Add @file doxy.

Originally committed as revision 24364 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vsrc_buffer.c

@@ -1,5 +1,4 @@
 /*
- * Memory buffer source filter
  * Copyright (c) 2008 Vitor Sessak
  *
  * This file is part of FFmpeg.
@@ -19,6 +18,11 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+/**
+ * @file
+ * memory buffer source filter
+ */
+
 #include "avfilter.h"
 #include "vsrc_buffer.h"