AC_MSG_ERROR([cannot find ${real_ffmpeg_tree}/libavcodec/libavcodec.a, make sure you compiled libavcodec in ${with_ffmpeg_tree}])
fi
if ! grep -q "pp_get_context" "${real_ffmpeg_tree}/libavcodec/libavcodec.a"; then
if ! fgrep -s "pp_get_context" "${real_ffmpeg_tree}/libavcodec/libavcodec.a"; then
dnl The given libavcodec wasn't built with --enable-pp
AC_MSG_RESULT(no)
AC_MSG_ERROR([${real_ffmpeg_tree}/libavcodec/libavcodec.a was not compiled with postprocessing support, make sure you configured ffmpeg with --enable-pp])