MT#55283 new "mix" flag

Change-Id: I4d1dfa2a38533707e9c0f080377c880fc3b678a5

daemon/call.c

@@ -4434,9 +4434,25 @@ static int monologue_subscribe_request1(struct call_media *src_media, struct cal
 	if (ms)
 		dst_media = ms->media;
 	if (!dst_media) {
-		// new media needed
-		dst_media = call_get_media(dst_ml, &src_media->type, src_media->type_id,
-				NULL, false, dst_ml->medias->len + 1, mid_tracker_dst);
+		if (flags->mix) {
+			// find existing matching media
+			for (unsigned int i = 0; i < dst_ml->medias->len; i++) {
+				struct call_media *m = dst_ml->medias->pdata[i];
+				if (!m)
+					continue;
+				if (m->type_id != src_media->type_id)
+					continue;
+				if (str_cmp_str(&m->type, &src_media->type))
+					continue;
+				dst_media = m;
+				break;
+			}
+		}
+		if (!dst_media) {
+			// new media needed
+			dst_media = call_get_media(dst_ml, &src_media->type, src_media->type_id,
+					NULL, false, dst_ml->medias->len + 1, mid_tracker_dst);
+		}
 	}
 
 	/* subscribe dst_ml (subscriber) to src_ml, don't forget to carry the egress flag, if required */

daemon/call_interfaces.c

@@ -1218,6 +1218,10 @@ void call_ng_flags_flags(str *s, unsigned int idx, helper_arg arg) {
 		case CSH_LOOKUP("rtcp mirror"):
 			out->rtcp_mirror = true;
 			break;
+		case CSH_LOOKUP("mix"):
+		case CSH_LOOKUP("mixed"):
+			out->mix = true;
+			break;
 		case CSH_LOOKUP("NAT-wait"):
 		case CSH_LOOKUP("nat-wait"):
 		case CSH_LOOKUP("NAT wait"):

docs/ng_control_protocol.md

@@ -1168,6 +1168,19 @@ Spaces in each string may be replaced by hyphens.
 	this opens a security hole and potentially allows RTP streams to be hijacked, either partly or
 	in whole.
 
+* `mix`
+
+    For a subscribe request to subscribe to multiple source medias (e.g.
+    subscribe to the audio of both parties to a regular call), instead of
+    producing one output media per source media (e.g. two output audio media),
+    produce one output media for each type of source media (e.g. just one
+    output audio media). All affected RTP flows will then be sent as part of
+    the same output media.
+
+    Not that this doesn't enable actual audio mixing. The `audio player`
+    feature can be used to produce a single mixed output audio stream which
+    combines all audio input into one.
+
 * `NAT-wait`
 
 	Prevents forwarding media packets to the respective endpoint

include/call_interfaces.h

@@ -223,6 +223,7 @@ RTPE_NG_FLAGS_STR_CASE_HT_PARAMS
 	             bundle_strict:1,
 		     ice_reject:1,
 		     rtcp_mirror:1,
+		     mix:1,
 		     trickle_ice:1,
 	             no_rtcp_attr:1,
 	             no_tls_id:1,