Here's a wonderful tutorial on how to do digital resampling and interpolation in general.
You'll also find, within the rtl directory, examples of a nearest
neighbour interpolator, a
linear upsampling interpolator,
and a quadratic upsampling interpolator.
All three have been discussed on the ZipCPU blog:
the nearest neighbour interpolator
here,
the linear interpolator
here,
and the quadratic interpolator
here.
If time permits, I look forward to adding some higher order interpolation solutions and/or splines to this repository.
The tutorial is offered here under the Creative Commons, Attribution-NoDerivations 4.0 International license.
The Verilog source code and software (if any) are released under the GPLv3.
If these conditions are not sufficient for you, other licenses terms are available for purchase.