diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
index b1f2a84584..6375a3e60f 100644
--- a/libavformat/rtsp.c
+++ b/libavformat/rtsp.c
@@ -563,6 +563,10 @@ static int sdp_parse(AVFormatContext *s, const char *content)
 {
     const char *p;
     int letter;
+    /* Some SDP lines, particularly for Realmedia or ASF RTSP streams, contain long SDP
+     * lines containing complete ASF Headers (several kB) or arrays of MDPR (RM stream
+     * descriptor) headers plus "rulebooks" describing their properties. Therefore, the
+     * SDP line buffer is large. */
     char buf[8192], *q;
     SDPParseState sdp_parse_state, *s1 = &sdp_parse_state;