Reland "Don't create channel_manager++ when media_engine is not set"

This reverts commit c6c02efb56b24df04ed9ab61252c14c7bddcca93.

Reason for revert: Test now passes (and channel manager is gone)

Original change's description:
> Revert "Don't create channel_manager when media_engine is not set"
>
> This reverts commit c48ad732d6eb69f14dd6d44f801d62997cef2c2f.
>
> Reason for revert: breaks downstream project
>
> Original change's description:
> > Don't create channel_manager when media_engine is not set
> >
> > Also remove a bunch of functions in ChannelManager that were just
> > forwarding to MediaEngineInterface.
> >
> > Bug: webrtc:13931
> > Change-Id: Ia38591fd22c665cace16d032f5c1e384e413cded
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261304
> > Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
> > Reviewed-by: Henrik Boström <hbos@webrtc.org>
> > Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> > Cr-Commit-Position: refs/heads/main@{#36801}
>
> Bug: webrtc:13931
> Change-Id: I1e260a2489547bd9483b50e043c28d2805b0fa5a
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261660
> Commit-Queue: Artem Titov <titovartem@webrtc.org>
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Owners-Override: Artem Titov <titovartem@webrtc.org>
> Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#36811}

Bug: webrtc:13931
Change-Id: I7b5b45b46095c18d489b6a9fe4c625971d6b3da6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261661
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36976}
diff --git a/pc/BUILD.gn b/pc/BUILD.gn
index 24ea680..d4acaed 100644
--- a/pc/BUILD.gn
+++ b/pc/BUILD.gn
@@ -329,6 +329,7 @@
     "../rtc_base:checks",
     "../rtc_base:logging",
     "../rtc_base:stringutils",
+    "../rtc_base/memory:always_valid_pointer",
     "../rtc_base/third_party/base64",
   ]
   absl_deps = [
diff --git a/pc/data_channel_integrationtest.cc b/pc/data_channel_integrationtest.cc
index d184a81..faec76d 100644
--- a/pc/data_channel_integrationtest.cc
+++ b/pc/data_channel_integrationtest.cc
@@ -58,10 +58,24 @@
 
 class DataChannelIntegrationTest
     : public PeerConnectionIntegrationBaseTest,
-      public ::testing::WithParamInterface<SdpSemantics> {
+      public ::testing::WithParamInterface<std::tuple<SdpSemantics, bool>> {
  protected:
   DataChannelIntegrationTest()
-      : PeerConnectionIntegrationBaseTest(GetParam()) {}
+      : PeerConnectionIntegrationBaseTest(std::get<0>(GetParam())),
+        allow_media_(std::get<1>(GetParam())) {}
+  bool allow_media() { return allow_media_; }
+
+  bool CreatePeerConnectionWrappers() {
+    if (allow_media_) {
+      return PeerConnectionIntegrationBaseTest::CreatePeerConnectionWrappers();
+    }
+    return PeerConnectionIntegrationBaseTest::
+        CreatePeerConnectionWrappersWithoutMediaEngine();
+  }
+
+ private:
+  // True if media is allowed to be added
+  const bool allow_media_;
 };
 
 // Fake clock must be set before threads are started to prevent race on
@@ -173,14 +187,18 @@
   // Expect that data channel created on caller side will show up for callee as
   // well.
   caller()->CreateDataChannel();
-  caller()->AddAudioVideoTracks();
-  callee()->AddAudioVideoTracks();
+  if (allow_media()) {
+    caller()->AddAudioVideoTracks();
+    callee()->AddAudioVideoTracks();
+  }
   caller()->CreateAndSetAndSignalOffer();
   ASSERT_TRUE_WAIT(SignalingStateStable(), kDefaultTimeout);
-  // Ensure the existence of the SCTP data channel didn't impede audio/video.
-  MediaExpectations media_expectations;
-  media_expectations.ExpectBidirectionalAudioAndVideo();
-  ASSERT_TRUE(ExpectNewFrames(media_expectations));
+  if (allow_media()) {
+    // Ensure the existence of the SCTP data channel didn't impede audio/video.
+    MediaExpectations media_expectations;
+    media_expectations.ExpectBidirectionalAudioAndVideo();
+    ASSERT_TRUE(ExpectNewFrames(media_expectations));
+  }
   // Caller data channel should already exist (it created one). Callee data
   // channel may not exist yet, since negotiation happens in-band, not in SDP.
   ASSERT_NE(nullptr, caller()->data_channel());
@@ -202,7 +220,7 @@
 // data channel only, and sends messages of various sizes.
 TEST_P(DataChannelIntegrationTest,
        EndToEndCallWithSctpDataChannelVariousSizes) {
-  ASSERT_TRUE(CreatePeerConnectionWrappersWithoutMediaEngine());
+  ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   // Expect that data channel created on caller side will show up for callee as
   // well.
@@ -241,7 +259,7 @@
 // data channel only, and sends empty messages
 TEST_P(DataChannelIntegrationTest,
        EndToEndCallWithSctpDataChannelEmptyMessages) {
-  ASSERT_TRUE(CreatePeerConnectionWrappersWithoutMediaEngine());
+  ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   // Expect that data channel created on caller side will show up for callee as
   // well.
@@ -291,7 +309,7 @@
   // this test does not use TURN.
   const size_t kLowestSafePayloadSizeLimit = 1225;
 
-  ASSERT_TRUE(CreatePeerConnectionWrappersWithoutMediaEngine());
+  ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   // Expect that data channel created on caller side will show up for callee as
   // well.
@@ -328,7 +346,7 @@
   // The size of the smallest message that fails to be delivered.
   const size_t kMessageSizeThatIsNotDelivered = 1157;
 
