now no longer able to receive calls from legacy Google Talk video services. These services include video chat from old Android Google Talk clients and third-party services that make video calls to Google Talk users. Any video calls initiated from legacy Android Google Talk applications will not succeed and the user will see an error message.
Hangouts video calls open in it's own window, and allow higher video quality during calls. With Hangouts video calls, users also have the option of using the Google+ Hangout features. A Google+ account is not required to make a 1-to-1 video call. Users who do have a Google+ account do not need to make any changes to their account configuration in order to continue to make video calls.