diff --git a/media/base/mediaconstants.cc b/media/base/mediaconstants.cc
index e3a1d9b1d4..abc4e0c1b9 100644
--- a/media/base/mediaconstants.cc
+++ b/media/base/mediaconstants.cc
@@ -112,4 +112,8 @@ const char kH264FmtpSpropParameterSets[] = "sprop-parameter-sets";
 const char kH264ProfileLevelConstrainedBaseline[] = "42e01f";
 
 const int kDefaultVideoMaxFramerate = 60;
+
+const size_t kConferenceMaxNumSpatialLayers = 3;
+const size_t kConferenceMaxNumTemporalLayers = 3;
+const size_t kConferenceDefaultNumTemporalLayers = 3;
 }  // namespace cricket
diff --git a/media/base/mediaconstants.h b/media/base/mediaconstants.h
index 73bbb8d247..72edd89e20 100644
--- a/media/base/mediaconstants.h
+++ b/media/base/mediaconstants.h
@@ -134,6 +134,10 @@ extern const char kH264FmtpSpropParameterSets[];
 extern const char kH264ProfileLevelConstrainedBaseline[];
 
 extern const int kDefaultVideoMaxFramerate;
+
+extern const size_t kConferenceMaxNumSpatialLayers;
+extern const size_t kConferenceMaxNumTemporalLayers;
+extern const size_t kConferenceDefaultNumTemporalLayers;
 }  // namespace cricket
 
 #endif  // MEDIA_BASE_MEDIACONSTANTS_H_
diff --git a/media/engine/webrtcvideoengine.cc b/media/engine/webrtcvideoengine.cc
index bc90c8fcf1..7174524dd7 100644
--- a/media/engine/webrtcvideoengine.cc
+++ b/media/engine/webrtcvideoengine.cc
@@ -340,43 +340,43 @@ static int GetMaxDefaultVideoBitrateKbps(int width, int height) {
   }
 }
 
-bool GetVp9LayersFromFieldTrialGroup(int* num_spatial_layers,
-                                     int* num_temporal_layers) {
+bool GetVp9LayersFromFieldTrialGroup(size_t* num_spatial_layers,
+                                     size_t* num_temporal_layers) {
   std::string group = webrtc::field_trial::FindFullName("WebRTC-SupportVP9SVC");
   if (group.empty())
     return false;
 
-  if (sscanf(group.c_str(), "EnabledByFlag_%dSL%dTL", num_spatial_layers,
+  if (sscanf(group.c_str(), "EnabledByFlag_%zuSL%zuTL", num_spatial_layers,
              num_temporal_layers) != 2) {
     return false;
   }
-  const int kMaxSpatialLayers = 2;
+  const size_t kMaxSpatialLayers = 3;
   if (*num_spatial_layers > kMaxSpatialLayers || *num_spatial_layers < 1)
     return false;
 
-  const int kMaxTemporalLayers = 3;
+  const size_t kMaxTemporalLayers = 3;
   if (*num_temporal_layers > kMaxTemporalLayers || *num_temporal_layers < 1)
     return false;
 
   return true;
 }
 
-int GetDefaultVp9SpatialLayers() {
-  int num_sl;
-  int num_tl;
+rtc::Optional<size_t> GetVp9SpatialLayersFromFieldTrial() {
+  size_t num_sl;
+  size_t num_tl;
   if (GetVp9LayersFromFieldTrialGroup(&num_sl, &num_tl)) {
     return num_sl;
   }
-  return 1;
+  return rtc::nullopt;
 }
 