-  ASSERT_TRUE(CreatePeerConnectionWrappersWithoutMediaEngine());
+  ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   caller()->CreateDataChannel();
   caller()->CreateAndSetAndSignalOffer();
@@ -369,8 +387,10 @@
   ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   caller()->CreateDataChannel();
-  caller()->AddAudioVideoTracks();
-  callee()->AddAudioVideoTracks();
+  if (allow_media()) {
+    caller()->AddAudioVideoTracks();
+    callee()->AddAudioVideoTracks();
+  }
   caller()->CreateAndSetAndSignalOffer();
   ASSERT_TRUE_WAIT(SignalingStateStable(), kDefaultTimeout);
   ASSERT_NE(nullptr, caller()->data_channel());
@@ -406,8 +426,10 @@
   init.id = 53;
   init.maxRetransmits = 52;
   caller()->CreateDataChannel("data-channel", &init);
-  caller()->AddAudioVideoTracks();
-  callee()->AddAudioVideoTracks();
+  if (allow_media()) {
+    caller()->AddAudioVideoTracks();
+    callee()->AddAudioVideoTracks();
+  }
   caller()->CreateAndSetAndSignalOffer();
   ASSERT_TRUE_WAIT(SignalingStateStable(), kDefaultTimeout);
   ASSERT_TRUE_WAIT(callee()->data_channel() != nullptr, kDefaultTimeout);
@@ -429,7 +451,7 @@
   virtual_socket_server()->set_delay_stddev(5);
   virtual_socket_server()->UpdateDelayDistribution();
   // Normal procedure, but with unordered data channel config.
-  ASSERT_TRUE(CreatePeerConnectionWrappersWithoutMediaEngine());
+  ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   webrtc::DataChannelInit init;
   init.ordered = false;
@@ -633,6 +655,10 @@
 // This test sets up a call between two parties with audio, and video. When
 // audio and video are setup and flowing, an SCTP data channel is negotiated.
 TEST_P(DataChannelIntegrationTest, AddSctpDataChannelInSubsequentOffer) {
+  // This test can't be performed without media.
+  if (!allow_media()) {
+    return;
+  }
   ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   // Do initial offer/answer with audio/video.
@@ -665,6 +691,10 @@
 // Effectively the inverse of the test above. This was broken in M57; see
 // https://crbug.com/711243
 TEST_P(DataChannelIntegrationTest, SctpDataChannelToAudioVideoUpgrade) {
+  // This test can't be performed without media.
+  if (!allow_media()) {
+    return;
+  }
   ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
   // Do initial offer/answer with just data channel.
@@ -724,6 +754,10 @@
 // Test that after closing PeerConnections, they stop sending any packets
 // (ICE, DTLS, RTP...).
 TEST_P(DataChannelIntegrationTest, ClosingConnectionStopsPacketFlow) {
+  // This test can't be performed without media.
+  if (!allow_media()) {
+    return;
+  }
   // Set up audio/video/data, wait for some frames to be received.
   ASSERT_TRUE(CreatePeerConnectionWrappers());
   ConnectFakeSignaling();
@@ -1055,8 +1089,9 @@
 
 INSTANTIATE_TEST_SUITE_P(DataChannelIntegrationTest,
                          DataChannelIntegrationTest,
-                         Values(SdpSemantics::kPlanB_DEPRECATED,
-                                SdpSemantics::kUnifiedPlan));
+                         Combine(Values(SdpSemantics::kPlanB_DEPRECATED,
+                                        SdpSemantics::kUnifiedPlan),
+                                 testing::Bool()));
 
 TEST_F(DataChannelIntegrationTestUnifiedPlan,
        EndToEndCallWithBundledSctpDataChannel) {
diff --git a/pc/media_session.cc b/pc/media_session.cc
index ec4b6a2..3f7dbb5 100644
--- a/pc/media_session.cc
+++ b/pc/media_session.cc
@@ -1566,9 +1566,7 @@
     const TransportDescriptionFactory* transport_desc_factory,
     rtc::UniqueRandomIdGenerator* ssrc_generator)
     : ssrc_generator_(ssrc_generator),
-      transport_desc_factory_(transport_desc_factory) {
-  RTC_DCHECK(ssrc_generator_);
-}
+      transport_desc_factory_(transport_desc_factory) {}
 
 MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
     cricket::MediaEngineInterface* media_engine,
@@ -2366,7 +2364,7 @@
   if (!CreateMediaContentOffer(
           media_description_options, session_options, filtered_codecs,
           sdes_policy, GetCryptos(current_content), crypto_suites,
-          audio_rtp_extensions, ssrc_generator_, current_streams, audio.get(),
+          audio_rtp_extensions, ssrc_generator(), current_streams, audio.get(),
           transport_desc_factory_->trials())) {
     return false;
   }
@@ -2478,7 +2476,7 @@
   if (!CreateMediaContentOffer(
           media_description_options, session_options, filtered_codecs,
           sdes_policy, GetCryptos(current_content), crypto_suites,
-          video_rtp_extensions, ssrc_generator_, current_streams, video.get(),
+          video_rtp_extensions, ssrc_generator(), current_streams, video.get(),
           transport_desc_factory_->trials())) {
     return false;
   }
@@ -2531,8 +2529,8 @@
 
   if (!CreateContentOffer(media_description_options, session_options,
                           sdes_policy, GetCryptos(current_content),
-                          crypto_suites, RtpHeaderExtensions(), ssrc_generator_,
-                          current_streams, data.get())) {
+                          crypto_suites, RtpHeaderExtensions(),
+                          ssrc_generator(), current_streams, data.get())) {
     return false;
   }
 
@@ -2673,7 +2671,7 @@
       audio_transport->secure() ? cricket::SEC_DISABLED : secure();
   if (!SetCodecsInAnswer(offer_audio_description, filtered_codecs,
                          media_description_options, session_options,
-                         ssrc_generator_, current_streams, audio_answer.get(),
+                         ssrc_generator(), current_streams, audio_answer.get(),
                          transport_desc_factory_->trials())) {
     return false;
   }
@@ -2681,7 +2679,7 @@
           offer_audio_description, media_description_options, session_options,
           sdes_policy, GetCryptos(current_content),
           filtered_rtp_header_extensions(default_audio_rtp_header_extensions),
-          ssrc_generator_, enable_encrypted_rtp_header_extensions_,
+          ssrc_generator(), enable_encrypted_rtp_header_extensions_,
           current_streams, bundle_enabled, audio_answer.get())) {
     return false;  // Fails the session setup.
   }
@@ -2809,7 +2807,7 @@
       video_transport->secure() ? cricket::SEC_DISABLED : secure();
   if (!SetCodecsInAnswer(offer_video_description, filtered_codecs,
                          media_description_options, session_options,
-                         ssrc_generator_, current_streams, video_answer.get(),
+                         ssrc_generator(), current_streams, video_answer.get(),
                          transport_desc_factory_->trials())) {
     return false;
   }
@@ -2817,7 +2815,7 @@
           offer_video_description, media_description_options, session_options,
           sdes_policy, GetCryptos(current_content),
           filtered_rtp_header_extensions(default_video_rtp_header_extensions),
-          ssrc_generator_, enable_encrypted_rtp_header_extensions_,
+          ssrc_generator(), enable_encrypted_rtp_header_extensions_,
           current_streams, bundle_enabled, video_answer.get())) {
     return false;  // Failed the session setup.
   }
@@ -2890,7 +2888,7 @@
     if (!CreateMediaContentAnswer(
             offer_data_description, media_description_options, session_options,
             sdes_policy, GetCryptos(current_content), RtpHeaderExtensions(),
-            ssrc_generator_, enable_encrypted_rtp_header_extensions_,
+            ssrc_generator(), enable_encrypted_rtp_header_extensions_,
             current_streams, bundle_enabled, data_answer.get())) {
       return false;  // Fails the session setup.
     }
diff --git a/pc/media_session.h b/pc/media_session.h
index ef2893d..3711110 100644
--- a/pc/media_session.h
+++ b/pc/media_session.h
@@ -34,6 +34,7 @@
 #include "pc/media_protocol_names.h"
 #include "pc/session_description.h"
 #include "pc/simulcast_description.h"
+#include "rtc_base/memory/always_valid_pointer.h"
 #include "rtc_base/unique_id_generator.h"
 
