diff --git a/media/engine/webrtc_video_engine.cc b/media/engine/webrtc_video_engine.cc
index 2ec6b48..84f756c 100644
--- a/media/engine/webrtc_video_engine.cc
+++ b/media/engine/webrtc_video_engine.cc
@@ -47,6 +47,7 @@
 namespace {
 
 const int kMinLayerSize = 16;
+constexpr int64_t kUnsignaledSsrcCooldownMs = rtc::kNumMillisecsPerSec / 2;
 
 const char* StreamTypeToString(
     webrtc::VideoSendStream::StreamStats::StreamType type) {
@@ -1565,6 +1566,7 @@
   RTC_DCHECK_RUN_ON(&thread_checker_);
   RTC_LOG(LS_INFO) << "ResetUnsignaledRecvStream.";
   unsignaled_stream_params_ = StreamParams();
+  last_unsignalled_ssrc_creation_time_ms_ = absl::nullopt;
 
   // Delete any created default streams. This is needed to avoid SSRC collisions
   // in Call's RtpDemuxer, in the case that |this| has created a default video
@@ -1767,7 +1769,23 @@
         if (demuxer_criteria_id_ != demuxer_criteria_completed_id_) {
           return;
         }
-
+        // Ignore unknown ssrcs if we recently created an unsignalled receive
+        // stream since this shouldn't happen frequently. Getting into a state
+        // of creating decoders on every packet eats up processing time (e.g.
+        // https://crbug.com/1069603) and this cooldown prevents that.
+        if (last_unsignalled_ssrc_creation_time_ms_.has_value()) {
+          int64_t now_ms = rtc::TimeMillis();
+          if (now_ms - last_unsignalled_ssrc_creation_time_ms_.value() <
+              kUnsignaledSsrcCooldownMs) {
+            // We've already created an unsignalled ssrc stream within the last
+            // 0.5 s, ignore with a warning.
+            RTC_LOG(LS_WARNING)
+                << "Another unsignalled ssrc packet arrived shortly after the "
+                << "creation of an unsignalled ssrc stream. Dropping packet.";
+            return;
+          }
+        }
+        // Let the unsignalled ssrc handler decide whether to drop or deliver.
         switch (unsignalled_ssrc_handler_->OnUnsignalledSsrc(this, ssrc)) {
           case UnsignalledSsrcHandler::kDropPacket:
             return;
@@ -1780,6 +1798,7 @@
             webrtc::PacketReceiver::DELIVERY_OK) {
           RTC_LOG(LS_WARNING) << "Failed to deliver RTP packet on re-delivery.";
         }
+        last_unsignalled_ssrc_creation_time_ms_ = rtc::TimeMillis();
       }));
 }
 
diff --git a/media/engine/webrtc_video_engine.h b/media/engine/webrtc_video_engine.h
index e8125e1..cd6fbe5 100644
--- a/media/engine/webrtc_video_engine.h
+++ b/media/engine/webrtc_video_engine.h
@@ -588,6 +588,8 @@
   //   is a risk of receiving ssrcs for other, recently added m= sections.
   uint32_t demuxer_criteria_id_ RTC_GUARDED_BY(thread_checker_) = 0;
   uint32_t demuxer_criteria_completed_id_ RTC_GUARDED_BY(thread_checker_) = 0;
+  absl::optional<int64_t> last_unsignalled_ssrc_creation_time_ms_
+      RTC_GUARDED_BY(thread_checker_);
   std::set<uint32_t> send_ssrcs_ RTC_GUARDED_BY(thread_checker_);
   std::set<uint32_t> receive_ssrcs_ RTC_GUARDED_BY(thread_checker_);
 
diff --git a/media/engine/webrtc_video_engine_unittest.cc b/media/engine/webrtc_video_engine_unittest.cc
index 4805e97..336e157 100644
--- a/media/engine/webrtc_video_engine_unittest.cc
+++ b/media/engine/webrtc_video_engine_unittest.cc
@@ -97,6 +97,7 @@
 static const uint32_t kRtxSsrcs1[] = {4};
 static const uint32_t kFlexfecSsrc = 5;
 static const uint32_t kIncomingUnsignalledSsrc = 0xC0FFEE;
+static const int64_t kUnsignalledReceiveStreamCooldownMs = 500;
 
 constexpr uint32_t kRtpHeaderSize = 12;
 