-int GetDefaultVp9TemporalLayers() {
-  int num_sl;
-  int num_tl;
+rtc::Optional<size_t> GetVp9TemporalLayersFromFieldTrial() {
+  size_t num_sl;
+  size_t num_tl;
   if (GetVp9LayersFromFieldTrialGroup(&num_sl, &num_tl)) {
     return num_tl;
   }
-  return 1;
+  return rtc::nullopt;
 }
 
 const char kForcedFallbackFieldTrial[] =
@@ -464,8 +464,22 @@ WebRtcVideoChannel::WebRtcVideoSendStream::ConfigureVideoEncoderSettings(
       vp9_settings.numberOfSpatialLayers = 2;
       vp9_settings.numberOfTemporalLayers = 1;
     } else {
-      vp9_settings.numberOfSpatialLayers = GetDefaultVp9SpatialLayers();
-      vp9_settings.numberOfTemporalLayers = GetDefaultVp9TemporalLayers();
+      const size_t default_num_spatial_layers =
+          parameters_.config.rtp.ssrcs.size();
+      const size_t num_spatial_layers =
+          GetVp9SpatialLayersFromFieldTrial().value_or(
+              default_num_spatial_layers);
+
+      const size_t default_num_temporal_layers =
+          num_spatial_layers > 1 ? kConferenceDefaultNumTemporalLayers : 1;
+      const size_t num_temporal_layers =
+          GetVp9TemporalLayersFromFieldTrial().value_or(
+              default_num_temporal_layers);
+
+      vp9_settings.numberOfSpatialLayers = std::min<unsigned char>(
+          num_spatial_layers, kConferenceMaxNumSpatialLayers);
+      vp9_settings.numberOfTemporalLayers = std::min<unsigned char>(
+          num_temporal_layers, kConferenceMaxNumTemporalLayers);
     }
 
     // VP9 denoising is disabled by default.
diff --git a/media/engine/webrtcvideoengine_unittest.cc b/media/engine/webrtcvideoengine_unittest.cc
index e994d8d747..d0b570725a 100644
--- a/media/engine/webrtcvideoengine_unittest.cc
+++ b/media/engine/webrtcvideoengine_unittest.cc
@@ -2223,6 +2223,38 @@ TEST_F(Vp9SettingsTest, VerifyVp9SpecificSettings) {
   EXPECT_TRUE(channel_->SetVideoSend(last_ssrc_, true, nullptr, nullptr));
 }
 
+TEST_F(Vp9SettingsTest, MultipleSsrcsEnablesSvc) {
+  cricket::VideoSendParameters parameters;
+  parameters.codecs.push_back(GetEngineCodec("VP9"));
+  ASSERT_TRUE(channel_->SetSendParameters(parameters));
+
+  std::vector<uint32_t> ssrcs = MAKE_VECTOR(kSsrcs3);
+
+  FakeVideoSendStream* stream =
+      AddSendStream(CreateSimStreamParams("cname", ssrcs));
+
+  webrtc::VideoSendStream::Config config = stream->GetConfig().Copy();
+  EXPECT_EQ(ssrcs.size(), config.rtp.ssrcs.size());
+
+  FakeVideoCapturerWithTaskQueue capturer;
+  EXPECT_EQ(cricket::CS_RUNNING,
+            capturer.Start(capturer.GetSupportedFormats()->front()));
+  EXPECT_TRUE(channel_->SetVideoSend(ssrcs[0], true, nullptr, &capturer));
+  channel_->SetSend(true);
+
+  EXPECT_TRUE(capturer.CaptureFrame());
+
+  webrtc::VideoCodecVP9 vp9_settings;
+  ASSERT_TRUE(stream->GetVp9Settings(&vp9_settings)) << "No VP9 config set.";
+
+  const size_t kNumSpatialLayers = ssrcs.size();
+  const size_t kNumTemporalLayers = 3;
+  EXPECT_EQ(vp9_settings.numberOfSpatialLayers, kNumSpatialLayers);
+  EXPECT_EQ(vp9_settings.numberOfTemporalLayers, kNumTemporalLayers);
+
+  EXPECT_TRUE(channel_->SetVideoSend(ssrcs[0], true, nullptr, nullptr));
+}
+
 class Vp9SettingsTestWithFieldTrial : public Vp9SettingsTest {
  public:
   explicit Vp9SettingsTestWithFieldTrial(const char* field_trials)