Surface the SetMetadata() method so that Chromium can use it.

RTPVideoHeader is changed to non-const to allow modifying it. We want
to do this when implementing setMetadata() in JavaScript or when
refactoring clone() as "construct + set bytes + setMetadata".

Unblocks
https://chromium-review.googlesource.com/c/chromium/src/+/4164979.

Bug: webrtc:14709
Change-Id: I6089df9c03e9aa33feeb0830dd240dd456cb565e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/290981
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39113}

api/frame_transformer_interface.h

@@ -62,6 +62,9 @@ class TransformableVideoFrameInterface : public TransformableFrameInterface {
   virtual std::vector<uint8_t> GetAdditionalData() const = 0;
 
   virtual const VideoFrameMetadata& GetMetadata() const = 0;
+  // TODO(https://crbug.com/webrtc/14709): Make pure virtual when Chromium MOCK
+  // has implemented this.
+  virtual void SetMetadata(const VideoFrameMetadata&) {}
 };
 
 // Extends the TransformableFrameInterface to expose audio-specific information.

api/test/mock_transformable_video_frame.h

@@ -31,6 +31,10 @@ class MockTransformableVideoFrame
               GetMetadata,
               (),
               (const, override));
+  MOCK_METHOD(void,
+              SetMetadata,
+              (const webrtc::VideoFrameMetadata&),
+              (override));
 };
 
 }  // namespace webrtc

modules/rtp_rtcp/source/frame_transformer_factory_unittest.cc

@@ -48,6 +48,10 @@ class MockTransformableVideoFrame
               GetMetadata,
               (),
               (const, override));
+  MOCK_METHOD(void,
+              SetMetadata,
+              (const webrtc::VideoFrameMetadata&),
+              (override));
 };
 
 TEST(FrameTransformerFactory, CloneVideoFrame) {

modules/rtp_rtcp/source/rtp_sender_video_frame_transformer_delegate.cc

@@ -69,6 +69,12 @@ class TransformableVideoSenderFrame : public TransformableVideoFrameInterface {
   }
 
   const VideoFrameMetadata& GetMetadata() const override { return metadata_; }
+  void SetMetadata(const VideoFrameMetadata& metadata) override {
+    header_.SetFromMetadata(metadata);
+    // We have to keep a local copy because GetMetadata() has to return a
+    // reference.
+    metadata_ = header_.GetAsMetadata();
+  }
 
   const RTPVideoHeader& GetHeader() const { return header_; }
   uint8_t GetPayloadType() const override { return payload_type_; }
@@ -83,8 +89,12 @@ class TransformableVideoSenderFrame : public TransformableVideoFrameInterface {
 
  private:
   rtc::scoped_refptr<EncodedImageBufferInterface> encoded_data_;
-  const RTPVideoHeader header_;
-  const VideoFrameMetadata metadata_;
+  RTPVideoHeader header_;
+  // This is a copy of `header_.GetAsMetadata()`, only needed because the
+  // interface says GetMetadata() must return a const ref rather than a value.
+  // TODO(crbug.com/webrtc/14709): Change the interface and delete this variable
+  // to reduce risk of it getting out-of-sync with `header_.GetAsMetadata()`.
+  VideoFrameMetadata metadata_;
   const VideoFrameType frame_type_;
   const uint8_t payload_type_;
   const absl::optional<VideoCodecType> codec_type_ = absl::nullopt;

video/rtp_video_stream_receiver_frame_transformer_delegate.cc

@@ -15,6 +15,7 @@
 
 #include "absl/memory/memory.h"
 #include "modules/rtp_rtcp/source/rtp_descriptor_authentication.h"
+#include "rtc_base/checks.h"
 #include "rtc_base/thread.h"
 
 namespace webrtc {
@@ -53,6 +54,10 @@ class TransformableVideoReceiverFrame
   }
 
   const VideoFrameMetadata& GetMetadata() const override { return metadata_; }
+  void SetMetadata(const VideoFrameMetadata&) override {
+    RTC_DCHECK_NOTREACHED()
+        << "TransformableVideoReceiverFrame::SetMetadata is not implemented";
+  }
 
   std::unique_ptr<RtpFrameObject> ExtractFrame() && {
     return std::move(frame_);