commit 5f94aa2c013e5a09ab17cec76b104879d059af2a
author Steve Anton <steveanton@webrtc.org> Thu Feb 01 18:58:30 2018
committer Commit Bot <commit-bot@chromium.org> Thu Feb 01 19:58:31 2018
tree b76c50fb668da697e527a7f70c2063e2b2bfd20e
parent edab3011fa79803ed4e93836d924d266cd4df013

Correct MSID behavior with Unified Plan

This changes the behavior of CreateOffer/CreateAnswer when Unified
Plan is enabled to be in line with that specified in JSEP.

In particular, MSID information is now only included if the
RtpTransceiver is not stopped and either is sending or has ever
sent.

Bug: webrtc:7600
Change-Id: I6400f0583525c7776331eeb0e1bb53973bc02dfb
Reviewed-on: https://webrtc-review.googlesource.com/46400
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21857}

pc/peerconnection.cc

diff --git a/pc/peerconnection.cc b/pc/peerconnection.cc
index 0596869..c361468 100644
--- a/pc/peerconnection.cc
+++ b/pc/peerconnection.cc
@@ -2150,9 +2150,8 @@
         transceiver->Stop();
       }
       if (!content->rejected && !media_desc->streams().empty()) {
-        const auto& stream = content->media_description()->streams()[0];
         transceiver->internal()->receiver_internal()->SetupMediaChannel(
-            stream.first_ssrc());
+            media_desc->streams()[0].first_ssrc());
       }
     }
     for (auto event : track_events) {
@@ -2410,8 +2409,13 @@
     if (!transceiver) {
       auto sender =
           CreateSender(media_desc->type(), nullptr, {rtc::CreateRandomUuid()});
-      auto receiver =
-          CreateReceiver(media_desc->type(), media_desc->streams()[0].id);
+      std::string receiver_id;
+      if (!media_desc->streams().empty()) {
+        receiver_id = media_desc->streams()[0].id;
+      } else {
+        receiver_id = rtc::CreateRandomUuid();
+      }
+      auto receiver = CreateReceiver(media_desc->type(), receiver_id);
       transceiver = CreateAndAddTransceiver(sender, receiver);
       transceiver->internal()->set_direction(
           RtpTransceiverDirection::kRecvOnly);
@@ -3304,13 +3308,22 @@
   cricket::MediaDescriptionOptions media_description_options(
       transceiver->internal()->media_type(), mid, transceiver->direction(),
       transceiver->stopped());
-  cricket::SenderOptions sender_options;
-  sender_options.track_id = transceiver->sender()->id();
-  sender_options.stream_ids = transceiver->sender()->stream_ids();
-  // TODO(bugs.webrtc.org/7600): Set num_sim_layers to the number of encodings
-  // set in the RTP parameters when the transceiver was added.
-  sender_options.num_sim_layers = 1;
-  media_description_options.sender_options.push_back(sender_options);
+  // This behavior is specified in JSEP. The gist is that:
+  // 1. The MSID is included if the RtpTransceiver's direction is sendonly or
+  //    sendrecv.
+  // 2. If the MSID is included, then it must be included in any subsequent
+  //    offer/answer exactly the same until the RtpTransceiver is stopped.
+  if (!transceiver->stopped() &&
+      (RtpTransceiverDirectionHasSend(transceiver->direction()) ||
+       transceiver->internal()->has_ever_been_used_to_send())) {
+    cricket::SenderOptions sender_options;
+    sender_options.track_id = transceiver->sender()->id();
+    sender_options.stream_ids = transceiver->sender()->stream_ids();
+    // TODO(bugs.webrtc.org/7600): Set num_sim_layers to the number of encodings
+    // set in the RTP parameters when the transceiver was added.
+    sender_options.num_sim_layers = 1;
+    media_description_options.sender_options.push_back(sender_options);
+  }
   return media_description_options;
 }