[Linphone-developers] problem with ndk-build

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when I  execute command : ndk-build

I have this message of error : 

Build X264 plugin for mediastreamer2
Compile thumb  : ortp <= ortp.c
jni/..//submodules/linphone/oRTP/build/android/../..//src/ortp.c:41:23: fatal error: srtp/srtp.h: No such file or directory
compilation terminated.
make: *** [obj/local/armeabi-v7a/objs/ortp/src/ortp.o] Error 1

Someone can help me !!

Thank