 namespace webrtc {
@@ -331,6 +332,10 @@
 
   void ComputeVideoCodecsIntersectionAndUnion();
 
+  rtc::UniqueRandomIdGenerator* ssrc_generator() const {
+    return ssrc_generator_.get();
+  }
+
   bool is_unified_plan_ = false;
   AudioCodecs audio_send_codecs_;
   AudioCodecs audio_recv_codecs_;
@@ -344,8 +349,9 @@
   VideoCodecs video_sendrecv_codecs_;
   // Union of send and recv.
   VideoCodecs all_video_codecs_;
-  // This object is not owned by the channel so it must outlive it.
-  rtc::UniqueRandomIdGenerator* const ssrc_generator_;
+  // This object may or may not be owned by this class.
+  webrtc::AlwaysValidPointer<rtc::UniqueRandomIdGenerator> const
+      ssrc_generator_;
   bool enable_encrypted_rtp_header_extensions_ = false;
   // TODO(zhihuang): Rename secure_ to sdec_policy_; rename the related getter
   // and setter.
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index c3b29d0..c277ac0 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -1172,8 +1172,10 @@
     const {
   RTC_DCHECK_RUN_ON(signaling_thread());
   std::vector<rtc::scoped_refptr<RtpSenderInterface>> ret;
-  for (const auto& sender : rtp_manager()->GetSendersInternal()) {
-    ret.push_back(sender);
+  if (ConfiguredForMedia()) {
+    for (const auto& sender : rtp_manager()->GetSendersInternal()) {
+      ret.push_back(sender);
+    }
   }
   return ret;
 }
@@ -1182,8 +1184,10 @@
 PeerConnection::GetReceivers() const {
   RTC_DCHECK_RUN_ON(signaling_thread());
   std::vector<rtc::scoped_refptr<RtpReceiverInterface>> ret;
-  for (const auto& receiver : rtp_manager()->GetReceiversInternal()) {
-    ret.push_back(receiver);
+  if (ConfiguredForMedia()) {
+    for (const auto& receiver : rtp_manager()->GetReceiversInternal()) {
+      ret.push_back(receiver);
+    }
   }
   return ret;
 }
@@ -1194,8 +1198,10 @@
   RTC_CHECK(IsUnifiedPlan())
       << "GetTransceivers is only supported with Unified Plan SdpSemantics.";
   std::vector<rtc::scoped_refptr<RtpTransceiverInterface>> all_transceivers;
-  for (const auto& transceiver : rtp_manager()->transceivers()->List()) {
-    all_transceivers.push_back(transceiver);
+  if (ConfiguredForMedia()) {
+    for (const auto& transceiver : rtp_manager()->transceivers()->List()) {
+      all_transceivers.push_back(transceiver);
+    }
   }
   return all_transceivers;
 }
@@ -1814,12 +1820,13 @@
 
   NoteUsageEvent(UsageEvent::CLOSE_CALLED);
 
-  for (const auto& transceiver : rtp_manager()->transceivers()->List()) {
-    transceiver->internal()->SetPeerConnectionClosed();
-    if (!transceiver->stopped())
-      transceiver->StopInternal();
+  if (ConfiguredForMedia()) {
+    for (const auto& transceiver : rtp_manager()->transceivers()->List()) {
+      transceiver->internal()->SetPeerConnectionClosed();
+      if (!transceiver->stopped())
+        transceiver->StopInternal();
+    }
   }
-
   // Ensure that all asynchronous stats requests are completed before destroying
   // the transport controller below.
   if (stats_collector_) {
@@ -1836,7 +1843,9 @@
   // WebRTC session description factory, the session description factory would
   // call the transport controller.
   sdp_handler_->ResetSessionDescFactory();
-  rtp_manager_->Close();
+  if (ConfiguredForMedia()) {
+    rtp_manager_->Close();
+  }
 
   network_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
     // Data channels will already have been unset via the DestroyAllChannels()
@@ -2727,12 +2736,15 @@
   rtc::Thread::ScopedDisallowBlockingCalls no_blocking_calls;
   std::map<std::string, std::set<cricket::MediaType>>
       media_types_by_transport_name;
-  for (const auto& transceiver : rtp_manager()->transceivers()->UnsafeList()) {
-    if (transceiver->internal()->channel()) {
-      std::string transport_name(
-          transceiver->internal()->channel()->transport_name());
-      media_types_by_transport_name[transport_name].insert(
-          transceiver->media_type());
+  if (ConfiguredForMedia()) {
+    for (const auto& transceiver :
+         rtp_manager()->transceivers()->UnsafeList()) {
+      if (transceiver->internal()->channel()) {
+        std::string transport_name(
+            transceiver->internal()->channel()->transport_name());
+        media_types_by_transport_name[transport_name].insert(
+            transceiver->media_type());
+      }
     }
   }
 
