Use different restrictions of acked bitrate lag depending on operating point.

webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc

Index: webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc b/webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc
index 530453d74cc1612c105de25bb7cc0280d261c53a..6449f240bff64afc2586cb7cea5a1ec13e83ecfb 100644
--- a/webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc
+++ b/webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc
@@ -229,10 +229,13 @@ uint32_t AimdRateControl::ChangeBitrate(uint32_t current_bitrate_bps,
     default:
       assert(false);
   }
-  if ((incoming_bitrate_bps > 100000 || current_bitrate_bps > 150000) &&
-      current_bitrate_bps > 1.5 * incoming_bitrate_bps) {
-    // Allow changing the bit rate if we are operating at very low rates
-    // Don't change the bit rate if the send side is too far off
+  // We allow a bit more lag at very low rates to not too easily get stuck if
+  // the encoder produces uneven outputs.
+  const uint32_t max_allowed_lag_kbps =

[terelius, 2016/12/02 15:30:13]

Could we rename this max_bitrate_bps? Lag makes me think of the time lag between
the network change and when we update the what the encoder target. Also, it is
measured in bps.

[stefan-webrtc, 2016/12/02 16:16:13]

Done.

+      static_cast<uint32_t>(1.5f * incoming_bitrate_bps) + 10000;
+  if (current_bitrate_bps > current_bitrate_bps_ &&
+      current_bitrate_bps > max_allowed_lag_kbps) {
+    // Don't change the bit rate if the send side is too far off.

[terelius, 2016/12/02 15:30:13]

Place this comment above if-statement and other comment? 

[stefan-webrtc, 2016/12/02 16:16:14]

Done.

     current_bitrate_bps = current_bitrate_bps_;

[terelius, 2016/12/02 15:30:13]

If max_allowed_lag_kbps is the cap and we are above the cap, shouldn't we update
the bitrate to max_allowed_lag_kbps?

Maybe we can replace the entire if-statement with
current_bitrate_bps = std::max(current_bitrate_bps, max_bitrate_bps)?

[stefan-webrtc, 2016/12/02 16:16:14]

Done as discussed.

     time_last_bitrate_change_ = now_ms;
   }