Don't recreate the VideoReceiveStream on SetFrameDecryptor in the MediaEngine.

This change introduces new logic to allow the injection of the FrameDecryptor
into an arbitrary already running VideoReceiveStream without resetting it. It
does this by taking advantage of the BufferedFrameDecryptor which will
forcefully be created regardless of whether a FrameDecryptor is passed in
during construction of the VideoReceiver if the
crypto_option.require_frame_encryption is true. By allowing the
BufferedFrameDecryptor to swap out which FrameDecryptor it uses this allows the
Receiver to switch decryptors without resetting the stream.

This is intended to mostly be used when you set your FrameDecryptor at a point
post creation for the first time.

Bug: webrtc:10416
Change-Id: If656b2acc447e2e77537cfa394729e5c3a8b660a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130361
Commit-Queue: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27458}

call/call.cc

@@ -404,8 +404,6 @@ class Call final : public webrtc::Call,
   MediaTransportInterface* media_transport_
       RTC_GUARDED_BY(&target_observer_crit_) = nullptr;
 
-  const bool field_trial_webrtc_video_buffer_packets_with_unknown_ssrc_;
-
   RTC_DISALLOW_COPY_AND_ASSIGN(Call);
 };
 }  // namespace internal
@@ -488,10 +486,7 @@ Call::Call(Clock* clock,
       receive_side_cc_(clock_, transport_send->packet_router()),
       receive_time_calculator_(ReceiveTimeCalculator::CreateFromFieldTrial()),
       video_send_delay_stats_(new SendDelayStats(clock_)),
-      start_ms_(clock_->TimeInMilliseconds()),
-      field_trial_webrtc_video_buffer_packets_with_unknown_ssrc_(
-          webrtc::field_trial::IsEnabled(
-              "WebRTC-Video-BufferPacketsWithUnknownSsrc")) {
+      start_ms_(clock_->TimeInMilliseconds()) {
   RTC_DCHECK(config.event_log != nullptr);
   transport_send_ = std::move(transport_send);
   transport_send_ptr_ = transport_send_.get();
@@ -1416,27 +1411,6 @@ PacketReceiver::DeliveryStatus Call::DeliverRtp(MediaType media_type,
     return DELIVERY_UNKNOWN_SSRC;
   }
 
-  if (field_trial_webrtc_video_buffer_packets_with_unknown_ssrc_) {
-    // Check if packet arrives for a stream that requires decryption
-    // but does not yet have a FrameDecryptor.
-    // In that case buffer the packet and replay it when the frame decryptor
-    // is set.
-    // TODO(bugs.webrtc.org/10416) : Remove this check once FrameDecryptor
-    // is created as part of creating receive stream.
-    const uint32_t ssrc = parsed_packet.Ssrc();
-    auto vrs = std::find_if(
-        video_receive_streams_.begin(), video_receive_streams_.end(),
-        [&](const VideoReceiveStream* stream) {
-          return (stream->config().rtp.remote_ssrc == ssrc ||
-                  stream->config().rtp.rtx_ssrc == ssrc);
-        });
-    if (vrs != video_receive_streams_.end() &&
-        (*vrs)->config().crypto_options.sframe.require_frame_encryption &&
-        (*vrs)->config().frame_decryptor == nullptr) {
-      return DELIVERY_UNKNOWN_SSRC;
-    }
-  }
-
   parsed_packet.IdentifyExtensions(it->second.extensions);
 
   NotifyBweOfReceivedPacket(parsed_packet, media_type);

call/video_receive_stream.h

@@ -260,6 +260,11 @@ class VideoReceiveStream {
   // Returns current value of base minimum delay in milliseconds.
   virtual int GetBaseMinimumPlayoutDelayMs() const = 0;
 
