Warn about vf_mp

libavfilter/vf_mp.c

@@ -732,6 +732,11 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
     char name[256];
     int i;
 
+    av_log(ctx, AV_LOG_WARNING,
+"This is a unholy filter, it will be purified by the ffmpeg exorcist team\n"
+"which will change its syntax from dark -vf mp to light -vf.\n"
+"Thou shalst not make spells or scripts that depend on it\n");
+
     m->avfctx= ctx;
 
     if(!args || 1!=sscanf(args, "%255[^:]", name)){