Duck and mute

base/cvd/cuttlefish/host/frontend/webrtc/BUILD.bazel

@@ -88,6 +88,18 @@ cf_cc_library(
     ],
 )
 
+cf_cc_library(
+    name = "libcuttlefish_webrtc_audio_channel_matrix",
+    srcs = ["audio_channel_matrix.cpp"],
+    hdrs = ["audio_channel_matrix.h"],
+    clang_format_enabled = False,
+    depend_on_what_you_use_enabled = False,
+    include_cleaner_enabled = False,
+    deps = [
+        ":libcuttlefish_webrtc_audio_settings",
+    ],
+)
+
 cf_cc_library(
     name = "libcuttlefish_webrtc_audio_mixer",
     srcs = ["audio_mixer.cpp"],
@@ -96,6 +108,7 @@ cf_cc_library(
     depend_on_what_you_use_enabled = False,
     include_cleaner_enabled = False,
     deps = [
+        ":libcuttlefish_webrtc_audio_channel_matrix",
         ":libcuttlefish_webrtc_audio_settings",
         "//cuttlefish/host/frontend/webrtc/libdevice:audio_sink",
         "//libbase",

base/cvd/cuttlefish/host/frontend/webrtc/audio_channel_matrix.cpp

@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2026 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cuttlefish/host/frontend/webrtc/audio_channel_matrix.h"
+
+#include <algorithm>
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+#include "cuttlefish/host/frontend/webrtc/audio_settings.h"
+
+namespace cuttlefish {
+namespace {
+
+constexpr float kMinus3dB = 0.7071f;  // 1 / sqrt(2) for Center & Surround
+constexpr float kMinus6dB = 0.5000f;  // 1 / 2 for LFE (Subwoofer) and Stereo-to-Mono
+constexpr float kDuckingGain = 0.2000f; // -14 dB (AAOS standard ducking)
+
+}  // namespace
+
+std::vector<std::vector<float>> BuildChannelMixingMatrix(
+    uint8_t dst_channels, uint8_t src_channels, float volume, float fade,
+    float balance, bool is_ducked) {
+  constexpr uint8_t kMono = GetChannelsCount(AudioChannelsLayout::Mono);        // 1
+  constexpr uint8_t kStereo = GetChannelsCount(AudioChannelsLayout::Stereo);    // 2
+  constexpr uint8_t kSurround51 =
+      GetChannelsCount(AudioChannelsLayout::Surround51);                        // 6
+
+  // 1. Fold ducking into effective volume
+  const float duck_factor = is_ducked ? kDuckingGain : 1.0f;
+  const float effective_volume = volume * duck_factor;
+
+  // Compute acoustic cabin attenuation for the 4 quadrants
+  const float front_gain = (fade >= 0.0f) ? 1.0f : (1.0f + fade);
+  const float rear_gain = (fade <= 0.0f) ? 1.0f : (1.0f - fade);
+  const float left_gain = (balance <= 0.0f) ? 1.0f : (1.0f - balance);
+  const float right_gain = (balance >= 0.0f) ? 1.0f : (1.0f + balance);
+
+  const float fl_gain = effective_volume * (front_gain * left_gain);
+  const float fr_gain = effective_volume * (front_gain * right_gain);
+  const float fc_gain = effective_volume * front_gain;
+  const float rl_gain = effective_volume * (rear_gain * left_gain);
+  const float rr_gain = effective_volume * (rear_gain * right_gain);
+
+  // Case 1: Stereo Destination Output (Laptop Speakers / WebRTC sink)
+  if (dst_channels == kStereo) {
+    if (src_channels == kSurround51) {
+      // 5.1 Surround -> Stereo (ITU-R BS.775 with left/right balance & front/rear fade)
+      return {
+          {fl_gain, 0.0f, kMinus3dB * fc_gain * left_gain,
+           kMinus6dB * effective_volume * left_gain, kMinus3dB * rl_gain, 0.0f},
+          {0.0f, fr_gain, kMinus3dB * fc_gain * right_gain,
+           kMinus6dB * effective_volume * right_gain, 0.0f, kMinus3dB * rr_gain},
+      };
+    }
+    if (src_channels == kStereo) {
+      // Stereo -> Stereo (Direct with left/right balance & front/rear fade)
+      return {
+          {fl_gain, 0.0f},
+          {0.0f, fr_gain},
+      };
+    }
+    if (src_channels == kMono) {
+      // Mono -> Stereo (Center mono panned by balance)
+      return {
+          {fl_gain},
+          {fr_gain},
+      };
+    }
+  }
+
+  // Case 2: Mono Destination Output
+  if (dst_channels == kMono) {
+    if (src_channels == kSurround51) {
+      return {
+          {kMinus3dB * fl_gain, kMinus3dB * fr_gain, fc_gain,
+           kMinus6dB * effective_volume, kMinus3dB * rl_gain, kMinus3dB * rr_gain},
+      };
+    }
+    if (src_channels == kStereo) {
+      return {
+          {kMinus6dB * fl_gain, kMinus6dB * fr_gain},
+      };
+    }
+    if (src_channels == kMono) {
+      return {
+          {fl_gain},
+      };
+    }
+  }
+
+  // Fallback: generic diagonal matrix
+  std::vector<std::vector<float>> matrix(
+      dst_channels, std::vector<float>(src_channels, 0.0f));
+  const std::array<float, 6> spatial_gains = {fl_gain, fr_gain, fc_gain,
+                                              effective_volume,  rl_gain, rr_gain};
+  for (size_t i = 0; i < std::min(dst_channels, src_channels); ++i) {
+    matrix[i][i] = (i < spatial_gains.size()) ? spatial_gains[i] : effective_volume;
+  }
+  return matrix;
+}
+
+}  // namespace cuttlefish

base/cvd/cuttlefish/host/frontend/webrtc/audio_channel_matrix.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2026 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cstdint>
+#include <vector>
+
+namespace cuttlefish {
+
+/**
+ * Builds the channel mixing matrix of dimension [dst_channels][src_channels].
+ *
+ * Implements standard ITU-R BS.775 downmixing (e.g. 5.1 -> Stereo, 5.1 -> Mono)
+ * combined with per-stream spatial cabin attenuation (fade and balance).
+ *
+ * @param dst_channels Destination speaker channels (e.g. 2 for Stereo host sink)
+ * @param src_channels Source stream channels (e.g. 6 for 5.1 Surround, 2 for Stereo)
+ * @param volume Master stream volume [0.0 - 1.0]
+ * @param fade Front/Rear cabin fader [-1.0 (Rear) to 1.0 (Front)]
+ * @param balance Left/Right cabin balance [-1.0 (Left) to 1.0 (Right)]
+ * @param is_ducked Whether the stream is ducked (-14 dB attenuation)
+ */
+std::vector<std::vector<float>> BuildChannelMixingMatrix(
+    uint8_t dst_channels, uint8_t src_channels, float volume, float fade,
+    float balance, bool is_ducked = false);
+
+}  // namespace cuttlefish