@HolyWu, I built LSMASHSource from your repo using
this CMake file taken from @MeteorRain repo. When tested for seeking issues with
that file my build has errors but your build is fine. Something wrong with my building process? ffmpeg 4.2.1 / 4.3 used without difference.
There is patch for replacing avresample with swresample in your repo but avisynth exlibs - #pragma comment( lib, "libavresample.a" ).