Prebuilt opencv static library for opencv_dart to speedup compile
- prbuilt ffmpeg for android macos ios are from avbuild (https://github.com/wang-bin/avbuild)
- prebuilt ffmpeg for linux and windows are from https://github.com/BtbN/FFmpeg-Builds
- https://github.com/obsproject/obs-studio/blob/master/cmake/finders/FindFFmpeg.cmake
- https://github.com/Kitware/VTK/blob/master/CMake/FindFFMPEG.cmake