@@ -2880,10 +2892,13 @@
     DataChannelTransportInterface* data_channel_transport) {
   RTC_DCHECK_RUN_ON(network_thread());
   bool ret = true;
-  for (const auto& transceiver : rtp_manager()->transceivers()->UnsafeList()) {
-    cricket::ChannelInterface* channel = transceiver->internal()->channel();
-    if (channel && channel->mid() == mid) {
-      ret = channel->SetRtpTransport(rtp_transport);
+  if (ConfiguredForMedia()) {
+    for (const auto& transceiver :
+         rtp_manager()->transceivers()->UnsafeList()) {
+      cricket::ChannelInterface* channel = transceiver->internal()->channel();
+      if (channel && channel->mid() == mid) {
+        ret = channel->SetRtpTransport(rtp_transport);
+      }
     }
   }
 
diff --git a/pc/peer_connection.h b/pc/peer_connection.h
index 51dbea8..7dd6446 100644
--- a/pc/peer_connection.h
+++ b/pc/peer_connection.h
@@ -273,6 +273,9 @@
       rtc::scoped_refptr<RtpTransceiverProxyWithInternal<RtpTransceiver>>>
   GetTransceiversInternal() const override {
     RTC_DCHECK_RUN_ON(signaling_thread());
+    if (!ConfiguredForMedia()) {
+      return {};
+    }
     return rtp_manager()->transceivers()->List();
   }
 
diff --git a/pc/rtp_transceiver.cc b/pc/rtp_transceiver.cc
index 4a0fce7..5ca662c 100644
--- a/pc/rtp_transceiver.cc
+++ b/pc/rtp_transceiver.cc
@@ -23,6 +23,7 @@
 #include "api/sequence_checker.h"
 #include "media/base/codec.h"
 #include "media/base/media_constants.h"
+#include "media/base/media_engine.h"
 #include "pc/channel.h"
 #include "pc/rtp_media_utils.h"
 #include "pc/session_description.h"
@@ -602,7 +603,6 @@
 RTCError RtpTransceiver::SetCodecPreferences(
     rtc::ArrayView<RtpCodecCapability> codec_capabilities) {
   RTC_DCHECK(unified_plan_);
-
   // 3. If codecs is an empty list, set transceiver's [[PreferredCodecs]] slot
   // to codecs and abort these steps.
   if (codec_capabilities.empty()) {
diff --git a/pc/sdp_offer_answer.cc b/pc/sdp_offer_answer.cc
index f84d37c..f163851 100644
--- a/pc/sdp_offer_answer.cc
+++ b/pc/sdp_offer_answer.cc
@@ -1549,56 +1549,60 @@
                         << ")";
       return error;
     }
-    std::vector<rtc::scoped_refptr<RtpTransceiverInterface>> remove_list;
-    std::vector<rtc::scoped_refptr<MediaStreamInterface>> removed_streams;
-    for (const auto& transceiver_ext : transceivers()->List()) {
-      auto transceiver = transceiver_ext->internal();
-      if (transceiver->stopped()) {
-        continue;
-      }
-
-      // 2.2.7.1.1.(6-9): Set sender and receiver's transport slots.
-      // Note that code paths that don't set MID won't be able to use
-      // information about DTLS transports.
-      if (transceiver->mid()) {
-        auto dtls_transport = LookupDtlsTransportByMid(
-            context_->network_thread(), transport_controller_s(),
-            *transceiver->mid());
-        transceiver->sender_internal()->set_transport(dtls_transport);
-        transceiver->receiver_internal()->set_transport(dtls_transport);
-      }
-
-      const ContentInfo* content =
-          FindMediaSectionForTransceiver(transceiver, local_description());
-      if (!content) {
-        continue;
-      }
-      const MediaContentDescription* media_desc = content->media_description();
-      // 2.2.7.1.6: If description is of type "answer" or "pranswer", then run
-      // the following steps:
-      if (type == SdpType::kPrAnswer || type == SdpType::kAnswer) {
-        // 2.2.7.1.6.1: If direction is "sendonly" or "inactive", and
-        // transceiver's [[FiredDirection]] slot is either "sendrecv" or
-        // "recvonly", process the removal of a remote track for the media
-        // description, given transceiver, removeList, and muteTracks.
-        if (!RtpTransceiverDirectionHasRecv(media_desc->direction()) &&
-            (transceiver->fired_direction() &&
-             RtpTransceiverDirectionHasRecv(*transceiver->fired_direction()))) {
-          ProcessRemovalOfRemoteTrack(transceiver_ext, &remove_list,
-                                      &removed_streams);
+    if (ConfiguredForMedia()) {
+      std::vector<rtc::scoped_refptr<RtpTransceiverInterface>> remove_list;
+      std::vector<rtc::scoped_refptr<MediaStreamInterface>> removed_streams;
+      for (const auto& transceiver_ext : transceivers()->List()) {
+        auto transceiver = transceiver_ext->internal();
+        if (transceiver->stopped()) {
+          continue;
         }
-        // 2.2.7.1.6.2: Set transceiver's [[CurrentDirection]] and
-        // [[FiredDirection]] slots to direction.
-        transceiver->set_current_direction(media_desc->direction());
-        transceiver->set_fired_direction(media_desc->direction());
+
+        // 2.2.7.1.1.(6-9): Set sender and receiver's transport slots.
+        // Note that code paths that don't set MID won't be able to use
+        // information about DTLS transports.
+        if (transceiver->mid()) {
+          auto dtls_transport = LookupDtlsTransportByMid(
+              context_->network_thread(), transport_controller_s(),
+              *transceiver->mid());
+          transceiver->sender_internal()->set_transport(dtls_transport);
+          transceiver->receiver_internal()->set_transport(dtls_transport);
+        }
+
+        const ContentInfo* content =
+            FindMediaSectionForTransceiver(transceiver, local_description());
+        if (!content) {
+          continue;
+        }
+        const MediaContentDescription* media_desc =
+            content->media_description();
+        // 2.2.7.1.6: If description is of type "answer" or "pranswer", then run
+        // the following steps:
+        if (type == SdpType::kPrAnswer || type == SdpType::kAnswer) {
+          // 2.2.7.1.6.1: If direction is "sendonly" or "inactive", and
+          // transceiver's [[FiredDirection]] slot is either "sendrecv" or
+          // "recvonly", process the removal of a remote track for the media
+          // description, given transceiver, removeList, and muteTracks.
+          if (!RtpTransceiverDirectionHasRecv(media_desc->direction()) &&
+              (transceiver->fired_direction() &&
+               RtpTransceiverDirectionHasRecv(
+                   *transceiver->fired_direction()))) {
+            ProcessRemovalOfRemoteTrack(transceiver_ext, &remove_list,
+                                        &removed_streams);
+          }
+          // 2.2.7.1.6.2: Set transceiver's [[CurrentDirection]] and
+          // [[FiredDirection]] slots to direction.
+          transceiver->set_current_direction(media_desc->direction());
+          transceiver->set_fired_direction(media_desc->direction());
+        }
       }
-    }
-    auto observer = pc_->Observer();
-    for (const auto& transceiver : remove_list) {
-      observer->OnRemoveTrack(transceiver->receiver());
-    }
-    for (const auto& stream : removed_streams) {
-      observer->OnRemoveStream(stream);
+      auto observer = pc_->Observer();
+      for (const auto& transceiver : remove_list) {
+        observer->OnRemoveTrack(transceiver->receiver());
+      }
+      for (const auto& stream : removed_streams) {
+        observer->OnRemoveStream(stream);
+      }
     }
   } else {
     // Media channels will be created only when offer is set. These may use new
@@ -1642,35 +1646,39 @@
   }
 