+  // Allows a FrameDecryptor to be attached to a VideoReceiveStream after
+  // creation without resetting the decoder state.
+  virtual void SetFrameDecryptor(
+      rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor) = 0;
+
  protected:
   virtual ~VideoReceiveStream() {}
 };

media/engine/fake_webrtc_call.h

@@ -226,6 +226,9 @@ class FakeVideoReceiveStream final : public webrtc::VideoReceiveStream {
     return base_mininum_playout_delay_ms_;
   }
 
+  void SetFrameDecryptor(rtc::scoped_refptr<webrtc::FrameDecryptorInterface>
+                             frame_decryptor) override {}
+
  private:
   // webrtc::VideoReceiveStream implementation.
   void Start() override;

media/engine/webrtc_video_engine.cc

@@ -2538,12 +2538,7 @@ void WebRtcVideoChannel::WebRtcVideoReceiveStream::RecreateWebRtcVideoStream() {
 
   if (webrtc::field_trial::IsEnabled(
           "WebRTC-Video-BufferPacketsWithUnknownSsrc")) {
-    // TODO(bugs.webrtc.org/10416) : Remove this check and backfill
-    // when the stream is created (i.e remote check for frame_decryptor)
-    // once FrameDecryptor is created as part of creating receive stream.
-    if (config_.frame_decryptor) {
-      channel_->BackfillBufferedPackets(stream_params_.ssrcs);
-    }
+    channel_->BackfillBufferedPackets(stream_params_.ssrcs);
   }
 }
 
@@ -2602,9 +2597,9 @@ void WebRtcVideoChannel::WebRtcVideoReceiveStream::SetFrameDecryptor(
   config_.frame_decryptor = frame_decryptor;
   if (stream_) {
     RTC_LOG(LS_INFO)
-        << "RecreateWebRtcStream (recv) because of SetFrameDecryptor, "
+        << "Setting FrameDecryptor (recv) because of SetFrameDecryptor, "
         << "remote_ssrc=" << config_.rtp.remote_ssrc;
-    RecreateWebRtcVideoStream();
+    stream_->SetFrameDecryptor(frame_decryptor);
   }
 }
 

video/buffered_frame_decryptor.cc

@@ -20,21 +20,25 @@ namespace webrtc {
 
 BufferedFrameDecryptor::BufferedFrameDecryptor(
     OnDecryptedFrameCallback* decrypted_frame_callback,
-    OnDecryptionStatusChangeCallback* decryption_status_change_callback,
-    rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor)
+    OnDecryptionStatusChangeCallback* decryption_status_change_callback)
     : generic_descriptor_auth_experiment_(
           field_trial::IsEnabled("WebRTC-GenericDescriptorAuth")),
-      frame_decryptor_(std::move(frame_decryptor)),
       decrypted_frame_callback_(decrypted_frame_callback),
       decryption_status_change_callback_(decryption_status_change_callback) {}
 
 BufferedFrameDecryptor::~BufferedFrameDecryptor() {}
 
+void BufferedFrameDecryptor::SetFrameDecryptor(
+    rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor) {
+  frame_decryptor_ = std::move(frame_decryptor);
+}
+
 void BufferedFrameDecryptor::ManageEncryptedFrame(
     std::unique_ptr<video_coding::RtpFrameObject> encrypted_frame) {
   switch (DecryptFrame(encrypted_frame.get())) {
     case FrameDecision::kStash:
       if (stashed_frames_.size() >= kMaxStashedFrames) {
+        RTC_LOG(LS_WARNING) << "Encrypted frame stash full poping oldest item.";
         stashed_frames_.pop_front();
       }
       stashed_frames_.push_back(std::move(encrypted_frame));
@@ -52,9 +56,9 @@ BufferedFrameDecryptor::FrameDecision BufferedFrameDecryptor::DecryptFrame(
     video_coding::RtpFrameObject* frame) {
   // Optionally attempt to decrypt the raw video frame if it was provided.
   if (frame_decryptor_ == nullptr) {
-    RTC_LOG(LS_WARNING) << "Frame decryption required but not attached to this "
-                           "stream. Dropping frame.";
-    return FrameDecision::kDrop;
+    RTC_LOG(LS_INFO) << "Frame decryption required but not attached to this "
+                        "stream. Stashing frame.";
+    return FrameDecision::kStash;
   }
   // When using encryption we expect the frame to have the generic descriptor.
   absl::optional<RtpGenericFrameDescriptor> descriptor =

video/buffered_frame_decryptor.h

@@ -58,12 +58,18 @@ class BufferedFrameDecryptor final {
   // Constructs a new BufferedFrameDecryptor that can hold
   explicit BufferedFrameDecryptor(
       OnDecryptedFrameCallback* decrypted_frame_callback,
-      OnDecryptionStatusChangeCallback* decryption_status_change_callback,
-      rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor);
+      OnDecryptionStatusChangeCallback* decryption_status_change_callback);
   ~BufferedFrameDecryptor();
   // This object cannot be copied.
   BufferedFrameDecryptor(const BufferedFrameDecryptor&) = delete;
   BufferedFrameDecryptor& operator=(const BufferedFrameDecryptor&) = delete;
+
+  // Sets a new frame decryptor as the decryptor for the buffered frame
+  // decryptor. This allows the decryptor to be switched out without resetting
+  // the video stream.
+  void SetFrameDecryptor(
+      rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor);
+
   // Determines whether the frame should be stashed, dropped or handed off to
   // the OnDecryptedFrameCallback.
   void ManageEncryptedFrame(
@@ -86,7 +92,7 @@ class BufferedFrameDecryptor final {
   const bool generic_descriptor_auth_experiment_;
   bool first_frame_decrypted_ = false;
   int last_status_ = -1;
-  const rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor_;
+  rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor_;
   OnDecryptedFrameCallback* const decrypted_frame_callback_;
   OnDecryptionStatusChangeCallback* const decryption_status_change_callback_;
   std::deque<std::unique_ptr<video_coding::RtpFrameObject>> stashed_frames_;

video/buffered_frame_decryptor_unittest.cc

@@ -107,8 +107,9 @@ class BufferedFrameDecryptorTest
     decryption_status_change_count_ = 0;
     seq_num_ = 0;
     mock_frame_decryptor_ = new rtc::RefCountedObject<MockFrameDecryptor>();
-    buffered_frame_decryptor_ = absl::make_unique<BufferedFrameDecryptor>(
-        this, this, mock_frame_decryptor_.get());
+    buffered_frame_decryptor_ =
+        absl::make_unique<BufferedFrameDecryptor>(this, this);
+    buffered_frame_decryptor_->SetFrameDecryptor(mock_frame_decryptor_.get());
   }
 
   static const size_t kMaxStashedFrames;
@@ -220,4 +221,26 @@ TEST_F(BufferedFrameDecryptorTest, MaximumNumberOfFramesStored) {
   EXPECT_EQ(decryption_status_change_count_, static_cast<size_t>(2));
 }
 
+// Verifies if a BufferedFrameDecryptor is attached but has no FrameDecryptor
+// attached it will still store frames up to the frame max.
+TEST_F(BufferedFrameDecryptorTest, FramesStoredIfDecryptorNull) {
+  buffered_frame_decryptor_->SetFrameDecryptor(nullptr);
+  for (size_t i = 0; i < (2 * kMaxStashedFrames); ++i) {
+    buffered_frame_decryptor_->ManageEncryptedFrame(CreateRtpFrameObject(true));
+  }
+
+  EXPECT_CALL(*mock_frame_decryptor_, Decrypt)
+      .Times(kMaxStashedFrames + 1)
+      .WillRepeatedly(Return(0));
+  EXPECT_CALL(*mock_frame_decryptor_, GetMaxPlaintextByteSize)
+      .WillRepeatedly(Return(0));
+
+  // Attach the frame decryptor at a later point after frames have arrived.
+  buffered_frame_decryptor_->SetFrameDecryptor(mock_frame_decryptor_.get());
+
+  // Next frame should trigger kMaxStashedFrame decryptions.
+  buffered_frame_decryptor_->ManageEncryptedFrame(CreateRtpFrameObject(true));
+  EXPECT_EQ(decrypted_frame_call_count_, kMaxStashedFrames + 1);
+}
+
 }  // namespace webrtc

