lavc: Improve thread locking error message

libavcodec/utils.c

@@ -1050,7 +1050,10 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
 
     entangled_thread_counter++;
     if (entangled_thread_counter != 1) {
-        av_log(avctx, AV_LOG_ERROR, "insufficient thread locking around avcodec_open/close()\n");
+        av_log(avctx, AV_LOG_ERROR,
+               "Insufficient thread locking. At least %d threads are "
+               "calling avcodec_open2() at the same time right now.\n",
+               entangled_thread_counter);
         ret = -1;
         goto end;
     }