An output driver gives you access to the one filtered value per pixel, after a bucket has been completely rendered. You can use drivers for example to write to new image file formats, or to send pixels to a display device, to an application's window, etc.
You can specify a driver in an .ass file like this:
You can also specify multiple drivers for different AOVs, potentially using different filters and data types:
The implementation of a sample driver that writes out to a file a list of all the objects in a pointer AOV would look like:
For the above driver, we need to choose the correct output AOV to feed data to the driver. Here is an example .ass file that sets up a simple cube and the driver to output the object AOV to a file
The output of the driver will then print something like the following to the output file name.