video/rtp_video_stream_receiver.cc

@@ -175,11 +175,14 @@ RtpVideoStreamReceiver::RtpVideoStreamReceiver(
       clock_, kPacketBufferStartSize, packet_buffer_max_size, this);
   reference_finder_ =
       absl::make_unique<video_coding::RtpFrameReferenceFinder>(this);
+
   // Only construct the encrypted receiver if frame encryption is enabled.
-  if (frame_decryptor != nullptr ||
-      config_.crypto_options.sframe.require_frame_encryption) {
+  if (config_.crypto_options.sframe.require_frame_encryption) {
     buffered_frame_decryptor_ =
-        absl::make_unique<BufferedFrameDecryptor>(this, this, frame_decryptor);
+        absl::make_unique<BufferedFrameDecryptor>(this, this);
+    if (frame_decryptor != nullptr) {
+      buffered_frame_decryptor_->SetFrameDecryptor(std::move(frame_decryptor));
+    }
   }
 }
 
@@ -452,6 +455,16 @@ void RtpVideoStreamReceiver::OnDecryptionStatusChange(int status) {
   frames_decryptable_.store(status == 0);
 }
 
+void RtpVideoStreamReceiver::SetFrameDecryptor(
+    rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor) {
+  RTC_DCHECK_RUN_ON(&network_tc_);
+  if (buffered_frame_decryptor_ == nullptr) {
+    buffered_frame_decryptor_ =
+        absl::make_unique<BufferedFrameDecryptor>(this, this);
+  }
+  buffered_frame_decryptor_->SetFrameDecryptor(std::move(frame_decryptor));
+}
+
 void RtpVideoStreamReceiver::UpdateRtt(int64_t max_rtt_ms) {
   if (nack_module_)
     nack_module_->UpdateRtt(max_rtt_ms);

video/rtp_video_stream_receiver.h

@@ -155,6 +155,11 @@ class RtpVideoStreamReceiver : public LossNotificationSender,
   // Implements OnDecryptionStatusChangeCallback.
   void OnDecryptionStatusChange(int status) override;
 
+  // Optionally set a frame decryptor after a stream has started. This will not
+  // reset the decoder state.
+  void SetFrameDecryptor(
+      rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor);
+
   // Called by VideoReceiveStream when stats are updated.
   void UpdateRtt(int64_t max_rtt_ms);
 

video/video_receive_stream.cc

@@ -479,6 +479,11 @@ void VideoReceiveStream::OnFrame(const VideoFrame& video_frame) {
   stats_proxy_.OnRenderedFrame(video_frame);
 }
 
+void VideoReceiveStream::SetFrameDecryptor(
+    rtc::scoped_refptr<webrtc::FrameDecryptorInterface> frame_decryptor) {
+  rtp_video_stream_receiver_.SetFrameDecryptor(std::move(frame_decryptor));
+}
+
 void VideoReceiveStream::SendNack(
     const std::vector<uint16_t>& sequence_numbers) {
   rtp_video_stream_receiver_.RequestPacketRetransmit(sequence_numbers);

video/video_receive_stream.h

@@ -94,6 +94,9 @@ class VideoReceiveStream : public webrtc::VideoReceiveStream,
   bool SetBaseMinimumPlayoutDelayMs(int delay_ms) override;
   int GetBaseMinimumPlayoutDelayMs() const override;
 
+  void SetFrameDecryptor(
+      rtc::scoped_refptr<FrameDecryptorInterface> frame_decryptor) override;
+
   // Implements rtc::VideoSinkInterface<VideoFrame>.
   void OnFrame(const VideoFrame& video_frame) override;