Fmtconv is a format-conversion plugin for the Vapoursynth video processing engine. It does:
* Resizing.
* Bitdepth conversion with dithering.
* Colorspace conversion (matrix, transfer characteristics and chromatic adaptation).

It supports:
* Pixel data types: 8-–12-, 14- and 16-bit integer, 32-bit float.
* Colorspaces: RGB, Y, YUV in 4:4:4, 4:2:2, 4:2:0, 4:1:1 and YCgCo with the same chroma subsampling factors.
* Progressive and interlaced content.

Fmtconv is focussed primarily on quality and exactness rather than execution speed.
This does not mean it is slow or unoptimized, but fmtconv is clearly not on par with the fastest equivalent 8-bit filters.