From 39d6e40abd27c9a1f000c67906820c5e2ea89628 Mon Sep 17 00:00:00 2001
From: Sebastian Jaeckel <wose@zuendmasse.de>
Date: Tue, 16 May 2023 15:44:32 +0200
Subject: [PATCH] rtp-sap,AES67: reorder sdp records to be compatible with
 Dante/AES67 devices

A software called `Dante Controller` is needed to configure Dante
devices (which also support AES67). This software is picky about the
order in which SDP records are received and parsed.

Changing the order or adding new records in between leads to faulty
display of our stream within `Dante Controller` (missing channel display
etc.) and the user is then unable to connect any Dante device to the
AES67 stream.
---
 src/modules/module-rtp-sap.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/modules/module-rtp-sap.c b/src/modules/module-rtp-sap.c
index 70db42e55..ac5d731ae 100644
--- a/src/modules/module-rtp-sap.c
+++ b/src/modules/module-rtp-sap.c
@@ -520,35 +520,33 @@ static int send_sap(struct impl *impl, struct session *sess, bool bye)
 		snprintf(dst_ttl, sizeof(dst_ttl), "/%d", sdp->ttl);
 
 	spa_strbuf_init(&buf, buffer, sizeof(buffer));
+	/* Don't add any sdp records in between this definition or change the order
+	   it will break compatibility with Dante/AES67 devices. Add new records to
+	   the end. */
 	spa_strbuf_append(&buf,
 			"v=0\n"
 			"o=%s %u 0 IN %s %s\n"
 			"s=%s\n"
 			"c=IN %s %s%s\n"
 			"t=%u 0\n"
-			"a=recvonly\n"
-			"a=tool:PipeWire %s\n"
-			"a=type:broadcast\n",
+			"m=%s %u RTP/AVP %i\n",
 			user_name, sdp->ntp, src_ip4 ? "IP4" : "IP6", src_addr,
 			sdp->session_name,
 			dst_ip4 ? "IP4" : "IP6", dst_addr, dst_ttl,
 			sdp->ntp,
-			pw_get_library_version());
-	spa_strbuf_append(&buf,
-			"m=%s %u RTP/AVP %i\n",
-			sdp->media_type,
-			sdp->dst_port, sdp->payload);
+			sdp->media_type, sdp->dst_port, sdp->payload);
 
 	if (sdp->channels) {
-		spa_strbuf_append(&buf,
-			"a=rtpmap:%i %s/%u/%u\n",
-				sdp->payload, sdp->mime_type,
-				sdp->rate, sdp->channels);
 		if (sdp->channelmap[0] != 0) {
 			spa_strbuf_append(&buf,
 				"i=%d channels: %s\n", sdp->channels,
 				sdp->channelmap);
 		}
+		spa_strbuf_append(&buf,
+			"a=recvonly\n"
+			"a=rtpmap:%i %s/%u/%u\n",
+				sdp->payload, sdp->mime_type,
+				sdp->rate, sdp->channels);
 	} else {
 		spa_strbuf_append(&buf,
 			"a=rtpmap:%i %s/%u\n",
@@ -569,6 +567,11 @@ static int send_sap(struct impl *impl, struct session *sess, bool bye)
 		spa_strbuf_append(&buf, "a=mediaclk:sender\n");
 	}
 
+	spa_strbuf_append(&buf,
+		"a=tool:PipeWire %s\n"
+		"a=type:broadcast\n",
+		pw_get_library_version());
+
 	pw_log_debug("sending SAP for %u %s", sess->node->id, buffer);
 
 	iov[3].iov_base = buffer;