The first public version of Dualsub was released on 2018-09-17, and it has been almost 3 years now. In the beginning, Dualsub is a simple subtitle extension that only supports YouTube, but now it is a feature-rich subtitle extension that supports many video wesites. The developer have spent a lot of energy in it. It has always been a completely freeware. In order to be worth spending more energy on development and maintenance in the future, some features have now been changed to paid features.
You can think of Dualsub as consisting of two parts:
api.dualsub.xyz operated by the developer.The server provides natural language processing services that can be used by all video websites, such as machine translation, Chinese analysis, and Japanese analysis. To operating the server, the developer need to pay for the cloud service providers every month. If you are using server-side features, then you are better to pay for these features as well. So from now on, server-side features are paid features.
The client is still feature-free, and there is no paid version and free version.
The business model is a subscription model. Users pay monthly, and can use server-side features during the subscription period.
Users will get an API Key, which is a randomly generated string, such as b51bd887-0844-4c19-9149-c776cc8127f9.
An API Key can only be used by a single user in a fair situation, and the API Key cannot be made public or shared with others.
For YouTube, you can use the "Simple Mode", the "machine translation" in this mode will directly use YouTube's translation data without relying on the Dualsub server.