   if (IsUnifiedPlan()) {
-    // We must use List and not ListInternal here because
-    // transceivers()->StableState() is indexed by the non-internal refptr.
-    for (const auto& transceiver_ext : transceivers()->List()) {
-      auto transceiver = transceiver_ext->internal();
-      if (transceiver->stopped()) {
-        continue;
-      }
-      const ContentInfo* content =
-          FindMediaSectionForTransceiver(transceiver, local_description());
-      if (!content) {
-        continue;
-      }
-      cricket::ChannelInterface* channel = transceiver->channel();
-      if (content->rejected || !channel || channel->local_streams().empty()) {
-        // 0 is a special value meaning "this sender has no associated send
-        // stream". Need to call this so the sender won't attempt to configure
-        // a no longer existing stream and run into DCHECKs in the lower
-        // layers.
-        transceiver->sender_internal()->SetSsrc(0);
-      } else {
-        // Get the StreamParams from the channel which could generate SSRCs.
-        const std::vector<StreamParams>& streams = channel->local_streams();
-        transceiver->sender_internal()->set_stream_ids(streams[0].stream_ids());
-        auto encodings = transceiver->sender_internal()->init_send_encodings();
-        transceiver->sender_internal()->SetSsrc(streams[0].first_ssrc());
-        if (!encodings.empty()) {
-          transceivers()
-              ->StableState(transceiver_ext)
-              ->SetInitSendEncodings(encodings);
+    if (ConfiguredForMedia()) {
+      // We must use List and not ListInternal here because
+      // transceivers()->StableState() is indexed by the non-internal refptr.
+      for (const auto& transceiver_ext : transceivers()->List()) {
+        auto transceiver = transceiver_ext->internal();
+        if (transceiver->stopped()) {
+          continue;
+        }
+        const ContentInfo* content =
+            FindMediaSectionForTransceiver(transceiver, local_description());
+        if (!content) {
+          continue;
+        }
+        cricket::ChannelInterface* channel = transceiver->channel();
+        if (content->rejected || !channel || channel->local_streams().empty()) {
+          // 0 is a special value meaning "this sender has no associated send
+          // stream". Need to call this so the sender won't attempt to configure
+          // a no longer existing stream and run into DCHECKs in the lower
+          // layers.
+          transceiver->sender_internal()->SetSsrc(0);
+        } else {
+          // Get the StreamParams from the channel which could generate SSRCs.
+          const std::vector<StreamParams>& streams = channel->local_streams();
+          transceiver->sender_internal()->set_stream_ids(
+              streams[0].stream_ids());
+          auto encodings =
+              transceiver->sender_internal()->init_send_encodings();
+          transceiver->sender_internal()->SetSsrc(streams[0].first_ssrc());
+          if (!encodings.empty()) {
+            transceivers()
+                ->StableState(transceiver_ext)
+                ->SetInitSendEncodings(encodings);
+          }
         }
       }
     }
@@ -1930,6 +1938,9 @@
     SdpType sdp_type) {
   RTC_DCHECK_RUN_ON(signaling_thread());
   RTC_DCHECK(IsUnifiedPlan());
+  if (!ConfiguredForMedia()) {
+    return;
+  }
   std::vector<rtc::scoped_refptr<RtpTransceiverInterface>>
       now_receiving_transceivers;
   std::vector<rtc::scoped_refptr<RtpTransceiverInterface>> remove_list;
@@ -2717,7 +2728,9 @@
   } else {
     RTC_DCHECK(type == SdpType::kAnswer);
     ChangeSignalingState(PeerConnectionInterface::kStable);
-    transceivers()->DiscardStableStates();
+    if (ConfiguredForMedia()) {
+      transceivers()->DiscardStableStates();
+    }
   }
 
   // Update internal objects according to the session description's media
@@ -3143,6 +3156,9 @@
     if (!cricket::GetFirstDataContent(description->description()->contents()))
       return true;
   }
+  if (!ConfiguredForMedia()) {
+    return false;
+  }
 
   // 5. For each transceiver in connection's set of transceivers, perform the
   // following checks:
@@ -3254,7 +3270,6 @@
       }
     }
   }
-
   // If all the preceding checks were performed and true was not returned,
   // nothing remains to be negotiated; return false.
   return false;
@@ -3833,38 +3848,43 @@
 void SdpOfferAnswerHandler::GetOptionsForPlanBOffer(
     const PeerConnectionInterface::RTCOfferAnswerOptions& offer_answer_options,
     cricket::MediaSessionOptions* session_options) {
-  // Figure out transceiver directional preferences.
-  bool send_audio =
-      !rtp_manager()->GetAudioTransceiver()->internal()->senders().empty();
-  bool send_video =
-      !rtp_manager()->GetVideoTransceiver()->internal()->senders().empty();
+  bool offer_new_data_description =
+      data_channel_controller()->HasDataChannels();
+  bool send_audio = false;
+  bool send_video = false;
+  bool recv_audio = false;
+  bool recv_video = false;
+  if (ConfiguredForMedia()) {
+    // Figure out transceiver directional preferences.
+    send_audio =
+        !rtp_manager()->GetAudioTransceiver()->internal()->senders().empty();
+    send_video =
+        !rtp_manager()->GetVideoTransceiver()->internal()->senders().empty();
 
