Implement minimum transmit bitrate.

Utilizing minimum transmission bitrate prevents low remote bitrate
estimates (bitrate estimation dips) when encoding non-complex content
such as screenshare of a static image even though there's nothing wrong
with the link.

Requires pacing to be enabled for now, pending issue 3036.

BUG=3014
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/9719004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5694 4adac7df-926f-26a2-2b94-8c16560cd09d

3 files changed, 25 insertions, 16 deletions

diff --git a/test/fake_encoder.cc b/test/fake_encoder.cc
index f4e5227e..fc8712e5 100644
--- a/test/fake_encoder.cc
+++ b/test/fake_encoder.cc
@@ -19,6 +19,7 @@ FakeEncoder::FakeEncoder(Clock* clock)
     : clock_(clock),
       callback_(NULL),
       target_bitrate_kbps_(0),
+      max_target_bitrate_kbps_(-1),
       last_encode_time_ms_(0) {
   // Generate some arbitrary not-all-zero data
   for (size_t i = 0; i < sizeof(encoded_buffer_); ++i) {
@@ -62,6 +63,11 @@ void FakeEncoder::SetCodecSettings(VideoCodec* codec,
   strcpy(codec->plName, "FAKE");
 }
 
+void FakeEncoder::SetMaxBitrate(int max_kbps) {
+  assert(max_kbps >= -1);  // max_kbps == -1 disables it.
+  max_target_bitrate_kbps_ = max_kbps;
+}
+
 int32_t FakeEncoder::InitEncode(const VideoCodec* config,
                                 int32_t number_of_cores,
                                 uint32_t max_payload_size) {
@@ -75,19 +81,22 @@ int32_t FakeEncoder::Encode(
     const CodecSpecificInfo* codec_specific_info,
     const std::vector<VideoFrameType>* frame_types) {
   assert(config_.maxFramerate > 0);
-  int delta_since_last_encode = 1000 / config_.maxFramerate;
+  int time_since_last_encode_ms = 1000 / config_.maxFramerate;
   int64_t time_now_ms = clock_->TimeInMilliseconds();
   if (last_encode_time_ms_ > 0) {
     // For all frames but the first we can estimate the display time by looking
     // at the display time of the previous frame.
-    delta_since_last_encode = time_now_ms - last_encode_time_ms_;
+    time_since_last_encode_ms = time_now_ms - last_encode_time_ms_;
   }
 
-  int bits_available = target_bitrate_kbps_ * delta_since_last_encode;
+  int bits_available = target_bitrate_kbps_ * time_since_last_encode_ms;
   int min_bits =
-      config_.simulcastStream[0].minBitrate * delta_since_last_encode;
+      config_.simulcastStream[0].minBitrate * time_since_last_encode_ms;
   if (bits_available < min_bits)
     bits_available = min_bits;
+  int max_bits = max_target_bitrate_kbps_ * time_since_last_encode_ms;
+  if (max_bits > 0 && max_bits < bits_available)
+    bits_available = max_bits;
   last_encode_time_ms_ = time_now_ms;
 
   for (int i = 0; i < config_.numberOfSimulcastStreams; ++i) {
@@ -95,10 +104,10 @@ int32_t FakeEncoder::Encode(
     memset(&specifics, 0, sizeof(specifics));
     specifics.codecType = kVideoCodecGeneric;
     specifics.codecSpecific.generic.simulcast_idx = i;
-    int min_stream_bits = config_.simulcastStream[i].minBitrate *
-        delta_since_last_encode;
-    int max_stream_bits = config_.simulcastStream[i].maxBitrate *
-        delta_since_last_encode;
+    int min_stream_bits =
+        config_.simulcastStream[i].minBitrate * time_since_last_encode_ms;
+    int max_stream_bits =
+        config_.simulcastStream[i].maxBitrate * time_since_last_encode_ms;
     int stream_bits = (bits_available > max_stream_bits) ? max_stream_bits :
         bits_available;
     int stream_bytes = (stream_bits + 7) / 8;
@@ -110,7 +119,8 @@ int32_t FakeEncoder::Encode(
     encoded._timeStamp = input_image.timestamp();
     encoded.capture_time_ms_ = input_image.render_time_ms();
     encoded._frameType = (*frame_types)[i];
-    if (min_stream_bits > bits_available) {
+    // Always encode something on the first frame.
+    if (min_stream_bits > bits_available && i > 0) {
       encoded._length = 0;
       encoded._frameType = kSkipFrame;
     }
@@ -138,5 +148,6 @@ int32_t FakeEncoder::SetRates(uint32_t new_target_bitrate, uint32_t framerate) {
   target_bitrate_kbps_ = new_target_bitrate;
   return 0;
 }
+
 }  // namespace test
 }  // namespace webrtc
diff --git a/test/fake_encoder.h b/test/fake_encoder.h
index c57a4dce..e2d8d6b4 100644
--- a/test/fake_encoder.h
+++ b/test/fake_encoder.h
@@ -25,23 +25,20 @@ class FakeEncoder : public VideoEncoder {
   virtual ~FakeEncoder();
 
   static void SetCodecSettings(VideoCodec* codec, size_t num_streams);
+  // Sets max bitrate. Not thread-safe, call before registering the encoder.
+  void SetMaxBitrate(int max_kbps);
 
   virtual int32_t InitEncode(const VideoCodec* config,
                              int32_t number_of_cores,
                              uint32_t max_payload_size) OVERRIDE;
-
   virtual int32_t Encode(
      const I420VideoFrame& input_image,
      const CodecSpecificInfo* codec_specific_info,
      const std::vector<VideoFrameType>* frame_types) OVERRIDE;
-
   virtual int32_t RegisterEncodeCompleteCallback(
       EncodedImageCallback* callback) OVERRIDE;
-
   virtual int32_t Release() OVERRIDE;
-
   virtual int32_t SetChannelParameters(uint32_t packet_loss, int rtt) OVERRIDE;
-
   virtual int32_t SetRates(uint32_t new_target_bitrate,
                            uint32_t framerate) OVERRIDE;
 
@@ -50,6 +47,7 @@ class FakeEncoder : public VideoEncoder {
   VideoCodec config_;
   EncodedImageCallback* callback_;
   int target_bitrate_kbps_;
+  int max_target_bitrate_kbps_;
   int64_t last_encode_time_ms_;
   uint8_t encoded_buffer_[100000];
 };
diff --git a/test/rtp_rtcp_observer.h b/test/rtp_rtcp_observer.h
index 5ed9a3f3..00422cce 100644
--- a/test/rtp_rtcp_observer.h
+++ b/test/rtp_rtcp_observer.h
@@ -33,8 +33,8 @@ class RtpRtcpObserver {
     return &receive_transport_;
   }
 
-  void SetReceivers(PacketReceiver* send_transport_receiver,
-                    PacketReceiver* receive_transport_receiver) {
+  virtual void SetReceivers(PacketReceiver* send_transport_receiver,
+                            PacketReceiver* receive_transport_receiver) {
     send_transport_.SetReceiver(send_transport_receiver);
     receive_transport_.SetReceiver(receive_transport_receiver);
   }