Update VideoFramePump to pass un-changed frames to encoders.

remoting/codec/video_encoder_vpx.cc

Index: remoting/codec/video_encoder_vpx.cc
diff --git a/remoting/codec/video_encoder_vpx.cc b/remoting/codec/video_encoder_vpx.cc
index c74f0d8ecf5e62c4c9d79d77127fb3408ff84932..708cf3ba24f6a4a0c44d19c8d220290af03a7c51 100644
--- a/remoting/codec/video_encoder_vpx.cc
+++ b/remoting/codec/video_encoder_vpx.cc
@@ -5,7 +5,6 @@
 #include "remoting/codec/video_encoder_vpx.h"
 
 #include "base/bind.h"
-#include "base/command_line.h"
 #include "base/logging.h"
 #include "base/sys_info.h"
 #include "remoting/base/util.h"
@@ -25,9 +24,6 @@ namespace remoting {
 
 namespace {
 
-// Name of command-line flag to enable VP9 to use I444 by default.
-const char kEnableI444SwitchName[] = "enable-i444";
-
 // Number of bytes in an RGBx pixel.
 const int kBytesPerRgbPixel = 4;
 
@@ -103,7 +99,9 @@ void SetVp9CodecParameters(vpx_codec_enc_cfg_t* config,
     config->rc_max_quantizer = 0;
     config->rc_end_usage = VPX_VBR;
   } else {
-    config->rc_min_quantizer = 4;
+    // TODO(wez): Set quantization range to 4-40, once the libvpx encoder is
+    // updated not to output any bits if nothing needs topping-off.
+    config->rc_min_quantizer = 20;
     config->rc_max_quantizer = 30;
     config->rc_end_usage = VPX_CBR;
     // In the absence of a good bandwidth estimator set the target bitrate to a
@@ -268,6 +266,20 @@ scoped_ptr<VideoPacket> VideoEncoderVpx::Encode(
   DCHECK_LE(32, frame.size().width());
   DCHECK_LE(32, frame.size().height());
 
+  // If nothing has changed, then only encode data to top-off from lossy to
+  // lossless quantization.
+  if (frame.updated_region().is_empty()) {
+    // VP8 doesn't support top-off, and VP9's lossless mode doesn't need it.
+    if (!use_vp9_ || lossless_encode_)
+      return nullptr;
+    if (!--topoff_frame_count_) {

[Sergey Ulanov, 2015/05/26 21:57:22]

nit: --topoff_frame_count > 0 (or != 0) would be more readable here

[Wez, 2015/06/09 01:46:20]

Plus, in cleaning it up, I fixed a bug in my implementation... :-/

+      return nullptr;
+    }
+  } else {
+    // Just allow a couple of fully empty frames' worth of top-off.
+    topoff_frame_count_ = 2;

[Sergey Ulanov, 2015/05/26 21:57:22]

topoff_frame_count_ is set even when using VP8, but it's ignored later. Maybe
wrap this while block in if(use_vp9_) {}, to make it clear that topoff applies
only for VP9.

[Wez, 2015/06/09 01:46:20]

Done.

+  }
+
   base::TimeTicks encode_start_time = base::TimeTicks::Now();
 
   // Create or reconfigure the codec to match the size of |frame|.
@@ -348,14 +360,8 @@ VideoEncoderVpx::VideoEncoderVpx(bool use_vp9)
       lossless_encode_(false),
       lossless_color_(false),
       active_map_width_(0),
-      active_map_height_(0) {
-  if (use_vp9_) {
-    // Use I444 colour space, by default, if specified on the command-line.
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            kEnableI444SwitchName)) {
-      SetLosslessColor(true);
-    }
-  }
+      active_map_height_(0),
+      topoff_frame_count_(0) {
 }
 
 void VideoEncoderVpx::Configure(const webrtc::DesktopSize& size) {