TWCC-PLR -based FecController doesn’t need smoothing

webrtc/common_audio/smoothing_filter.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 93 matching lines @@
       ExtrapolateLastSample(*init_end_time_ms_);
       // Then extrapolate the rest by the following.
     }
     multiplier = powf(alpha_, time_ms - last_state_time_ms_);
   }
 
   state_ = multiplier * state_ + (1.0f - multiplier) * last_sample_;
   last_state_time_ms_ = time_ms;
 }
 
-}  // namespace webrtc
-
 // Appendix: derivation of extrapolation during initialization phase.
 // (LaTeX syntax)
 // Assuming
 //   \begin{align}
 //     y(n) &= \alpha_{n-1} y(n-1) + \left(1 - \alpha_{n-1}\right) x(m) \\*
 //          &= \left(\prod_{i=m}^{n-1} \alpha_i\right) y(m) +
 //             \left(1 - \prod_{i=m}^{n-1} \alpha_i \right) x(m)
 //   \end{align}
 // Taking $\alpha_{n} = \exp(-\gamma^n)$, $\gamma$ denotes init\_factor\_, the
 // multiplier becomes
 //   \begin{align}
 //     \prod_{i=m}^{n-1} \alpha_i
 //     &= \exp\left(-\sum_{i=m}^{n-1} \gamma^i \right) \\*
 //     &= \begin{cases}
 //          \exp\left(-\frac{\gamma^m - \gamma^n}{1 - \gamma} \right)
 //          & \gamma \neq 1 \\*
 //          m-n & \gamma = 1
 //        \end{cases}
 //   \end{align}
 // We know $\gamma = T^{-\frac{1}{T}}$, where $T$ denotes init\_time\_ms\_. Then
 // $1 - \gamma$ approaches zero when $T$ increases. This can cause numerical
 // difficulties. We multiply $T$ (if $T > 0$) to both numerator and denominator
 // in the fraction. See.
 //   \begin{align}
 //     \frac{\gamma^m - \gamma^n}{1 - \gamma}
 //     &= \frac{T^\frac{T-m}{T} - T^\frac{T-n}{T}}{T - T^{1-\frac{1}{T}}}
 //   \end{align}
+
+NullSmoothingFilter::NullSmoothingFilter() = default;
+
+NullSmoothingFilter::~NullSmoothingFilter() = default;
+
+void NullSmoothingFilter::AddSample(float sample) {
+  last_sample_ = rtc::Optional<float>(sample);
+}
+
+rtc::Optional<float> NullSmoothingFilter::GetAverage() {
+  return last_sample_;
+}
+
+bool NullSmoothingFilter::SetTimeConstantMs(int time_constant_ms) {
+  RTC_NOTREACHED();
+  return false;
+}
+
+}  // namespace webrtc