编译ffmpeg出现pkg-config: command not found

系统版本：ios10.7.5
x_code：4.3
sdk：5.1
Last login: Mon Nov 19 16:21:54 on ttys000
aamatoMacBook:~ aa$ cd /Users/aa/Desktop/ffmpeg4ios-master 
aamatoMacBook:ffmpeg4ios-master aa$ ./configure --disable-doc --disable-ffmpeg --disable-ffplay --disable-ffserver --disable-avdevice --disable-swscale --disable-avfilter --disable-avformat --disable-debug --disable-encoders --enable-cross-compile --disable-decoders --disable-armv5te --enable-decoder=h264 --enable-pic --arch=arm --target-os=darwin --cc=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/llvm-gcc --as='gas-preprocessor.pl /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/llvm-gcc' --sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk --cpu=cortex-a8 --extra-cflags='-arch armv7' --extra-ldflags='-arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk'
./configure: line 764: pkg-config: command not found
install prefix            /usr/local
如何解决pkg-config 求大神赐教，万分感激！