docs: update design docs

docs/design/part-buffer.txt

@@ -29,7 +29,7 @@ When a Buffers is writable as returned from gst_buffer_is_writable():
  - metadata can be added/removed and the metadata can be changed
  - GstMemory blocks can be added/removed
 
-The individual memory blocks have their own refcounting and READONLY flags
+The individual memory blocks have their own locking and READONLY flags
 that might influence their writability.
 
 Buffers can be made writable with gst_buffer_make_writable(). This will copy the

docs/design/part-bufferpool.txt

@@ -132,11 +132,19 @@ Allocation query
 
       It is also possible to configure the allocator in a provided pool.
 
-  (out) "metadata", G_TYPE_ARRAY of GType
-        - an array of metadata API types that can be accepted.
+  (out) "metadata", G_TYPE_ARRAY of structure
+        - an array of metadata params that can be accepted.
+
+      struct {
+        GType api;
+        GstStructure *params;
+      }
+
+      Use gst_query_parse_nth_allocation_meta() to get the values.
 
       These metadata items can be accepted by the downstream element when
-      placed on buffers. 
+      placed on buffers. There is also an arbitrary GstStructure associated
+      with the metadata that contains metadata specific options.
 
       Some bufferpools have options to enable metadata on the buffers
       allocated by the pool.

docs/design/part-meta.txt

@@ -9,8 +9,6 @@ negotiated in the bufferpools.
 
 Some examples of metadata:
 
- - timestamp, duration
- - offset, offset_end
  - interlacing information
  - video alignment, cropping, panning information
  - extra container information such as granulepos, ...