diff --git a/api/frame_transformer_interface.h b/api/frame_transformer_interface.h
index de2c612ac0..5efd3ea051 100644
--- a/api/frame_transformer_interface.h
+++ b/api/frame_transformer_interface.h
@@ -73,6 +73,8 @@ class TransformableAudioFrameInterface : public TransformableFrameInterface {
   // information in the header as needed, for example to compile the list of
   // csrcs.
   virtual const RTPHeader& GetHeader() const = 0;
+
+  virtual rtc::ArrayView<const uint32_t> GetContributingSources() const = 0;
 };
 
 // Objects implement this interface to be notified with the transformed frame.
diff --git a/audio/channel_receive_frame_transformer_delegate.cc b/audio/channel_receive_frame_transformer_delegate.cc
index 0f742e5b16..e8ba6ded47 100644
--- a/audio/channel_receive_frame_transformer_delegate.cc
+++ b/audio/channel_receive_frame_transformer_delegate.cc
@@ -37,6 +37,9 @@ class TransformableIncomingAudioFrame
   uint32_t GetSsrc() const override { return ssrc_; }
   uint32_t GetTimestamp() const override { return header_.timestamp; }
   const RTPHeader& GetHeader() const override { return header_; }
+  rtc::ArrayView<const uint32_t> GetContributingSources() const override {
+    return rtc::ArrayView<const uint32_t>(header_.arrOfCSRCs, header_.numCSRCs);
+  }
   Direction GetDirection() const override { return Direction::kReceiver; }
 
  private: