OBS Studio can be extended through the use of plugins, scripts, and via WebSocket.
OBS Studio has a rich collection of user-developed plugins that provide additional functionality to the core program. For more information on plugins, see the Plugins Guide.
These are typically implemented in C++ and compiled into dynamic libraries that are loaded when OBS Studio starts up. The main advantage of a plugin is high performance and raw access to OBS Studio's functions and libraries.
On the other hand, developing plugins requires setting up an environment for compiling OBS Studio, and being able to deal with subsequent versions that may require your plugin to be recompiled. You must also consider how your plugin will run on platforms other than the one on which you develop.
For more details on setting up a development environment, see Getting Started with OBS Studio Development on the wiki.
To learn about the core API, see the API Reference in the developer documentation.
Scripts can provide additional functionality, especially for interacting with scenes and sources. They can be written in Python or Lua, with APIs based closely on the OBS C API.
The advantage of writing scripts is that they are simpler to develop, mostly platform-independent, and scripts are usually resilient to minor changes in the OBS C API. On the other hand, they are less performant than plugins; however, in most cases, the performance difference is not an issue.
For more information on using and developing scripts, see the Scripting Guide.
Connecting to the built-in WebSocket endpoint allows for interacting with OBS Studio from external applications and scripts. For more details on enabling WebSocket, see the Remote Control Guide.