Add missing SWS_SPLINE interpolation (#2188)

Author: lgeiger

av/video/reformatter.py

@@ -17,7 +17,8 @@ class Interpolation(IntEnum):
     BICUBLIN: "Luma bicubic / chroma bilinear" = SWS_BICUBLIN
     GAUSS: "Gaussian" = SWS_GAUSS
     SINC: "Sinc" = SWS_SINC
-    LANCZOS: "Bicubic spline" = SWS_LANCZOS
+    LANCZOS: "3-tap sinc/sinc" = SWS_LANCZOS
+    SPLINE: "Cubic Keys spline" = SWS_SPLINE
 
 
 class Colorspace(IntEnum):