Request keyframes more frequently on stream start/decoding error.

In this CL:
 - Added FrameObject::is_keyframe() convinience function.
 - Moved logic to request keyframes on decoding error from VideoReceived to
   VideoReceiveStream.
 - Added keyframe_required as a parameter to FrameBuffer::NextFrame.

BUG=webrtc:8074

Review-Url: https://codereview.webrtc.org/2993793002
Cr-Commit-Position: refs/heads/master@{#19280}

webrtc/modules/video_coding/frame_buffer2.cc

@@ -59,7 +59,8 @@ FrameBuffer::~FrameBuffer() {}
 
 FrameBuffer::ReturnReason FrameBuffer::NextFrame(
     int64_t max_wait_time_ms,
-    std::unique_ptr<FrameObject>* frame_out) {
+    std::unique_ptr<FrameObject>* frame_out,
+    bool keyframe_required) {
   TRACE_EVENT0("webrtc", "FrameBuffer::NextFrame");
   int64_t latest_return_time_ms =
       clock_->TimeInMilliseconds() + max_wait_time_ms;
@@ -105,6 +106,10 @@ FrameBuffer::ReturnReason FrameBuffer::NextFrame(
         }
 
         FrameObject* frame = frame_it->second.frame.get();
+
+        if (keyframe_required && !frame->is_keyframe())
+          continue;
+
         next_frame_it_ = frame_it;
         if (frame->RenderTime() == -1)
           frame->SetRenderTime(timing_->RenderTimeMs(frame->timestamp, now_ms));
@@ -272,7 +277,7 @@ int FrameBuffer::InsertFrame(std::unique_ptr<FrameObject> frame) {
   TRACE_EVENT0("webrtc", "FrameBuffer::InsertFrame");
   RTC_DCHECK(frame);
   if (stats_callback_)
-    stats_callback_->OnCompleteFrame(frame->num_references == 0, frame->size());
+    stats_callback_->OnCompleteFrame(frame->is_keyframe(), frame->size());
   FrameKey key(frame->picture_id, frame->spatial_layer);
 
   rtc::CritScope lock(&crit_);
@@ -300,7 +305,7 @@ int FrameBuffer::InsertFrame(std::unique_ptr<FrameObject> frame) {
   if (last_decoded_frame_it_ != frames_.end() &&
       key <= last_decoded_frame_it_->first) {
     if (AheadOf(frame->timestamp, last_decoded_frame_timestamp_) &&
-        frame->num_references == 0) {
+        frame->is_keyframe()) {
       // If this frame has a newer timestamp but an earlier picture id then we
       // assume there has been a jump in the picture id due to some encoder
       // reconfiguration or some other reason. Even though this is not according

webrtc/modules/video_coding/frame_buffer2.h

@@ -57,7 +57,8 @@ class FrameBuffer {
   //    kTimeout.
   //  - If the FrameBuffer is stopped then it will return kStopped.
   ReturnReason NextFrame(int64_t max_wait_time_ms,
-                         std::unique_ptr<FrameObject>* frame_out);
+                         std::unique_ptr<FrameObject>* frame_out,
+                         bool keyframe_required = false);
 
   // Tells the FrameBuffer which protection mode that is in use. Affects
   // the frame timing.

webrtc/modules/video_coding/frame_buffer2_unittest.cc

@@ -167,11 +167,12 @@ class TestFrameBuffer2 : public ::testing::Test {
     return buffer_.InsertFrame(std::move(frame));
   }
 
-  void ExtractFrame(int64_t max_wait_time = 0) {
+  void ExtractFrame(int64_t max_wait_time = 0, bool keyframe_required = false) {
     crit_.Enter();
     if (max_wait_time == 0) {
       std::unique_ptr<FrameObject> frame;
-      FrameBuffer::ReturnReason res = buffer_.NextFrame(0, &frame);
+      FrameBuffer::ReturnReason res =
+          buffer_.NextFrame(0, &frame, keyframe_required);
       if (res != FrameBuffer::ReturnReason::kStopped)
         frames_.emplace_back(std::move(frame));
       crit_.Leave();
@@ -540,5 +541,18 @@ TEST_F(TestFrameBuffer2, InvalidReferences) {
   EXPECT_EQ(2, InsertFrame(2, 0, 3000, false, 1));
 }
 