-  // By default, generate sendrecv/recvonly m= sections.
-  bool recv_audio = true;
-  bool recv_video = true;
-
+    // By default, generate sendrecv/recvonly m= sections.
+    recv_audio = true;
+    recv_video = true;
+  }
   // By default, only offer a new m= section if we have media to send with it.
   bool offer_new_audio_description = send_audio;
   bool offer_new_video_description = send_video;
-  bool offer_new_data_description =
-      data_channel_controller()->HasDataChannels();
-
-  // The "offer_to_receive_X" options allow those defaults to be overridden.
-  if (offer_answer_options.offer_to_receive_audio !=
-      PeerConnectionInterface::RTCOfferAnswerOptions::kUndefined) {
-    recv_audio = (offer_answer_options.offer_to_receive_audio > 0);
-    offer_new_audio_description =
-        offer_new_audio_description ||
-        (offer_answer_options.offer_to_receive_audio > 0);
+  if (ConfiguredForMedia()) {
+    // The "offer_to_receive_X" options allow those defaults to be overridden.
+    if (offer_answer_options.offer_to_receive_audio !=
+        PeerConnectionInterface::RTCOfferAnswerOptions::kUndefined) {
+      recv_audio = (offer_answer_options.offer_to_receive_audio > 0);
+      offer_new_audio_description =
+          offer_new_audio_description ||
+          (offer_answer_options.offer_to_receive_audio > 0);
+    }
+    if (offer_answer_options.offer_to_receive_video !=
+        RTCOfferAnswerOptions::kUndefined) {
+      recv_video = (offer_answer_options.offer_to_receive_video > 0);
+      offer_new_video_description =
+          offer_new_video_description ||
+          (offer_answer_options.offer_to_receive_video > 0);
+    }
   }
-  if (offer_answer_options.offer_to_receive_video !=
-      RTCOfferAnswerOptions::kUndefined) {
-    recv_video = (offer_answer_options.offer_to_receive_video > 0);
-    offer_new_video_description =
-        offer_new_video_description ||
-        (offer_answer_options.offer_to_receive_video > 0);
-  }
-
   absl::optional<size_t> audio_index;
   absl::optional<size_t> video_index;
   absl::optional<size_t> data_index;
@@ -3879,42 +3899,44 @@
         &audio_index, &video_index, &data_index, session_options);
   }
 
-  // Add audio/video/data m= sections to the end if needed.
-  if (!audio_index && offer_new_audio_description) {
-    cricket::MediaDescriptionOptions options(
-        cricket::MEDIA_TYPE_AUDIO, cricket::CN_AUDIO,
-        RtpTransceiverDirectionFromSendRecv(send_audio, recv_audio), false);
-    options.header_extensions =
-        media_engine()->voice().GetRtpHeaderExtensions();
-    session_options->media_description_options.push_back(options);
-    audio_index = session_options->media_description_options.size() - 1;
-  }
-  if (!video_index && offer_new_video_description) {
-    cricket::MediaDescriptionOptions options(
-        cricket::MEDIA_TYPE_VIDEO, cricket::CN_VIDEO,
-        RtpTransceiverDirectionFromSendRecv(send_video, recv_video), false);
-    options.header_extensions =
-        media_engine()->video().GetRtpHeaderExtensions();
-    session_options->media_description_options.push_back(options);
-    video_index = session_options->media_description_options.size() - 1;
+  if (ConfiguredForMedia()) {
+    // Add audio/video/data m= sections to the end if needed.
+    if (!audio_index && offer_new_audio_description) {
+      cricket::MediaDescriptionOptions options(
+          cricket::MEDIA_TYPE_AUDIO, cricket::CN_AUDIO,
+          RtpTransceiverDirectionFromSendRecv(send_audio, recv_audio), false);
+      options.header_extensions =
+          media_engine()->voice().GetRtpHeaderExtensions();
+      session_options->media_description_options.push_back(options);
+      audio_index = session_options->media_description_options.size() - 1;
+    }
+    if (!video_index && offer_new_video_description) {
+      cricket::MediaDescriptionOptions options(
+          cricket::MEDIA_TYPE_VIDEO, cricket::CN_VIDEO,
+          RtpTransceiverDirectionFromSendRecv(send_video, recv_video), false);
+      options.header_extensions =
+          media_engine()->video().GetRtpHeaderExtensions();
+      session_options->media_description_options.push_back(options);
+      video_index = session_options->media_description_options.size() - 1;
+    }
+    cricket::MediaDescriptionOptions* audio_media_description_options =
+        !audio_index
+            ? nullptr
+            : &session_options->media_description_options[*audio_index];
+    cricket::MediaDescriptionOptions* video_media_description_options =
+        !video_index
+            ? nullptr
+            : &session_options->media_description_options[*video_index];
+
+    AddPlanBRtpSenderOptions(rtp_manager()->GetSendersInternal(),
+                             audio_media_description_options,
+                             video_media_description_options,
+                             offer_answer_options.num_simulcast_layers);
   }
   if (!data_index && offer_new_data_description) {
     session_options->media_description_options.push_back(
         GetMediaDescriptionOptionsForActiveData(cricket::CN_DATA));
-    data_index = session_options->media_description_options.size() - 1;
   }
-
-  cricket::MediaDescriptionOptions* audio_media_description_options =
-      !audio_index ? nullptr
-                   : &session_options->media_description_options[*audio_index];
-  cricket::MediaDescriptionOptions* video_media_description_options =
-      !video_index ? nullptr
-                   : &session_options->media_description_options[*video_index];
-
-  AddPlanBRtpSenderOptions(rtp_manager()->GetSendersInternal(),
-                           audio_media_description_options,
-                           video_media_description_options,
-                           offer_answer_options.num_simulcast_layers);
 }
 
 void SdpOfferAnswerHandler::GetOptionsForUnifiedPlanOffer(
@@ -4020,27 +4042,29 @@
   // and not associated). Reuse media sections marked as recyclable first,
   // otherwise append to the end of the offer. New media sections should be
   // added in the order they were added to the PeerConnection.
-  for (const auto& transceiver : transceivers()->ListInternal()) {
-    if (transceiver->mid() || transceiver->stopping()) {
-      continue;
+  if (ConfiguredForMedia()) {
+    for (const auto& transceiver : transceivers()->ListInternal()) {
+      if (transceiver->mid() || transceiver->stopping()) {
+        continue;
+      }
+      size_t mline_index;
+      if (!recycleable_mline_indices.empty()) {
+        mline_index = recycleable_mline_indices.front();
+        recycleable_mline_indices.pop();
+        session_options->media_description_options[mline_index] =
+            GetMediaDescriptionOptionsForTransceiver(
+                transceiver, mid_generator_.GenerateString(),
+                /*is_create_offer=*/true);
+      } else {
+        mline_index = session_options->media_description_options.size();
+        session_options->media_description_options.push_back(
+            GetMediaDescriptionOptionsForTransceiver(
+                transceiver, mid_generator_.GenerateString(),
+                /*is_create_offer=*/true));
+      }
+      // See comment above for why CreateOffer changes the transceiver's state.
+      transceiver->set_mline_index(mline_index);
     }
-    size_t mline_index;
-    if (!recycleable_mline_indices.empty()) {
-      mline_index = recycleable_mline_indices.front();
-      recycleable_mline_indices.pop();
-      session_options->media_description_options[mline_index] =
-          GetMediaDescriptionOptionsForTransceiver(
-              transceiver, mid_generator_.GenerateString(),
-              /*is_create_offer=*/true);
-    } else {
-      mline_index = session_options->media_description_options.size();
-      session_options->media_description_options.push_back(
-          GetMediaDescriptionOptionsForTransceiver(
-              transceiver, mid_generator_.GenerateString(),
-              /*is_create_offer=*/true));
-    }
-    // See comment above for why CreateOffer changes the transceiver's state.
-    transceiver->set_mline_index(mline_index);
   }
   // Lastly, add a m-section if we have local data channels and an m section
   // does not already exist.
@@ -4080,25 +4104,32 @@
 void SdpOfferAnswerHandler::GetOptionsForPlanBAnswer(
     const PeerConnectionInterface::RTCOfferAnswerOptions& offer_answer_options,
     cricket::MediaSessionOptions* session_options) {
-  // Figure out transceiver directional preferences.
-  bool send_audio =
-      !rtp_manager()->GetAudioTransceiver()->internal()->senders().empty();
-  bool send_video =
-      !rtp_manager()->GetVideoTransceiver()->internal()->senders().empty();
+  bool send_audio = false;
+  bool recv_audio = false;
+  bool send_video = false;
+  bool recv_video = false;
 
-  // By default, generate sendrecv/recvonly m= sections. The direction is also
-  // restricted by the direction in the offer.
-  bool recv_audio = true;
-  bool recv_video = true;
+  if (ConfiguredForMedia()) {
+    // Figure out transceiver directional preferences.
+    send_audio =
+        !rtp_manager()->GetAudioTransceiver()->internal()->senders().empty();
+    send_video =
+        !rtp_manager()->GetVideoTransceiver()->internal()->senders().empty();
 
-  // The "offer_to_receive_X" options allow those defaults to be overridden.
-  if (offer_answer_options.offer_to_receive_audio !=
-      RTCOfferAnswerOptions::kUndefined) {
-    recv_audio = (offer_answer_options.offer_to_receive_audio > 0);
-  }
-  if (offer_answer_options.offer_to_receive_video !=
-      RTCOfferAnswerOptions::kUndefined) {
-    recv_video = (offer_answer_options.offer_to_receive_video > 0);
+    // By default, generate sendrecv/recvonly m= sections. The direction is also
+    // restricted by the direction in the offer.
+    recv_audio = true;
+    recv_video = true;
+
+    // The "offer_to_receive_X" options allow those defaults to be overridden.
+    if (offer_answer_options.offer_to_receive_audio !=
+        RTCOfferAnswerOptions::kUndefined) {
+      recv_audio = (offer_answer_options.offer_to_receive_audio > 0);
+    }
+    if (offer_answer_options.offer_to_receive_video !=
+        RTCOfferAnswerOptions::kUndefined) {
+      recv_video = (offer_answer_options.offer_to_receive_video > 0);
+    }
   }
 
   absl::optional<size_t> audio_index;
@@ -4121,10 +4152,12 @@
       !video_index ? nullptr
                    : &session_options->media_description_options[*video_index];
 
-  AddPlanBRtpSenderOptions(rtp_manager()->GetSendersInternal(),
-                           audio_media_description_options,
-                           video_media_description_options,
-                           offer_answer_options.num_simulcast_layers);
+  if (ConfiguredForMedia()) {
+    AddPlanBRtpSenderOptions(rtp_manager()->GetSendersInternal(),
+                             audio_media_description_options,
+                             video_media_description_options,
+                             offer_answer_options.num_simulcast_layers);
+  }
 }
 
 void SdpOfferAnswerHandler::GetOptionsForUnifiedPlanAnswer(
@@ -4469,6 +4502,9 @@
 void SdpOfferAnswerHandler::EnableSending() {
   TRACE_EVENT0("webrtc", "SdpOfferAnswerHandler::EnableSending");
   RTC_DCHECK_RUN_ON(signaling_thread());
+  if (!ConfiguredForMedia()) {
+    return;
+  }
   for (const auto& transceiver : transceivers()->ListInternal()) {
     cricket::ChannelInterface* channel = transceiver->channel();
     if (channel) {
@@ -4489,60 +4525,63 @@
   RTC_DCHECK_RUN_ON(signaling_thread());
   RTC_DCHECK(sdesc);
 
-  // Note: This will perform an Invoke over to the worker thread, which we'll
-  // also do in a loop below.
-  if (!UpdatePayloadTypeDemuxingState(source, bundle_groups_by_mid)) {
-    // Note that this is never expected to fail, since RtpDemuxer doesn't return
-    // an error when changing payload type demux criteria, which is all this
-    // does.
-    return RTCError(RTCErrorType::INTERNAL_ERROR,
-                    "Failed to update payload type demuxing state.");
-  }
-
-  // Push down the new SDP media section for each audio/video transceiver.
-  auto rtp_transceivers = transceivers()->ListInternal();
-  std::vector<
-      std::pair<cricket::ChannelInterface*, const MediaContentDescription*>>
-      channels;
-  for (const auto& transceiver : rtp_transceivers) {
-    const ContentInfo* content_info =
-        FindMediaSectionForTransceiver(transceiver, sdesc);
-    cricket::ChannelInterface* channel = transceiver->channel();
-    if (!channel || !content_info || content_info->rejected) {
-      continue;
-    }
-    const MediaContentDescription* content_desc =
-        content_info->media_description();
-    if (!content_desc) {
-      continue;
+  if (ConfiguredForMedia()) {
+    // Note: This will perform an Invoke over to the worker thread, which we'll
+    // also do in a loop below.
+    if (!UpdatePayloadTypeDemuxingState(source, bundle_groups_by_mid)) {
+      // Note that this is never expected to fail, since RtpDemuxer doesn't
+      // return an error when changing payload type demux criteria, which is all
+      // this does.
+      return RTCError(RTCErrorType::INTERNAL_ERROR,
+                      "Failed to update payload type demuxing state.");
     }
 
-    transceiver->OnNegotiationUpdate(type, content_desc);
-    channels.push_back(std::make_pair(channel, content_desc));
-  }
+    // Push down the new SDP media section for each audio/video transceiver.
+    auto rtp_transceivers = transceivers()->ListInternal();
+    std::vector<
+        std::pair<cricket::ChannelInterface*, const MediaContentDescription*>>
+        channels;
+    for (const auto& transceiver : rtp_transceivers) {
+      const ContentInfo* content_info =
+          FindMediaSectionForTransceiver(transceiver, sdesc);
+      cricket::ChannelInterface* channel = transceiver->channel();
+      if (!channel || !content_info || content_info->rejected) {
+        continue;
+      }
+      const MediaContentDescription* content_desc =
+          content_info->media_description();
+      if (!content_desc) {
+        continue;
+      }
 
