xbrz filters 4x and above work as described.
xbrz filters 4x and above only seem to work with opengl, but for the simple video driver stutters.
Use the simple driver and select the filter.
Operating System (Windows, Mac, Linux, etc.): All Platforms
Interface (wx and SDL, default is wx): wxWidgets
Version of code (pre-built binary version, or commit ref, or just "master"): current master
Any other relevant build information:
If this is e.g. a joystick or video issue, then the relevant hardware information: