vout: warn when we get less display pictures than requested

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

src/video_output/vout_wrapper.c

@@ -130,9 +130,15 @@ int vout_InitWrapper(vout_thread_t *vout)
     const unsigned reserved_picture = DISPLAY_PICTURE_COUNT +
                                       private_picture +
                                       kept_picture;
-    picture_pool_t *display_pool =
-        vout_display_Pool(vd, allow_dr ? __MAX(VOUT_MAX_PICTURES,
-                                               reserved_picture + decoder_picture) : 3);
+    const unsigned display_pool_size = allow_dr ? __MAX(VOUT_MAX_PICTURES,
+                                                        reserved_picture + decoder_picture) : 3;
+    picture_pool_t *display_pool = vout_display_Pool(vd, display_pool_size);
+#ifndef NDEBUG
+    if ( picture_pool_GetSize(display_pool) < display_pool_size )
+        msg_Warn(vout, "Not enough display buffers in the pool, requested %d got %d",
+                 display_pool_size, picture_pool_GetSize(display_pool));
+#endif
+
     if (allow_dr &&
         picture_pool_GetSize(display_pool) >= reserved_picture + decoder_picture) {
         sys->dpb_size     = picture_pool_GetSize(display_pool) - reserved_picture;