backport fix from trunk for bug #6934, ensuring that RTP mark bit is changed when SSRC changes

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@26773 65c4cc65-6c06-0410-ace0-fbb531ad65f3

rtp.c

@@ -90,6 +90,7 @@ struct ast_rtp {
 	unsigned char rawdata[8192 + AST_FRIENDLY_OFFSET];
 	/*! Synchronization source, RFC 3550, page 10. */
 	unsigned int ssrc;
+	unsigned int rxssrc;
 	unsigned int lastts;
 	unsigned int lastdigitts;
 	unsigned int lastrxts;
@@ -436,6 +437,7 @@ struct ast_frame *ast_rtp_read(struct ast_rtp *rtp)
 	int ext;
 	int x;
 	char iabuf[INET_ADDRSTRLEN];
+	unsigned int ssrc;
 	unsigned int timestamp;
 	unsigned int *rtpheader;
 	static struct ast_frame *f, null_frame = { AST_FRAME_NULL, };
@@ -492,6 +494,14 @@ struct ast_frame *ast_rtp_read(struct ast_rtp *rtp)
 	ext = seqno & (1 << 28);
 	seqno &= 0xffff;
 	timestamp = ntohl(rtpheader[1]);
+	ssrc = ntohl(rtpheader[2]);
+	
+	if (!mark && rtp->rxssrc && rtp->rxssrc != ssrc) {
+		ast_log(LOG_WARNING, "Forcing Marker bit, because SSRC has changed\n");
+		mark = 1;
+	}
+
+	rtp->rxssrc = ssrc;
 	
 	if (padding) {
 		/* Remove padding bytes */