Fix bug where min transmit bitrate wasn't working

A recent refactoring (r13192) introduced a bug where the min transmit
config wasn't being respected. Specifically, if a VideoSendStream was
created without it and the reconfigured, the min transmit bitrate would
not take effect. Probably the other way around as well.

BUG=webrtc::5687

Review-Url: https://codereview.webrtc.org/2106183002
Cr-Commit-Position: refs/heads/master@{#13390}

webrtc/call.h

@@ -92,8 +92,9 @@ class Call {
   };
 
   struct Stats {
-    int send_bandwidth_bps = 0;
-    int recv_bandwidth_bps = 0;
+    int send_bandwidth_bps = 0;       // Estimated available send bandwidth.
+    int max_padding_bitrate_bps = 0;  // Cumulative configured max padding.
+    int recv_bandwidth_bps = 0;       // Estimated available receive bandwidth.
     int64_t pacer_delay_ms = 0;
     int64_t rtt_ms = -1;
   };

webrtc/call/call.cc

@@ -189,6 +189,7 @@ class Call : public webrtc::Call,
   int64_t pacer_bitrate_sum_kbits_ GUARDED_BY(&bitrate_crit_);
   uint32_t min_allocated_send_bitrate_bps_ GUARDED_BY(&bitrate_crit_);
   int64_t num_bitrate_updates_ GUARDED_BY(&bitrate_crit_);
+  uint32_t configured_max_padding_bitrate_bps_ GUARDED_BY(&bitrate_crit_);
 
   std::map<std::string, rtc::NetworkRoute> network_routes_;
 
@@ -229,6 +230,8 @@ Call::Call(const Call::Config& config)
       pacer_bitrate_sum_kbits_(0),
       min_allocated_send_bitrate_bps_(0),
       num_bitrate_updates_(0),
+      configured_max_padding_bitrate_bps_(0),
+
       remb_(clock_),
       congestion_controller_(
           new CongestionController(clock_, this, &remb_, event_log_.get())),
@@ -552,6 +555,10 @@ Call::Stats Call::GetStats() const {
   stats.recv_bandwidth_bps = recv_bandwidth;
   stats.pacer_delay_ms = congestion_controller_->GetPacerQueuingDelayMs();
   stats.rtt_ms = call_stats_->rtcp_rtt_stats()->LastProcessedRtt();
+  {
+    rtc::CritScope cs(&bitrate_crit_);
+    stats.max_padding_bitrate_bps = configured_max_padding_bitrate_bps_;
+  }
   return stats;
 }
 
@@ -714,6 +721,7 @@ void Call::OnAllocationLimitsChanged(uint32_t min_send_bitrate_bps,
       min_send_bitrate_bps, max_padding_bitrate_bps);
   rtc::CritScope lock(&bitrate_crit_);
   min_allocated_send_bitrate_bps_ = min_send_bitrate_bps;
+  configured_max_padding_bitrate_bps_ = max_padding_bitrate_bps;
 }
 
 void Call::ConfigureSync(const std::string& sync_group) {

webrtc/video/video_send_stream.cc

@@ -589,6 +589,16 @@ void VideoSendStream::EncoderProcess() {
       current_encoder_settings_->video_codec.startBitrate = std::max(
           bitrate_allocator_->GetStartBitrate(this) / 1000,
           static_cast<int>(current_encoder_settings_->video_codec.minBitrate));
+
+      if (state_ == State::kStarted) {
+        bitrate_allocator_->AddObserver(
+            this, current_encoder_settings_->video_codec.minBitrate * 1000,
+            current_encoder_settings_->video_codec.maxBitrate * 1000,
+            CalulcateMaxPadBitrateBps(current_encoder_settings_->config,
+                                      config_.suspend_below_min_bitrate),
+            !config_.suspend_below_min_bitrate);
+      }
+
       payload_router_.SetSendStreams(current_encoder_settings_->config.streams);
       vie_encoder_.SetEncoder(current_encoder_settings_->video_codec,
                               payload_router_.MaxPayloadLength());

webrtc/video/video_send_stream_tests.cc

@@ -1121,6 +1121,97 @@ TEST_F(VideoSendStreamTest, MinTransmitBitrateRespectsRemb) {
   RunBaseTest(&test);
 }
 
