diff --git a/audio/BUILD.gn b/audio/BUILD.gn
index bbc294b..09562b9 100644
--- a/audio/BUILD.gn
+++ b/audio/BUILD.gn
@@ -223,6 +223,7 @@
       "utility:utility_tests",
       "//testing/gtest",
     ]
+    absl_deps = [ "//third_party/abseil-cpp/absl/memory" ]
   }
 
   rtc_library("channel_receive_unittest") {
diff --git a/audio/channel_send.cc b/audio/channel_send.cc
index b71f564..ecf2cb5 100644
--- a/audio/channel_send.cc
+++ b/audio/channel_send.cc
@@ -169,7 +169,8 @@
                        uint8_t payloadType,
                        uint32_t rtp_timestamp_without_offset,
                        rtc::ArrayView<const uint8_t> payload,
-                       int64_t absolute_capture_timestamp_ms)
+                       int64_t absolute_capture_timestamp_ms,
+                       rtc::ArrayView<const uint32_t> csrcs)
       RTC_RUN_ON(encoder_queue_);
 
   void OnReceivedRtt(int64_t rtt_ms);
@@ -294,14 +295,15 @@
     return 0;
   }
   return SendRtpAudio(frameType, payloadType, rtp_timestamp, payload,
-                      absolute_capture_timestamp_ms);
+                      absolute_capture_timestamp_ms, /*csrcs=*/{});
 }
 
 int32_t ChannelSend::SendRtpAudio(AudioFrameType frameType,
                                   uint8_t payloadType,
                                   uint32_t rtp_timestamp_without_offset,
                                   rtc::ArrayView<const uint8_t> payload,
-                                  int64_t absolute_capture_timestamp_ms) {
+                                  int64_t absolute_capture_timestamp_ms,
+                                  rtc::ArrayView<const uint32_t> csrcs) {
   // E2EE Custom Audio Frame Encryption (This is optional).
   // Keep this buffer around for the lifetime of the send call.
   rtc::Buffer encrypted_audio_payload;
@@ -363,7 +365,8 @@
       .payload = payload,
       .payload_id = payloadType,
       .rtp_timestamp =
-          rtp_timestamp_without_offset + rtp_rtcp_->StartTimestamp()};
+          rtp_timestamp_without_offset + rtp_rtcp_->StartTimestamp(),
+      .csrcs = csrcs};
   if (absolute_capture_timestamp_ms > 0) {
     frame.capture_time = Timestamp::Millis(absolute_capture_timestamp_ms);
   }
@@ -859,12 +862,13 @@
       [this](AudioFrameType frameType, uint8_t payloadType,
              uint32_t rtp_timestamp_with_offset,
              rtc::ArrayView<const uint8_t> payload,
-             int64_t absolute_capture_timestamp_ms) {
+             int64_t absolute_capture_timestamp_ms,
+             rtc::ArrayView<const uint32_t> csrcs) {
         RTC_DCHECK_RUN_ON(&encoder_queue_);
         return SendRtpAudio(
             frameType, payloadType,
             rtp_timestamp_with_offset - rtp_rtcp_->StartTimestamp(), payload,
-            absolute_capture_timestamp_ms);
+            absolute_capture_timestamp_ms, csrcs);
       };
   frame_transformer_delegate_ =
       rtc::make_ref_counted<ChannelSendFrameTransformerDelegate>(
diff --git a/audio/channel_send_frame_transformer_delegate.cc b/audio/channel_send_frame_transformer_delegate.cc
index f66f29d..2eea0d2 100644
--- a/audio/channel_send_frame_transformer_delegate.cc
+++ b/audio/channel_send_frame_transformer_delegate.cc
@@ -11,6 +11,7 @@
 #include "audio/channel_send_frame_transformer_delegate.h"
 
 #include <utility>
+#include <vector>
 
 namespace webrtc {
 namespace {
@@ -56,6 +57,7 @@
       size_t payload_size,
       absl::optional<uint64_t> absolute_capture_timestamp_ms,
       uint32_t ssrc,
+      std::vector<uint32_t> csrcs,
       const std::string& codec_mime_type)
       : frame_type_(frame_type),
         payload_type_(payload_type),
@@ -63,6 +65,7 @@
         payload_(payload_data, payload_size),
         absolute_capture_timestamp_ms_(absolute_capture_timestamp_ms),
         ssrc_(ssrc),
+        csrcs_(std::move(csrcs)),
         codec_mime_type_(codec_mime_type) {}
   ~TransformableOutgoingAudioFrame() override = default;
   rtc::ArrayView<const uint8_t> GetData() const override { return payload_; }
@@ -81,7 +84,7 @@
   std::string GetMimeType() const override { return codec_mime_type_; }
 
   rtc::ArrayView<const uint32_t> GetContributingSources() const override {
-    return {};
+    return csrcs_;
   }
 
   const absl::optional<uint16_t> SequenceNumber() const override {
@@ -103,6 +106,7 @@
   rtc::Buffer payload_;
   absl::optional<uint64_t> absolute_capture_timestamp_ms_;
   uint32_t ssrc_;
+  std::vector<uint32_t> csrcs_;
   std::string codec_mime_type_;
 };
 }  // namespace
@@ -143,14 +147,15 @@
       send_frame_callback_(
           frame_type, payload_type, rtp_timestamp,
           rtc::ArrayView<const uint8_t>(payload_data, payload_size),
-          absolute_capture_timestamp_ms);
+          absolute_capture_timestamp_ms, /*csrcs=*/{});
       return;
     }
   }
   frame_transformer_->Transform(
       std::make_unique<TransformableOutgoingAudioFrame>(
           frame_type, payload_type, rtp_timestamp, payload_data, payload_size,
-          absolute_capture_timestamp_ms, ssrc, codec_mimetype));
+          absolute_capture_timestamp_ms, ssrc,
+          /*csrcs=*/std::vector<uint32_t>(), codec_mimetype));
 }
 
 void ChannelSendFrameTransformerDelegate::OnTransformedFrame(
@@ -184,17 +189,21 @@
       transformed_frame->GetData(),
       transformed_frame->AbsoluteCaptureTimestamp()
           ? *transformed_frame->AbsoluteCaptureTimestamp()
-          : 0);
+          : 0,
+      transformed_frame->GetContributingSources());
 }
 
 std::unique_ptr<TransformableAudioFrameInterface> CloneSenderAudioFrame(
     TransformableAudioFrameInterface* original) {
+  std::vector<uint32_t> csrcs;
+  csrcs.assign(original->GetContributingSources().begin(),
+               original->GetContributingSources().end());
   return std::make_unique<TransformableOutgoingAudioFrame>(
       InterfaceFrameTypeToInternalFrameType(original->Type()),
       original->GetPayloadType(), original->GetTimestamp(),
       original->GetData().data(), original->GetData().size(),
       original->AbsoluteCaptureTimestamp(), original->GetSsrc(),
-      original->GetMimeType());
+      std::move(csrcs), original->GetMimeType());
 }
 
 }  // namespace webrtc
diff --git a/audio/channel_send_frame_transformer_delegate.h b/audio/channel_send_frame_transformer_delegate.h
index bcec018..97fc14f 100644
--- a/audio/channel_send_frame_transformer_delegate.h
+++ b/audio/channel_send_frame_transformer_delegate.h
@@ -35,7 +35,8 @@
                             uint8_t payloadType,
                             uint32_t rtp_timestamp_with_offset,
                             rtc::ArrayView<const uint8_t> payload,
-                            int64_t absolute_capture_timestamp_ms)>;
+                            int64_t absolute_capture_timestamp_ms,
+                            rtc::ArrayView<const uint32_t> csrcs)>;
   ChannelSendFrameTransformerDelegate(
       SendFrameCallback send_frame_callback,
       rtc::scoped_refptr<FrameTransformerInterface> frame_transformer,
diff --git a/audio/channel_send_frame_transformer_delegate_unittest.cc b/audio/channel_send_frame_transformer_delegate_unittest.cc
index a47cbd5..4dcd15c 100644
--- a/audio/channel_send_frame_transformer_delegate_unittest.cc
+++ b/audio/channel_send_frame_transformer_delegate_unittest.cc
@@ -12,7 +12,9 @@
 
 #include <memory>
 #include <utility>
+#include <vector>
 
+#include "absl/memory/memory.h"
 #include "rtc_base/task_queue_for_test.h"
 #include "test/gmock.h"
 #include "test/gtest.h"
@@ -24,10 +26,13 @@
 
 using ::testing::_;
 using ::testing::ElementsAre;
+using ::testing::ElementsAreArray;
 using ::testing::NiceMock;
 using ::testing::Return;
 using ::testing::SaveArg;
 
+const uint8_t mock_data[] = {1, 2, 3, 4};
+
 class MockChannelSend {
  public:
   MockChannelSend() = default;
@@ -39,30 +44,56 @@
                uint8_t payloadType,
                uint32_t rtp_timestamp,
                rtc::ArrayView<const uint8_t> payload,
-               int64_t absolute_capture_timestamp_ms));
+               int64_t absolute_capture_timestamp_ms,
+               rtc::ArrayView<const uint32_t> csrcs));
 
   ChannelSendFrameTransformerDelegate::SendFrameCallback callback() {
     return [this](AudioFrameType frameType, uint8_t payloadType,
                   uint32_t rtp_timestamp, rtc::ArrayView<const uint8_t> payload,
-                  int64_t absolute_capture_timestamp_ms) {
+                  int64_t absolute_capture_timestamp_ms,
+                  rtc::ArrayView<const uint32_t> csrcs) {
       return SendFrame(frameType, payloadType, rtp_timestamp, payload,
-                       absolute_capture_timestamp_ms);
+                       absolute_capture_timestamp_ms, csrcs);
     };
   }
 };
 
-std::unique_ptr<MockTransformableAudioFrame> CreateMockReceiverFrame() {
-  const uint8_t mock_data[] = {1, 2, 3, 4};
+std::unique_ptr<TransformableAudioFrameInterface> CreateMockReceiverFrame(
+    std::vector<const uint32_t> csrcs) {
   std::unique_ptr<MockTransformableAudioFrame> mock_frame =
-      std::make_unique<MockTransformableAudioFrame>();
+      std::make_unique<NiceMock<MockTransformableAudioFrame>>();
   rtc::ArrayView<const uint8_t> payload(mock_data);
   ON_CALL(*mock_frame, GetData).WillByDefault(Return(payload));
   ON_CALL(*mock_frame, GetPayloadType).WillByDefault(Return(0));
   ON_CALL(*mock_frame, GetDirection)
       .WillByDefault(Return(TransformableFrameInterface::Direction::kReceiver));
+  ON_CALL(*mock_frame, GetContributingSources).WillByDefault(Return(csrcs));
   return mock_frame;
 }
 
+std::unique_ptr<TransformableAudioFrameInterface> CreateFrame() {
+  TaskQueueForTest channel_queue("channel_queue");
+  rtc::scoped_refptr<MockFrameTransformer> mock_frame_transformer =
+      rtc::make_ref_counted<NiceMock<MockFrameTransformer>>();
+  MockChannelSend mock_channel;
+  rtc::scoped_refptr<ChannelSendFrameTransformerDelegate> delegate =
+      rtc::make_ref_counted<ChannelSendFrameTransformerDelegate>(
+          mock_channel.callback(), mock_frame_transformer, &channel_queue);
+
+  std::unique_ptr<TransformableFrameInterface> frame;
+  ON_CALL(*mock_frame_transformer, Transform)
+      .WillByDefault(
+          [&frame](
+              std::unique_ptr<TransformableFrameInterface> transform_frame) {
+            frame = std::move(transform_frame);
+          });
+  delegate->Transform(AudioFrameType::kEmptyFrame, 0, 0, mock_data,
+                      sizeof(mock_data), 0,
+                      /*ssrc=*/0, /*mimeType=*/"audio/opus");
+  return absl::WrapUnique(
+      static_cast<webrtc::TransformableAudioFrameInterface*>(frame.release()));
+}
+
 // Test that the delegate registers itself with the frame transformer on Init().
 TEST(ChannelSendFrameTransformerDelegateTest,
      RegisterTransformedFrameCallbackOnInit) {
@@ -136,15 +167,16 @@
   delegate->Init();
   ASSERT_TRUE(callback);
 
-  const uint8_t data[] = {1, 2, 3, 4};
+  std::vector<const uint32_t> csrcs = {123, 234, 345, 456};
   EXPECT_CALL(mock_channel, SendFrame).Times(0);
-  EXPECT_CALL(mock_channel, SendFrame(_, 0, 0, ElementsAre(1, 2, 3, 4), _));
+  EXPECT_CALL(mock_channel, SendFrame(_, 0, 0, ElementsAreArray(mock_data), _,
+                                      ElementsAreArray(csrcs)));
   ON_CALL(*mock_frame_transformer, Transform)
-      .WillByDefault(
-          [&callback](std::unique_ptr<TransformableFrameInterface> frame) {
-            callback->OnTransformedFrame(CreateMockReceiverFrame());
-          });
-  delegate->Transform(AudioFrameType::kEmptyFrame, 0, 0, data, sizeof(data), 0,
+      .WillByDefault([&](std::unique_ptr<TransformableFrameInterface> frame) {
+        callback->OnTransformedFrame(CreateMockReceiverFrame(csrcs));
+      });
+  delegate->Transform(AudioFrameType::kEmptyFrame, 0, 0, mock_data,
+                      sizeof(mock_data), 0,
                       /*ssrc=*/0, /*mimeType=*/"audio/opus");
   channel_queue.WaitForPreviouslyPostedTasks();
 }
@@ -188,5 +220,39 @@
                       /*ssrc=*/0, /*mimeType=*/"audio/opus");
 }
 
+TEST(ChannelSendFrameTransformerDelegateTest,
+     CloningSenderFramePreservesInformation) {
+  std::unique_ptr<TransformableAudioFrameInterface> frame = CreateFrame();
+  std::unique_ptr<TransformableAudioFrameInterface> cloned_frame =
+      CloneSenderAudioFrame(frame.get());
+
+  EXPECT_EQ(cloned_frame->GetTimestamp(), frame->GetTimestamp());
+  EXPECT_EQ(cloned_frame->GetSsrc(), frame->GetSsrc());
+  EXPECT_EQ(cloned_frame->Type(), frame->Type());
+  EXPECT_EQ(cloned_frame->GetPayloadType(), frame->GetPayloadType());
+  EXPECT_EQ(cloned_frame->GetMimeType(), frame->GetMimeType());
+  EXPECT_THAT(cloned_frame->GetContributingSources(),
+              ElementsAreArray(frame->GetContributingSources()));
+}
+
+TEST(ChannelSendFrameTransformerDelegateTest, CloningReceiverFrameWithCsrcs) {
+  std::unique_ptr<TransformableAudioFrameInterface> frame =
+      CreateMockReceiverFrame(/*csrcs=*/{123, 234, 345});
+  std::unique_ptr<TransformableAudioFrameInterface> cloned_frame =
+      CloneSenderAudioFrame(frame.get());
+
+  EXPECT_EQ(cloned_frame->GetTimestamp(), frame->GetTimestamp());
+  EXPECT_EQ(cloned_frame->GetSsrc(), frame->GetSsrc());
+  EXPECT_EQ(cloned_frame->Type(), frame->Type());
+  EXPECT_EQ(cloned_frame->GetPayloadType(), frame->GetPayloadType());
+  EXPECT_EQ(cloned_frame->GetMimeType(), frame->GetMimeType());
+  EXPECT_EQ(cloned_frame->AbsoluteCaptureTimestamp(),
+            frame->AbsoluteCaptureTimestamp());
+
+  ASSERT_NE(frame->GetContributingSources().size(), 0u);
+  EXPECT_THAT(cloned_frame->GetContributingSources(),
+              ElementsAreArray(frame->GetContributingSources()));
+}
+
 }  // namespace
 }  // namespace webrtc
diff --git a/modules/rtp_rtcp/source/rtp_sender_audio.cc b/modules/rtp_rtcp/source/rtp_sender_audio.cc
index b826c30..9d2258d 100644
--- a/modules/rtp_rtcp/source/rtp_sender_audio.cc
+++ b/modules/rtp_rtcp/source/rtp_sender_audio.cc
@@ -254,7 +254,8 @@
     return false;
   }
 
-  std::unique_ptr<RtpPacketToSend> packet = rtp_sender_->AllocatePacket();
+  std::unique_ptr<RtpPacketToSend> packet =
+      rtp_sender_->AllocatePacket(frame.csrcs);
   packet->SetMarker(MarkerBit(frame.type, frame.payload_id));
   packet->SetPayloadType(frame.payload_id);
   packet->SetTimestamp(frame.rtp_timestamp);
diff --git a/modules/rtp_rtcp/source/rtp_sender_audio.h b/modules/rtp_rtcp/source/rtp_sender_audio.h
index 662f908..83a2cb2 100644
--- a/modules/rtp_rtcp/source/rtp_sender_audio.h
+++ b/modules/rtp_rtcp/source/rtp_sender_audio.h
@@ -61,6 +61,9 @@
     // header-extension-for-audio-level-indication.
     // Valid range is [0,127]. Actual value is negative.
     absl::optional<int> audio_level_dbov;
+
+    // Contributing sources list.
+    rtc::ArrayView<const uint32_t> csrcs;
   };
   bool SendAudio(const RtpAudioFrame& frame);
 
diff --git a/modules/rtp_rtcp/source/rtp_sender_audio_unittest.cc b/modules/rtp_rtcp/source/rtp_sender_audio_unittest.cc
index 0db610c..724cd3a 100644
--- a/modules/rtp_rtcp/source/rtp_sender_audio_unittest.cc
+++ b/modules/rtp_rtcp/source/rtp_sender_audio_unittest.cc
@@ -222,4 +222,19 @@
   EXPECT_FALSE(transport_.last_sent_packet().Marker());
 }
 
+TEST_F(RtpSenderAudioTest, SendsCsrcs) {
+  const char payload_name[] = "audio";
+  const uint8_t payload_type = 127;
+  ASSERT_EQ(0, rtp_sender_audio_->RegisterAudioPayload(
+                   payload_name, payload_type, 48000, 0, 1500));
+  uint8_t payload[] = {47, 11, 32, 93, 89};
+
+  std::vector<uint32_t> csrcs({123, 456, 789});
+
+  ASSERT_TRUE(rtp_sender_audio_->SendAudio(
+      {.payload = payload, .payload_id = payload_type, .csrcs = csrcs}));
+
+  EXPECT_EQ(transport_.last_sent_packet().Csrcs(), csrcs);
+}
+
 }  // namespace webrtc