Firstly, mathops.h is a private header of libavcodec and should not be used
in fftools. It may reference libavcodec internal symbols, causing link
error with dynamic library, e.g.,
fftools/ffmpeg_filter.c:2687: undefined reference to `ff_rv_zbb_supported'
Secondly, mid_pred operates on int types, while current use case is
int64_t.