+class MaxPaddingSetTest : public test::SendTest {
+ public:
+  static const uint32_t kMinTransmitBitrateBps = 400000;
+  static const uint32_t kActualEncodeBitrateBps = 40000;
+  static const uint32_t kMinPacketsToSend = 50;
+
+  explicit MaxPaddingSetTest(bool test_switch_content_type)
+      : SendTest(test::CallTest::kDefaultTimeoutMs),
+        call_(nullptr),
+        send_stream_(nullptr),
+        packets_sent_(0),
+        running_without_padding_(test_switch_content_type) {}
+
+  void OnVideoStreamsCreated(
+      VideoSendStream* send_stream,
+      const std::vector<VideoReceiveStream*>& receive_streams) override {
+    send_stream_ = send_stream;
+  }
+
+  void ModifyVideoConfigs(
+      VideoSendStream::Config* send_config,
+      std::vector<VideoReceiveStream::Config>* receive_configs,
+      VideoEncoderConfig* encoder_config) override {
+    RTC_DCHECK_EQ(1u, encoder_config->streams.size());
+    if (running_without_padding_) {
+      encoder_config->min_transmit_bitrate_bps = 0;
+      encoder_config->content_type =
+          VideoEncoderConfig::ContentType::kRealtimeVideo;
+    } else {
+      encoder_config->min_transmit_bitrate_bps = kMinTransmitBitrateBps;
+      encoder_config->content_type = VideoEncoderConfig::ContentType::kScreen;
+    }
+    encoder_config_ = *encoder_config;
+  }
+
+  void OnCallsCreated(Call* sender_call, Call* receiver_call) override {
+    call_ = sender_call;
+  }
+
+  Action OnSendRtp(const uint8_t* packet, size_t length) override {
+    rtc::CritScope lock(&crit_);
+
+    if (running_without_padding_)
+      EXPECT_EQ(0, call_->GetStats().max_padding_bitrate_bps);
+
+    // Wait until at least kMinPacketsToSend frames have been encoded, so that
+    // we have reliable data.
+    if (++packets_sent_ < kMinPacketsToSend)
+      return SEND_PACKET;
+
+    if (running_without_padding_) {
+      // We've sent kMinPacketsToSend packets with default configuration, switch
+      // to enabling screen content and setting min transmit bitrate.
+      packets_sent_ = 0;
+      encoder_config_.min_transmit_bitrate_bps = kMinTransmitBitrateBps;
+      encoder_config_.content_type = VideoEncoderConfig::ContentType::kScreen;
+      send_stream_->ReconfigureVideoEncoder(encoder_config_);
+      running_without_padding_ = false;
+      return SEND_PACKET;
+    }
+
+    // Make sure the pacer has been configured with a min transmit bitrate.
+    if (call_->GetStats().max_padding_bitrate_bps > 0)
+      observation_complete_.Set();
+
+    return SEND_PACKET;
+  }
+
+  void PerformTest() override {
+    ASSERT_TRUE(Wait()) << "Timed out waiting for a valid padding bitrate.";
+  }
+
+ private:
+  rtc::CriticalSection crit_;
+  Call* call_;
+  VideoSendStream* send_stream_;
+  VideoEncoderConfig encoder_config_;
+  uint32_t packets_sent_ GUARDED_BY(crit_);
+  bool running_without_padding_;
+};
+
+TEST_F(VideoSendStreamTest, RespectsMinTransmitBitrate) {
+  MaxPaddingSetTest test(false);
+  RunBaseTest(&test);
+}
+
+TEST_F(VideoSendStreamTest, RespectsMinTransmitBitrateAfterContentSwitch) {
+  MaxPaddingSetTest test(true);
+  RunBaseTest(&test);
+}
+
 TEST_F(VideoSendStreamTest, CanReconfigureToUseStartBitrateAbovePreviousMax) {
   class StartBitrateObserver : public test::FakeEncoder {
    public: