commit fedc7ab1f26d4bea69cd712dced8cc6e871c58ba
author Philipp Hancke <phancke@nvidia.com> Tue Nov 17 20:59:12 2020
committer Commit Bot <commit-bot@chromium.org> Wed Nov 18 09:04:52 2020
tree f17977c8190ee79deffa67e0586e51adb4ed6a96
parent a4fd641f519b22c2c36878080939da1549f567cf

guard flexfec usage with fieldtrial

otherwise if the client receives a flexfec-enabled offer
and receiving flexfec is enabled by default, an answer
or subsequent offer will enable sending flexfec.

BUG=webrtc:8151

Change-Id: I632094f69ffa68518b6b8f31175eb093efaf51c6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/193862
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/master@{#32628}

pc/BUILD.gn

diff --git a/pc/BUILD.gn b/pc/BUILD.gn
index 10c5c7b..84aba07 100644
--- a/pc/BUILD.gn
+++ b/pc/BUILD.gn
@@ -803,6 +803,7 @@
       "../rtc_base:rtc_base_tests_utils",
       "../rtc_base/third_party/sigslot",
       "../system_wrappers:metrics",
+      "../test:field_trial",
       "../test:test_main",
       "../test:test_support",
       "//third_party/abseil-cpp/absl/algorithm:container",

pc/media_session.cc

diff --git a/pc/media_session.cc b/pc/media_session.cc
index cbff216..6d8a9a4 100644
--- a/pc/media_session.cc
+++ b/pc/media_session.cc
@@ -36,6 +36,7 @@
 #include "rtc_base/logging.h"
 #include "rtc_base/third_party/base64/base64.h"
 #include "rtc_base/unique_id_generator.h"
+#include "system_wrappers/include/field_trial.h"
 
 namespace {
 
@@ -336,6 +337,12 @@
            "a single media streams. This session has multiple "
            "media streams however, so no FlexFEC SSRC will be generated.";
   }
+  if (include_flexfec_stream &&
+      !webrtc::field_trial::IsEnabled("WebRTC-FlexFEC-03")) {
+    include_flexfec_stream = false;
+    RTC_LOG(LS_WARNING)
+        << "WebRTC-FlexFEC trial is not enabled, not sending FlexFEC";
+  }
 
   result.GenerateSsrcs(sender.num_sim_layers, include_rtx_streams,
                        include_flexfec_stream, ssrc_generator);

pc/media_session_unittest.cc

diff --git a/pc/media_session_unittest.cc b/pc/media_session_unittest.cc
index 5a9002b..d8cb159 100644
--- a/pc/media_session_unittest.cc
+++ b/pc/media_session_unittest.cc
@@ -34,6 +34,7 @@
 #include "rtc_base/ssl_adapter.h"
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/unique_id_generator.h"
+#include "test/field_trial.h"
 #include "test/gmock.h"
 
 #define ASSERT_CRYPTO(cd, s, cs)      \
@@ -3456,8 +3457,10 @@
 }
 
 // Test that, when the FlexFEC codec is added, a FlexFEC ssrc is created
-// together with a FEC-FR grouping.
+// together with a FEC-FR grouping. Guarded by WebRTC-FlexFEC-03 trial.
 TEST_F(MediaSessionDescriptionFactoryTest, GenerateFlexfecSsrc) {
+  webrtc::test::ScopedFieldTrials override_field_trials(
+      "WebRTC-FlexFEC-03/Enabled/");
   MediaSessionOptions opts;
   AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
                              RtpTransceiverDirection::kSendRecv, kActive,
@@ -3499,6 +3502,8 @@
 // TODO(brandtr): Remove this test when we support simulcast, either through
 // multiple FlexfecSenders, or through multistream protection.
 TEST_F(MediaSessionDescriptionFactoryTest, SimSsrcsGenerateNoFlexfecSsrcs) {
+  webrtc::test::ScopedFieldTrials override_field_trials(
+      "WebRTC-FlexFEC-03/Enabled/");
   MediaSessionOptions opts;
   AddMediaDescriptionOptions(MEDIA_TYPE_VIDEO, "video",
                              RtpTransceiverDirection::kSendRecv, kActive,