+TEST_F(TestFrameBuffer2, KeyframeRequired) {
+  EXPECT_EQ(1, InsertFrame(1, 0, 1000, false));
+  EXPECT_EQ(2, InsertFrame(2, 0, 2000, false, 1));
+  EXPECT_EQ(3, InsertFrame(3, 0, 3000, false));
+  ExtractFrame();
+  ExtractFrame(0, true);
+  ExtractFrame();
+
+  CheckFrame(0, 1, 0);
+  CheckFrame(1, 3, 0);
+  CheckNoFrame(2);
+}
+
 }  // namespace video_coding
 }  // namespace webrtc

webrtc/modules/video_coding/frame_object.h

@@ -44,6 +44,8 @@ class FrameObject : public webrtc::VCMEncodedFrame {
 
   size_t size() const { return _length; }
 
+  bool is_keyframe() const { return num_references == 0; }
+
   // The tuple (|picture_id|, |spatial_layer|) uniquely identifies a frame
   // object. For codec types that don't necessarily have picture ids they
   // have to be constructed from the header data relevant to that codec.

webrtc/modules/video_coding/video_receiver.cc

@@ -320,24 +320,7 @@ int32_t VideoReceiver::Decode(const VCMEncodedFrame& frame) {
   if (decoder == nullptr) {
     return VCM_NO_CODEC_REGISTERED;
   }
-  // Decode a frame
-  int32_t ret = decoder->Decode(frame, clock_->TimeInMilliseconds());
-
-  // Check for failed decoding, run frame type request callback if needed.
-  bool request_key_frame = false;
-  if (ret < 0) {
-    request_key_frame = true;
-  }
-
-  if (!frame.Complete() || frame.MissingFrame()) {
-    request_key_frame = true;
-    ret = VCM_OK;
-  }
-  if (request_key_frame) {
-    rtc::CritScope cs(&process_crit_);
-    _scheduleKeyRequest = true;
-  }
-  return ret;
+  return decoder->Decode(frame, clock_->TimeInMilliseconds());
 }
 
 // Register possible receive codecs, can be called multiple times

webrtc/video/video_receive_stream.cc

@@ -491,9 +491,12 @@ void VideoReceiveStream::DecodeThreadFunction(void* ptr) {
 bool VideoReceiveStream::Decode() {
   TRACE_EVENT0("webrtc", "VideoReceiveStream::Decode");
   static const int kMaxWaitForFrameMs = 3000;
+  static const int kMaxWaitForKeyFrameMs = 200;
+
+  int wait_ms = keyframe_required_ ? kMaxWaitForKeyFrameMs : kMaxWaitForFrameMs;
   std::unique_ptr<video_coding::FrameObject> frame;
   video_coding::FrameBuffer::ReturnReason res =
-      frame_buffer_->NextFrame(kMaxWaitForFrameMs, &frame);
+      frame_buffer_->NextFrame(wait_ms, &frame, keyframe_required_);
 
   if (res == video_coding::FrameBuffer::ReturnReason::kStopped) {
     video_receiver_.DecodingStopped();
@@ -502,8 +505,12 @@ bool VideoReceiveStream::Decode() {
 
   if (frame) {
     RTC_DCHECK_EQ(res, video_coding::FrameBuffer::ReturnReason::kFrameFound);
-    if (video_receiver_.Decode(frame.get()) == VCM_OK)
+    if (video_receiver_.Decode(frame.get()) == VCM_OK) {
+      keyframe_required_ = false;
       rtp_video_stream_receiver_.FrameDecoded(frame->picture_id);
+    } else {
+      keyframe_required_ = true;
+    }
   } else {
     RTC_DCHECK_EQ(res, video_coding::FrameBuffer::ReturnReason::kTimeout);
     int64_t now_ms = clock_->TimeInMilliseconds();
@@ -524,7 +531,7 @@ bool VideoReceiveStream::Decode() {
         now_ms - *last_keyframe_packet_ms < kMaxWaitForFrameMs;
 
     if (stream_is_active && !receiving_keyframe) {
-      LOG(LS_WARNING) << "No decodable frame in " << kMaxWaitForFrameMs
+      LOG(LS_WARNING) << "No decodable frame in " << wait_ms
                       << " ms, requesting keyframe.";
       RequestKeyFrame();
     }

webrtc/video/video_receive_stream.h

@@ -144,6 +144,10 @@ class VideoReceiveStream : public webrtc::VideoReceiveStream,
 
   std::unique_ptr<RtpStreamReceiverInterface> media_receiver_;
   std::unique_ptr<RtpStreamReceiverInterface> rtx_receiver_;
+
+  // Whenever we are in an undecodable state (stream has just started or due to
+  // a decoding error) we require a keyframe to restart the stream.
+  bool keyframe_required_ = true;
 };
 }  // namespace internal
 }  // namespace webrtc