[chromecast] Slew stream volume changes in StreamMixerAlsa.

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

Index: chromecast/media/cma/backend/alsa/slew_volume.cc
diff --git a/chromecast/media/cma/backend/alsa/slew_volume.cc b/chromecast/media/cma/backend/alsa/slew_volume.cc
new file mode 100644
index 0000000000000000000000000000000000000000..95a5d5dced39a8dc5c0b97ad2630d06fd0a4b7b2
--- /dev/null
+++ b/chromecast/media/cma/backend/alsa/slew_volume.cc
@@ -0,0 +1,151 @@
+// 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;
+}
+
+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)

[wzhong, 2016/09/19 04:48:13]

Please add period.

+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(bool repeat_transition,
+                             const float* src,
+                             int frames,
+                             float* dest) {
+  DCHECK(src);
+  DCHECK(dest);
+  // Ensure |src| and |dest| are 16-byte aligned.
+  DCHECK_EQ(0u, reinterpret_cast<uintptr_t>(src) &
+                    (::media::vector_math::kRequiredAlignment - 1));
+  DCHECK_EQ(0u, reinterpret_cast<uintptr_t>(dest) &
+                    (::media::vector_math::kRequiredAlignment - 1));
+
+  if (!frames) {
+    return;
+  }
+
+  if (repeat_transition) {
+    current_volume_ = last_starting_volume_;
+  } else {
+    last_starting_volume_ = current_volume_;
+  }
+
+  if (current_volume_ == volume_scale_) {
+    if (current_volume_ == 0.0) {
+      return;
+    }
+    ::media::vector_math::FMAC(src, current_volume_, frames, dest);
+    return;
+  } else if (current_volume_ < volume_scale_) {

[wzhong, 2016/09/19 04:48:13]

Nit: else is not needed.

+    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
+// on pineapple.
+// Assumes 2 channel audio.
+bool SlewVolume::ProcessInterleaved(int32_t* data, int frames) {
+  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] *= current_volume_;
+    }
+    return true;
+  } else if (current_volume_ < volume_scale_) {

[wzhong, 2016/09/19 04:48:13]

Ditto.

+    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