-  // This for-loop of invokes helps audio impairment during re-negotiations.
-  // One of the causes is that downstairs decoder creation is synchronous at the
-  // moment, and that a decoder is created for each codec listed in the SDP.
-  //
-  // TODO(bugs.webrtc.org/12840): consider merging the invokes again after
-  // these projects have shipped:
-  // - bugs.webrtc.org/12462
-  // - crbug.com/1157227
-  // - crbug.com/1187289
-  for (const auto& entry : channels) {
-    std::string error;
-    bool success =
-        context_->worker_thread()->Invoke<bool>(RTC_FROM_HERE, [&]() {
-          return (source == cricket::CS_LOCAL)
-                     ? entry.first->SetLocalContent(entry.second, type, error)
-                     : entry.first->SetRemoteContent(entry.second, type, error);
-        });
-    if (!success) {
-      return RTCError(RTCErrorType::INVALID_PARAMETER, error);
+      transceiver->OnNegotiationUpdate(type, content_desc);
+      channels.push_back(std::make_pair(channel, content_desc));
+    }
+
+    // This for-loop of invokes helps audio impairment during re-negotiations.
+    // One of the causes is that downstairs decoder creation is synchronous at
+    // the moment, and that a decoder is created for each codec listed in the
+    // SDP.
+    //
+    // TODO(bugs.webrtc.org/12840): consider merging the invokes again after
+    // these projects have shipped:
+    // - bugs.webrtc.org/12462
+    // - crbug.com/1157227
+    // - crbug.com/1187289
+    for (const auto& entry : channels) {
+      std::string error;
+      bool success =
+          context_->worker_thread()->Invoke<bool>(RTC_FROM_HERE, [&]() {
+            return (source == cricket::CS_LOCAL)
+                       ? entry.first->SetLocalContent(entry.second, type, error)
+                       : entry.first->SetRemoteContent(entry.second, type,
+                                                       error);
+          });
+      if (!success) {
+        return RTCError(RTCErrorType::INVALID_PARAMETER, error);
+      }
     }
   }
-
   // Need complete offer/answer with an SCTP m= section before starting SCTP,
   // according to https://tools.ietf.org/html/draft-ietf-mmusic-sctp-sdp-19
   if (pc_->sctp_mid() && local_description() && remote_description()) {
@@ -4596,6 +4635,9 @@
   //           run the following steps:
   if (!IsUnifiedPlan())
     return;
+  if (!ConfiguredForMedia()) {
+    return;
+  }
   // Traverse a copy of the transceiver list.
   auto transceiver_list = transceivers()->List();
   for (auto transceiver : transceiver_list) {
@@ -4630,18 +4672,21 @@
 void SdpOfferAnswerHandler::RemoveUnusedChannels(
     const SessionDescription* desc) {
   RTC_DCHECK_RUN_ON(signaling_thread());
-  // Destroy video channel first since it may have a pointer to the
-  // voice channel.
-  const cricket::ContentInfo* video_info = cricket::GetFirstVideoContent(desc);
-  if (!video_info || video_info->rejected) {
-    rtp_manager()->GetVideoTransceiver()->internal()->ClearChannel();
-  }
+  if (ConfiguredForMedia()) {
+    // Destroy video channel first since it may have a pointer to the
+    // voice channel.
+    const cricket::ContentInfo* video_info =
+        cricket::GetFirstVideoContent(desc);
+    if (!video_info || video_info->rejected) {
+      rtp_manager()->GetVideoTransceiver()->internal()->ClearChannel();
+    }
 
-  const cricket::ContentInfo* audio_info = cricket::GetFirstAudioContent(desc);
-  if (!audio_info || audio_info->rejected) {
-    rtp_manager()->GetAudioTransceiver()->internal()->ClearChannel();
+    const cricket::ContentInfo* audio_info =
+        cricket::GetFirstAudioContent(desc);
+    if (!audio_info || audio_info->rejected) {
+      rtp_manager()->GetAudioTransceiver()->internal()->ClearChannel();
+    }
   }
-
   const cricket::ContentInfo* data_info = cricket::GetFirstDataContent(desc);
   if (!data_info) {
     RTCError error(RTCErrorType::OPERATION_ERROR_WITH_DATA,
@@ -5200,4 +5245,8 @@
       });
 }
 
+bool SdpOfferAnswerHandler::ConfiguredForMedia() const {
+  return context_->media_engine();
+}
+
 }  // namespace webrtc
diff --git a/pc/sdp_offer_answer.h b/pc/sdp_offer_answer.h
index ab3dc20..6a0aaaa 100644
--- a/pc/sdp_offer_answer.h
+++ b/pc/sdp_offer_answer.h
@@ -478,7 +478,7 @@
   // This enables media to flow on all configured audio/video channels.
   void EnableSending();
   // Push the media parts of the local or remote session description
-  // down to all of the channels.
+  // down to all of the channels, and start SCTP if needed.
   RTCError PushdownMediaDescription(
       SdpType type,
       cricket::ContentSource source,
@@ -596,6 +596,7 @@
   // ===================================================================
   const cricket::AudioOptions& audio_options() { return audio_options_; }
   const cricket::VideoOptions& video_options() { return video_options_; }
+  bool ConfiguredForMedia() const;
 
   PeerConnectionSdpMethods* const pc_;
   ConnectionContext* const context_;
diff --git a/pc/test/integration_test_helpers.h b/pc/test/integration_test_helpers.h
index 35aedbd..a1d3a54 100644
--- a/pc/test/integration_test_helpers.h
+++ b/pc/test/integration_test_helpers.h
@@ -373,9 +373,17 @@
   rtc::scoped_refptr<RtpSenderInterface> AddTrack(
       rtc::scoped_refptr<MediaStreamTrackInterface> track,
       const std::vector<std::string>& stream_ids = {}) {
+    EXPECT_TRUE(track);
+    if (!track) {
+      return nullptr;
+    }
     auto result = pc()->AddTrack(track, stream_ids);
     EXPECT_EQ(RTCErrorType::NONE, result.error().type());
-    return result.MoveValue();
+    if (result.ok()) {
+      return result.MoveValue();
+    } else {
+      return nullptr;
+    }
   }
 
   std::vector<rtc::scoped_refptr<RtpReceiverInterface>> GetReceiversOfType(