vsrc_buffer.h: add file doxy

Signed-off-by: Stefano Sabatini <stefano.sabatini-lala@poste.it>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavfilter/vsrc_buffer.h

@@ -22,6 +22,11 @@
 #ifndef AVFILTER_VSRC_BUFFER_H
 #define AVFILTER_VSRC_BUFFER_H
 
+/**
+ * @file
+ * memory buffer source API for video
+ */
+
 #include "libavcodec/avcodec.h" /* AVFrame */
 #include "avfilter.h"