buffer: add peek_memory method

Add a peerk_memory method that simply fetches the memory at an offset without
refcounting or merging.

gst/gstbuffer.c

@@ -772,6 +772,33 @@ _get_mapped (GstBuffer * buffer, guint idx, GstMapInfo * info,
   return mem;
 }
 
+/**
+ * gst_buffer_peek_memory:
+ * @buffer: a #GstBuffer.
+ * @idx: an index
+ *
+ * Get the memory block at @idx in @buffer. The memory block stays valid until
+ * the memory block in @buffer is removed, replaced or merged, typically with
+ * any call that modifies the memory in @buffer.
+ *
+ * Since this call does not influence the refcount of the memory,
+ * gst_memory_is_exclusive() can be used to check if @buffer is the sole owner
+ * of the returned memory.
+ *
+ * Returns: (transfer none): the #GstMemory at @idx.
+ */
+GstMemory *
+gst_buffer_peek_memory (GstBuffer * buffer, guint idx)
+{
+  guint len;
+
+  g_return_val_if_fail (GST_IS_BUFFER (buffer), NULL);
+  len = GST_BUFFER_MEM_LEN (buffer);
+  g_return_val_if_fail (idx < len, NULL);
+
+  return GST_BUFFER_MEM_PTR (buffer, idx);
+}
+
 /**
  * gst_buffer_get_memory_range:
  * @buffer: a #GstBuffer.

gst/gstbuffer.h

@@ -269,6 +269,7 @@ GstBuffer * gst_buffer_new_wrapped         (gpointer data, gsize size);
 guint       gst_buffer_n_memory             (GstBuffer *buffer);
 void        gst_buffer_insert_memory        (GstBuffer *buffer, gint idx, GstMemory *mem);
 void        gst_buffer_replace_memory_range (GstBuffer *buffer, guint idx, gint length, GstMemory *mem);
+GstMemory * gst_buffer_peek_memory          (GstBuffer *buffer, guint idx);
 GstMemory * gst_buffer_get_memory_range     (GstBuffer *buffer, guint idx, gint length);
 void        gst_buffer_remove_memory_range  (GstBuffer *buffer, guint idx, gint length);
 

win32/common/libgstreamer.def

@@ -120,6 +120,7 @@ EXPORTS
 	gst_buffer_new_allocate
 	gst_buffer_new_wrapped
 	gst_buffer_new_wrapped_full
+	gst_buffer_peek_memory
 	gst_buffer_pool_acquire_buffer
 	gst_buffer_pool_acquire_flags_get_type
 	gst_buffer_pool_config_add_option