res_pjsip/rtp: No joint capabilities between streams.

When a conference contained a mixture of audio/video and audio-only
users, a NOTICE message would pop up stating there are no joint
capabilities between streams. This happens because streams can never be
removed, but they can be in a REMOVED state. If we have the scenario
where user A joins with audio/video, user B joins with audio-only, and
user C joins with audio/video, then user A leaves, the message would
be triggered. That removed stream is still in the SDP, but Asterisk
would pass it through, causing it to be seen as a ulaw stream. A check
has been added for removed streams, setting their status to REMOVED when
handling negotiated SDPs.

Also addressed an issue where user A joins, then user B joins but does
not receive video until much later. Full frames were not being sent,
causing some PLI from the browser. Because the video was flowing in one
direction, the browser sets the SSRC to 1, but Asterisk was dropping the
PLI because of that. Added a check to see if the SSRC is 1 or not, which
sends full frames and allows video to flow between user A and user B.
This should only happen when dealing with PSFB or FUR, and in the case
of PSFB, only for PLI.

ASTERISK-27398

Change-Id: I26e7c6f101bc119549eeca406b5bcd25ad8ebc5e

res/res_pjsip_session.c

@@ -930,10 +930,18 @@ static int handle_negotiated_sdp(struct ast_sip_session *session, const pjmedia_
 		session_media = AST_VECTOR_GET(&session->pending_media_state->sessions, i);
 		stream = ast_stream_topology_get_stream(session->pending_media_state->topology, i);
 
-		/* The stream state will have already been set to removed when either we
+		/* Make sure that this stream is in the correct state. If we need to change
-		 * negotiate the incoming SDP stream or when we produce our own local SDP.
+		 * the state to REMOVED, then our work here is done, so go ahead and move on
-		 * This can occur if an internal thing has requested it to be removed, or if
+		 * to the next stream.
-		 * we remove it as a result of the stream limit being reached.
+		 */
+		if (!remote->media[i]->desc.port) {
+			ast_stream_set_state(stream, AST_STREAM_STATE_REMOVED);
+			continue;
+		}
+
+		/* If the stream state is REMOVED, nothing needs to be done, so move on to the
+		 * next stream. This can occur if an internal thing has requested it to be
+		 * removed, or if we remove it as a result of the stream limit being reached.
 		 */
 		if (ast_stream_get_state(stream) == AST_STREAM_STATE_REMOVED) {
 			/*

res/res_rtp_asterisk.c

@@ -5802,7 +5802,17 @@ static struct ast_frame *ast_rtcp_interpret(struct ast_rtp_instance *instance, s
 		}
 
 		if (ssrc_valid && rtp->themssrc_valid) {
-			if (ssrc != rtp->themssrc && use_packet_source) {
+			/*
+			 * If the SSRC is 1, we still need to handle RTCP since this could be a
+			 * special case. For example, if we have a unidirectional video stream, the
+			 * SSRC may be set to 1 by the browser (in the case of chromium), and requests
+			 * will still need to be processed so that video can flow as expected. This
+			 * should only be done for PLI and FUR, since there is not a way to get the
+			 * appropriate rtp instance when the SSRC is 1.
+			 */
+			int exception = (ssrc == 1 && !((pt == RTCP_PT_PSFB && rc == AST_RTP_RTCP_FMT_PLI) || pt == RTCP_PT_FUR));
+			if ((ssrc != rtp->themssrc && use_packet_source && ssrc != 1)
+					|| exception) {
 				/*
 				 * Skip over this RTCP record as it does not contain the
 				 * correct SSRC.  We should not act upon RTCP records