Fix ffmpeg build?

ffmpeg/Makefile

@@ -75,8 +75,9 @@ ffmpeg_impl:
 	pushd ffmpeg && git checkout n3.1
 	#git checkout 71052d85c16bd65fa1e3e01d9040f9a3925efd7a # or my muxing code won't work, they've modified the example since fba1592f35501bff0f28d7885f4128dfc7b82777
 	pushd ffmpeg && \
-	./configure --cxx=$$(which c++) --enable-static --enable-shared --enable-libx264 --enable-gpl --disable-swresample --prefix=$$(realpath $$PWD/../ffmpeg_out) && \
-	make -j $$(nproc) && \
+		./configure --cxx=$$(which c++) --enable-static --enable-shared --enable-libx264 --enable-gpl --disable-swresample --prefix=$$(realpath $$PWD/../ffmpeg_out) && \
+	    sed -i.bak 's/HAVE_ARC4RANDOM 1/HAVE_ARC4RANDOM 0/g' ./config.h && \
+		make -j $$(nproc) && \
 	make install
 
 package-ubuntu1804: