[chromecast] Slew stream volume changes in StreamMixerAlsa.

chromecast/media/cma/backend/alsa/slew_volume.cc

+// Copyright 2016 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 "chromecast/media/cma/backend/alsa/slew_volume.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "media/base/vector_math.h"
+
+namespace {
+
+// The time to slew from 0.0 to 1.0.
+const int kMaxSlewTimeMs = 100;
+const int kDefaultSampleRate = 44100;
+// ::media::base::FMAC requires |src| to be 16-byte aligned
+const int kRequiredAlignment = 16;

[kmackay, 2016/09/15 01:51:36]

not used?

[jyw, 2016/09/15 22:16:22]

Done.

+}
+
+namespace chromecast {
+namespace media {
+
+SlewVolume::SlewVolume() : SlewVolume(kMaxSlewTimeMs, kMaxSlewTimeMs) {}
+
+SlewVolume::SlewVolume(int max_slew_time_up_ms, int max_slew_time_down_ms)
+    : max_slew_time_up_ms_(max_slew_time_up_ms),
+      max_slew_time_down_ms_(max_slew_time_down_ms),
+      max_slew_up_(1000.0 / (max_slew_time_up_ms * kDefaultSampleRate)),
+      max_slew_down_(1000.0 / (max_slew_time_down_ms * kDefaultSampleRate)) {}
+
+// Slew rate should be 1 / (slew_time * sample_rate)
+void SlewVolume::SetSampleRate(int sample_rate) {
+  max_slew_up_ = (1000.0 / (max_slew_time_up_ms_ * sample_rate));
+  max_slew_down_ = (1000.0 / (max_slew_time_down_ms_ * sample_rate));
+}
+
+void SlewVolume::SetVolume(double volume_scale) {
+  volume_scale_ = volume_scale;
+}
+
+void SlewVolume::ProcessFMAC(const float* src, int frames, float* dest) {
+  DCHECK(src);
+  DCHECK(dest);
+
+  if (!frames) {
+    return;
+  }
+
+  if (current_volume_ == volume_scale_) {
+    if (current_volume_ == 0.0) {
+      return;
+    }

[kmackay, 2016/09/15 01:51:36]

Include alignment requirements in the header comments for this function.

[jyw, 2016/09/15 22:16:23]

Done.

+    ::media::vector_math::FMAC(src, current_volume_, frames, dest);
+    return;
+  } else if (current_volume_ < volume_scale_) {
+    do {
+      (*dest) += (*src) * current_volume_;
+      ++src;
+      ++dest;
+      --frames;
+      current_volume_ += max_slew_up_;
+    } while (current_volume_ < volume_scale_ && frames);
+    current_volume_ = std::min(current_volume_, volume_scale_);
+  } else {  // current_volume_ > volume_scale_
+    do {
+      (*dest) += (*src) * current_volume_;
+      ++src;
+      ++dest;
+      --frames;
+      current_volume_ -= max_slew_down_;
+    } while (current_volume_ > volume_scale_ && frames);
+    current_volume_ = std::max(current_volume_, volume_scale_);
+  }
+
+  if (frames) {
+    for (int f = 0; f < frames; ++f) {
+      dest[f] += src[f] * current_volume_;
+    }
+  }
+}
+
+// Scaling samples naively like this takes 0.2% of the CPU's time @ 44100hz
+// (profiled with waves_standalone).
+// Assumes 2 channel audio.
+bool SlewVolume::ProcessInterleaved(int32_t* data, int frames) {

[kmackay, 2016/09/15 01:51:36]

this one also only ever returns true.

[jyw, 2016/09/15 22:16:22]

There's an internal callsite for ProcessInterleaved() where it makes sense to
return a bool.

+  DCHECK(data);
+
+  if (!frames) {
+    return true;
+  }
+
+  if (current_volume_ == volume_scale_) {
+    if (current_volume_ == 1.0) {
+      return true;
+    }
+    for (int i = 0; i < 2 * frames; ++i) {
+      data[i] *= volume_scale_;

[kmackay, 2016/09/15 01:51:36]

*= current_volume_, for consistency

[jyw, 2016/09/15 22:16:22]

Done.

+    }
+    return true;
+  } else if (current_volume_ < volume_scale_) {
+    do {
+      (*data) *= current_volume_;
+      ++data;
+      (*data) *= current_volume_;
+      ++data;
+      --frames;
+      current_volume_ += max_slew_up_;
+    } while (current_volume_ < volume_scale_ && frames);
+    current_volume_ = std::min(current_volume_, volume_scale_);
+  } else {
+    do {
+      (*data) *= current_volume_;
+      ++data;
+      (*data) *= current_volume_;
+      ++data;
+      --frames;
+      current_volume_ -= max_slew_down_;
+    } while (current_volume_ > volume_scale_ && frames);
+    current_volume_ = std::max(current_volume_, volume_scale_);
+  }
+
+  if (current_volume_ == 1.0) {
+    return true;
+  }
+
+  if (current_volume_ == 0.0) {
+    std::fill_n(data, frames * 2, 0);
+    return true;
+  }
+
+  for (int i = 0; i < 2 * frames; ++i) {
+    data[i] *= current_volume_;
+  }
+  return true;
+}
+
+}  // namespace media
+}  // namespace chromecast