Using brew install ffmpeg, ffmpeg is running fine on my Mac,

$ ls -l /usr/local/bin/ | grep ffm
-rwxr-xr-x 1 jpm admin 20686092 Dec 16 13:31 ffmpeg

However when I swift build:

$ swift build
Linking ./.build/x86_64-apple-macosx10.10/debug/SwiftFFmpegDemo
ld: warning: Could not find auto-linked library 'swresample'
ld: warning: Could not find auto-linked library 'avutil'
ld: warning: Could not find auto-linked library 'avfilter'
ld: warning: Could not find auto-linked library 'avcodec'
ld: warning: Could not find auto-linked library 'avformat'
ld: warning: Could not find auto-linked library 'swscale'
Undefined symbols for architecture x86_64:
"_av_buffer_alloc", referenced from:
_$S11SwiftFFmpeg8AVBufferC4sizeACSgSi_tcfc in AVBuffer.swift.o
(and many Undefined symbols errors like that)

What to do?? thanks!