sudo apt-get install  X11proto-core-dev
x11proto-xext-dev is already the newest version.
x11proto-xext-dev set to manually installed.

/configure --prefix="$DIST_DIR/ffmpeg_build" --extra-cflags="-I$DIST_DIR/ffmpeg_build/include --static"    --extra-ldflags="-L$DIST_DIR/ffmpeg_build/lib" --bindir="$DIST_DIR/bin" --extra-libs="-ldl -static" --enable-gpl    --enable-libass --enable-libfdk-aac --enable-libmp3lame --enable-libopus --enable-libtheora    --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-x11grab   --disable-shared --disable-debug --enable-static
ERROR: Xext not found