@@ -2565,6 +2566,16 @@
 
   cricket::VideoCodec DefaultCodec() { return GetEngineCodec("VP8"); }
 
+  // After receciving and processing the packet, enough time is advanced that
+  // the unsignalled receive stream cooldown is no longer in effect.
+  void ReceivePacketAndAdvanceTime(rtc::CopyOnWriteBuffer packet,
+                                   int64_t packet_time_us) {
+    channel_->OnPacketReceived(packet, packet_time_us);
+    rtc::Thread::Current()->ProcessMessages(0);
+    fake_clock_.AdvanceTime(
+        webrtc::TimeDelta::Millis(kUnsignalledReceiveStreamCooldownMs));
+  }
+
  protected:
   FakeVideoSendStream* AddSendStream() {
     return AddSendStream(StreamParams::CreateLegacy(++last_ssrc_));
@@ -6297,8 +6308,7 @@
   memset(data, 0, sizeof(data));
   rtc::SetBE32(&data[8], ssrcs[0]);
   rtc::CopyOnWriteBuffer packet(data, kDataLength);
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
 
   ASSERT_EQ(1u, fake_call_->GetVideoReceiveStreams().size())
       << "No default receive stream created.";
@@ -6459,8 +6469,7 @@
   memset(data, 0, sizeof(data));
   rtc::SetBE32(&data[8], kIncomingUnsignalledSsrc);
   rtc::CopyOnWriteBuffer packet(data, kDataLength);
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
 
   // The stream should now be created with the appropriate sync label.
   EXPECT_EQ(1u, fake_call_->GetVideoReceiveStreams().size());
@@ -6475,16 +6484,14 @@
 
   // Until the demuxer criteria has been updated, we ignore in-flight ssrcs of
   // the recently removed unsignaled receive stream.
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   EXPECT_EQ(0u, fake_call_->GetVideoReceiveStreams().size());
 
   // After the demuxer criteria has been updated, we should proceed to create
   // unsignalled receive streams. This time when a default video receive stream
   // is created it won't have a sync_group.
   channel_->OnDemuxerCriteriaUpdateComplete();
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   EXPECT_EQ(1u, fake_call_->GetVideoReceiveStreams().size());
   EXPECT_TRUE(
       fake_call_->GetVideoReceiveStreams()[0]->GetConfig().sync_group.empty());
@@ -6501,8 +6508,7 @@
   memset(data, 0, sizeof(data));
   rtc::SetBE32(&data[8], kIncomingUnsignalledSsrc);
   rtc::CopyOnWriteBuffer packet(data, kDataLength);
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
 
   // Default receive stream created.
   const auto& receivers1 = fake_call_->GetVideoReceiveStreams();
@@ -6552,7 +6558,7 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc1);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
   {
     // Receive a packet for kSsrc2.
@@ -6561,9 +6567,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc2);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
 
   // No unsignaled ssrc for kSsrc2 should have been created, but kSsrc1 should
   // arrive since it already has a stream.
@@ -6585,7 +6590,7 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc1);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
   {
     // Receive a packet for kSsrc2.
@@ -6594,9 +6599,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc2);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
 
   // An unsignalled ssrc for kSsrc2 should be created and the packet counter
   // should increase for both ssrcs.
@@ -6637,7 +6641,7 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc1);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
   {
     // Receive a packet for kSsrc2.
@@ -6646,9 +6650,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc2);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
 
   // No unsignaled ssrc for kSsrc1 should have been created, but the packet
   // count for kSsrc2 should increase.
@@ -6669,7 +6672,7 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc1);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
   {
     // Receive a packet for kSsrc2.
@@ -6678,9 +6681,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc2);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
 
   // An unsignalled ssrc for kSsrc1 should be created and the packet counter
   // should increase for both ssrcs.
@@ -6717,9 +6719,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
   EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc), 1u);
 
   // Signal that the demuxer knows about the first update: the removal.
@@ -6734,9 +6735,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
   EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc), 2u);
 
   // Remove the kSsrc again while previous demuxer updates are still pending.
@@ -6752,9 +6752,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
   EXPECT_EQ(fake_call_->GetVideoReceiveStreams().size(), 0u);
   EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc), 2u);
 
@@ -6770,9 +6769,8 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
-    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   }
-  rtc::Thread::Current()->ProcessMessages(0);
   EXPECT_EQ(fake_call_->GetVideoReceiveStreams().size(), 0u);
   EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc), 2u);
 
@@ -6788,11 +6786,72 @@
     memset(data, 0, sizeof(data));
     rtc::SetBE32(&data[8], kSsrc);
     rtc::CopyOnWriteBuffer packet(data, kDataLength);
+    ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
+  }
+  EXPECT_EQ(fake_call_->GetVideoReceiveStreams().size(), 1u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc), 3u);
+}
+
+TEST_F(WebRtcVideoChannelTest, UnsignalledSsrcHasACooldown) {
+  const uint32_t kSsrc1 = 1;
+  const uint32_t kSsrc2 = 2;
+
+  // Send packets for kSsrc1, creating an unsignalled receive stream.
+  {
+    // Receive a packet for kSsrc1.
+    const size_t kDataLength = 12;
+    uint8_t data[kDataLength];
+    memset(data, 0, sizeof(data));
+    rtc::SetBE32(&data[8], kSsrc1);
+    rtc::CopyOnWriteBuffer packet(data, kDataLength);
     channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
   }
   rtc::Thread::Current()->ProcessMessages(0);
+  fake_clock_.AdvanceTime(
+      webrtc::TimeDelta::Millis(kUnsignalledReceiveStreamCooldownMs - 1));
+
+  // We now have an unsignalled receive stream for kSsrc1.
   EXPECT_EQ(fake_call_->GetVideoReceiveStreams().size(), 1u);
-  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc), 3u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc1), 1u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc2), 0u);
+
+  {
+    // Receive a packet for kSsrc2.
+    const size_t kDataLength = 12;
+    uint8_t data[kDataLength];
+    memset(data, 0, sizeof(data));
+    rtc::SetBE32(&data[8], kSsrc2);
+    rtc::CopyOnWriteBuffer packet(data, kDataLength);
+    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+  }
+  rtc::Thread::Current()->ProcessMessages(0);
+
+  // Not enough time has passed to replace the unsignalled receive stream, so
+  // the kSsrc2 should be ignored.
+  EXPECT_EQ(fake_call_->GetVideoReceiveStreams().size(), 1u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc1), 1u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc2), 0u);
+
+  // After 500 ms, kSsrc2 should trigger a new unsignalled receive stream that
+  // replaces the old one.
+  fake_clock_.AdvanceTime(webrtc::TimeDelta::Millis(1));
+  {
+    // Receive a packet for kSsrc2.
+    const size_t kDataLength = 12;
+    uint8_t data[kDataLength];
+    memset(data, 0, sizeof(data));
+    rtc::SetBE32(&data[8], kSsrc2);
+    rtc::CopyOnWriteBuffer packet(data, kDataLength);
+    channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
+  }
+  rtc::Thread::Current()->ProcessMessages(0);
+
+  // The old unsignalled receive stream was destroyed and replaced, so we still
+  // only have one unsignalled receive stream. But tha packet counter for kSsrc2
+  // has now increased.
+  EXPECT_EQ(fake_call_->GetVideoReceiveStreams().size(), 1u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc1), 1u);
+  EXPECT_EQ(fake_call_->GetDeliveredPacketsForSsrc(kSsrc2), 1u);
 }
 
 // Test BaseMinimumPlayoutDelayMs on receive streams.
@@ -6828,8 +6887,7 @@
   memset(data, 0, sizeof(data));
   rtc::SetBE32(&data[8], kIncomingUnsignalledSsrc);
   rtc::CopyOnWriteBuffer packet(data, kDataLength);
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
 
   recv_stream = fake_call_->GetVideoReceiveStream(kIncomingUnsignalledSsrc);
   EXPECT_EQ(recv_stream->base_mininum_playout_delay_ms(), 200);
@@ -6866,8 +6924,7 @@
   rtc::Set8(data, 1, payload_type);
   rtc::SetBE32(&data[8], kIncomingUnsignalledSsrc);
   rtc::CopyOnWriteBuffer packet(data, kDataLength);
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
 
   if (expect_created_receive_stream) {
     EXPECT_EQ(1u, fake_call_->GetVideoReceiveStreams().size())
@@ -6954,8 +7011,7 @@
   rtpHeader.ssrc = kIncomingUnsignalledSsrc + 1;
   cricket::SetRtpHeader(data, sizeof(data), rtpHeader);
   rtc::CopyOnWriteBuffer packet(data, sizeof(data));
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   // VP8 packet should create default receive stream.
   ASSERT_EQ(1u, fake_call_->GetVideoReceiveStreams().size());
   FakeVideoReceiveStream* recv_stream = fake_call_->GetVideoReceiveStreams()[0];
@@ -6976,8 +7032,7 @@
   rtpHeader.ssrc = kIncomingUnsignalledSsrc + 2;
   cricket::SetRtpHeader(data, sizeof(data), rtpHeader);
   rtc::CopyOnWriteBuffer packet2(data, sizeof(data));
-  channel_->OnPacketReceived(packet2, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet2, /* packet_time_us */ -1);
   // VP9 packet should replace the default receive SSRC.
   ASSERT_EQ(1u, fake_call_->GetVideoReceiveStreams().size());
   recv_stream = fake_call_->GetVideoReceiveStreams()[0];
@@ -6999,8 +7054,7 @@
   rtpHeader.ssrc = kIncomingUnsignalledSsrc + 3;
   cricket::SetRtpHeader(data, sizeof(data), rtpHeader);
   rtc::CopyOnWriteBuffer packet3(data, sizeof(data));
-  channel_->OnPacketReceived(packet3, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet3, /* packet_time_us */ -1);
   // H264 packet should replace the default receive SSRC.
   ASSERT_EQ(1u, fake_call_->GetVideoReceiveStreams().size());
   recv_stream = fake_call_->GetVideoReceiveStreams()[0];
@@ -7039,8 +7093,7 @@
   rtp_header.ssrc = kSsrcs3[0];
   cricket::SetRtpHeader(data, sizeof(data), rtp_header);
   rtc::CopyOnWriteBuffer packet(data, sizeof(data));
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   // Default receive stream should be created.
   ASSERT_EQ(1u, fake_call_->GetVideoReceiveStreams().size());
   FakeVideoReceiveStream* recv_stream0 =
@@ -7058,8 +7111,7 @@
   rtp_header.ssrc = kSsrcs3[1];
   cricket::SetRtpHeader(data, sizeof(data), rtp_header);
   packet.SetData(data, sizeof(data));
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
   // New default receive stream should be created, but old stream should remain.
   ASSERT_EQ(2u, fake_call_->GetVideoReceiveStreams().size());
   EXPECT_EQ(recv_stream0, fake_call_->GetVideoReceiveStreams()[0]);
@@ -8672,8 +8724,7 @@
   rtpHeader.ssrc = kIncomingUnsignalledSsrc;
   cricket::SetRtpHeader(data, sizeof(data), rtpHeader);
   rtc::CopyOnWriteBuffer packet(data, sizeof(data));
-  channel_->OnPacketReceived(packet, /* packet_time_us */ -1);
-  rtc::Thread::Current()->ProcessMessages(0);
+  ReceivePacketAndAdvanceTime(packet, /* packet_time_us */ -1);
 
   // The |ssrc| member should still be unset.
   rtp_parameters = channel_->GetDefaultRtpReceiveParameters();