Basically, here is how to do:
- put the library in the same folder as your program (under Windows, on Linux the library is already installed)
- add BGRABitmap to your project
- write the code to convert
In the code, create a TBGRABitmap from unit BGRABitmap, do LoadFromFile with the source and SaveToFile with the destination. It will guess from extensions the file format.
If you want to specify parameters for the writer, you need to create a TBGRAWriterWebP from unit BGRAWriteWebP and set its properties and add it as an additional parameters to SaveToFile.