diff --git a/api/frame_transformer_interface.h b/api/frame_transformer_interface.h
index 5bbcffe28e..102ac33334 100644
--- a/api/frame_transformer_interface.h
+++ b/api/frame_transformer_interface.h
@@ -73,11 +73,7 @@ class TransformableAudioFrameInterface : public TransformableFrameInterface {
 
   virtual rtc::ArrayView<const uint32_t> GetContributingSources() const = 0;
 
-  // TODO(crbug.com/1453226): Change this to pure virtual after it
-  // is implemented everywhere.
-  virtual const absl::optional<uint16_t> SequenceNumber() const {
-    return absl::nullopt;
-  }
+  virtual const absl::optional<uint16_t> SequenceNumber() const = 0;
 
   virtual absl::optional<uint64_t> AbsoluteCaptureTimestamp() const = 0;
 
diff --git a/audio/channel_send_frame_transformer_delegate.cc b/audio/channel_send_frame_transformer_delegate.cc
index ac32410aed..6d3c011862 100644
--- a/audio/channel_send_frame_transformer_delegate.cc
+++ b/audio/channel_send_frame_transformer_delegate.cc
@@ -58,7 +58,8 @@ class TransformableOutgoingAudioFrame
       absl::optional<uint64_t> absolute_capture_timestamp_ms,
       uint32_t ssrc,
       std::vector<uint32_t> csrcs,
-      const std::string& codec_mime_type)
+      const std::string& codec_mime_type,
+      absl::optional<uint16_t> sequence_number)
       : frame_type_(frame_type),
         payload_type_(payload_type),
         rtp_timestamp_with_offset_(rtp_timestamp_with_offset),
@@ -66,7 +67,8 @@ class TransformableOutgoingAudioFrame
         absolute_capture_timestamp_ms_(absolute_capture_timestamp_ms),
         ssrc_(ssrc),
         csrcs_(std::move(csrcs)),
-        codec_mime_type_(codec_mime_type) {}
+        codec_mime_type_(codec_mime_type),
+        sequence_number_(sequence_number) {}
   ~TransformableOutgoingAudioFrame() override = default;
   rtc::ArrayView<const uint8_t> GetData() const override { return payload_; }
   void SetData(rtc::ArrayView<const uint8_t> data) override {
@@ -88,7 +90,7 @@ class TransformableOutgoingAudioFrame
   }
 
   const absl::optional<uint16_t> SequenceNumber() const override {
-    return absl::nullopt;
+    return sequence_number_;
   }
 
   void SetRTPTimestamp(uint32_t rtp_timestamp_with_offset) override {
@@ -108,6 +110,7 @@ class TransformableOutgoingAudioFrame
   uint32_t ssrc_;
   std::vector<uint32_t> csrcs_;
   std::string codec_mime_type_;
+  absl::optional<uint16_t> sequence_number_;
 };
 }  // namespace
 
@@ -155,7 +158,8 @@ void ChannelSendFrameTransformerDelegate::Transform(
       std::make_unique<TransformableOutgoingAudioFrame>(
           frame_type, payload_type, rtp_timestamp, payload_data, payload_size,
           absolute_capture_timestamp_ms, ssrc,
-          /*csrcs=*/std::vector<uint32_t>(), codec_mimetype));
+          /*csrcs=*/std::vector<uint32_t>(), codec_mimetype,
+          /*sequence_number=*/absl::nullopt));
 }
 
 void ChannelSendFrameTransformerDelegate::OnTransformedFrame(
@@ -203,7 +207,7 @@ std::unique_ptr<TransformableAudioFrameInterface> CloneSenderAudioFrame(
       original->GetPayloadType(), original->GetTimestamp(),
       original->GetData().data(), original->GetData().size(),
       original->AbsoluteCaptureTimestamp(), original->GetSsrc(),
-      std::move(csrcs), original->GetMimeType());
+      std::move(csrcs), original->GetMimeType(), original->SequenceNumber());
 }
 
 }  // namespace webrtc
diff --git a/audio/channel_send_frame_transformer_delegate_unittest.cc b/audio/channel_send_frame_transformer_delegate_unittest.cc
index 5295e2657f..428235efc9 100644
--- a/audio/channel_send_frame_transformer_delegate_unittest.cc
+++ b/audio/channel_send_frame_transformer_delegate_unittest.cc
@@ -68,6 +68,7 @@ std::unique_ptr<TransformableAudioFrameInterface> CreateMockReceiverFrame(
   ON_CALL(*mock_frame, GetDirection)
       .WillByDefault(Return(TransformableFrameInterface::Direction::kReceiver));
   ON_CALL(*mock_frame, GetContributingSources).WillByDefault(Return(csrcs));
+  ON_CALL(*mock_frame, SequenceNumber).WillByDefault(Return(987654321));
   return mock_frame;
 }
 
@@ -252,6 +253,7 @@ TEST(ChannelSendFrameTransformerDelegateTest, CloningReceiverFrameWithCsrcs) {
   ASSERT_NE(frame->GetContributingSources().size(), 0u);
   EXPECT_THAT(cloned_frame->GetContributingSources(),
               ElementsAreArray(frame->GetContributingSources()));
+  EXPECT_EQ(cloned_frame->SequenceNumber(), frame->SequenceNumber());
 }
 
 }  // namespace