Improved AGC update scheme for the audio backend in Chrome

media/audio/audio_input_stream_impl.cc

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "base/logging.h"
-#include "media/audio/audio_input_stream_impl.h"
-
-namespace media {
-
-static const int kMinIntervalBetweenVolumeUpdatesMs = 1000;
-
-AudioInputStreamImpl::AudioInputStreamImpl()
-    : agc_is_enabled_(false),
-      max_volume_(0.0),
-      normalized_volume_(0.0) {
-}
-
-AudioInputStreamImpl::~AudioInputStreamImpl() {}
-
-void AudioInputStreamImpl::SetAutomaticGainControl(bool enabled) {
-  agc_is_enabled_ = enabled;
-}
-
-bool AudioInputStreamImpl::GetAutomaticGainControl() {
-  return agc_is_enabled_;
-}
-
-void AudioInputStreamImpl::UpdateAgcVolume() {
-  base::AutoLock lock(lock_);
-
-  // We take new volume samples once every second when the AGC is enabled.
-  // To ensure that a new setting has an immediate effect, the new volume
-  // setting is cached here. It will ensure that the next OnData() callback
-  // will contain a new valid volume level. If this approach was not taken,
-  // we could report invalid volume levels to the client for a time period
-  // of up to one second.
-  if (agc_is_enabled_) {
-    GetNormalizedVolume();
-  }
-}
-
-void AudioInputStreamImpl::QueryAgcVolume(double* normalized_volume) {
-  base::AutoLock lock(lock_);
-
-  // Only modify the |volume| output reference if AGC is enabled and if
-  // more than one second has passed since the volume was updated the last time.
-  if (agc_is_enabled_) {
-    base::Time now = base::Time::Now();
-    if ((now - last_volume_update_time_).InMilliseconds() >
-      kMinIntervalBetweenVolumeUpdatesMs) {
-        GetNormalizedVolume();
-        last_volume_update_time_ = now;
-    }
-    *normalized_volume = normalized_volume_;
-  }
-}
-
-void AudioInputStreamImpl::GetNormalizedVolume() {
-  if (max_volume_ == 0.0) {
-    // Cach the maximum volume if this is the first time we ask for it.
-    max_volume_ = GetMaxVolume();
-  }
-
-  if (max_volume_ != 0.0) {
-    // Retrieve the current volume level by asking the audio hardware.
-    // Range is normalized to [0.0,1.0] or [0.0, 1.5] on Linux.
-    normalized_volume_ = GetVolume() / max_volume_;
-  }
-}
-
-}  // namespace media