Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 1640 insertions, 0 deletions

diff --git a/third_party/rust/audio-mixer/.cargo-checksum.json b/third_party/rust/audio-mixer/.cargo-checksum.json
new file mode 100644
index 0000000000..b3cca2f8ef
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diff --git a/third_party/rust/audio-mixer/Cargo.toml b/third_party/rust/audio-mixer/Cargo.toml
new file mode 100644
index 0000000000..085d7c4152
--- /dev/null
+++ b/third_party/rust/audio-mixer/Cargo.toml
@@ -0,0 +1,35 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "audio-mixer"
+version = "0.1.2"
+authors = ["Chun-Min Chang <chun.m.chang@gmail.com>"]
+description = "Mixing audio by the input and output channel layout"
+keywords = ["audio", "mixer", "mixing"]
+categories = ["multimedia::audio"]
+license = "MPL-2.0"
+repository = "https://github.com/ChunMinChang/audio-mixer"
+
+[[bench]]
+name = "benchmark"
+harness = false
+[dependencies.bitflags]
+version = "1.2"
+[dev-dependencies.criterion]
+version = "0.3"
+
+[dev-dependencies.float-cmp]
+version = "0.6"
+[badges.travis-ci]
+repository = "ChunMinChang/audio-mixer"
diff --git a/third_party/rust/audio-mixer/README.md b/third_party/rust/audio-mixer/README.md
new file mode 100644
index 0000000000..79afaccac2
--- /dev/null
+++ b/third_party/rust/audio-mixer/README.md
@@ -0,0 +1,18 @@
+# Audio Mixer
+
+[![Build Status](https://travis-ci.com/ChunMinChang/audio-mixer.svg?branch=master)](https://travis-ci.com/ChunMinChang/audio-mixer)
+
+Mixing audio data from any input channel layout to any output channel layout.
+
+The code here is a refactored version from [cubeb][cubeb]'s [cubeb_mixer(_C/C++_)][cubeb_mixer], which adapts the code from [FFmpeg libswresample's rematrix.c][rematrix] .
+The original implementation is in [cubeb-coreaudio-rs][cubeb-coreaudio-rs]'s [PR23][pr23]
+
+## License
+
+MPL-2
+
+[cubeb]: https://github.com/kinetiknz/cubeb
+[cubeb_mixer]: https://github.com/kinetiknz/cubeb/blob/aa636017aca8f79ebc95fb9f03b9333eaf9fd8fc/src/cubeb_mixer.cpp
+[rematrix]: https://github.com/FFmpeg/FFmpeg/blob/4fa2d5a692f40c398a299acf2c6a20f5b98a3708/libswresample/rematrix.c
+[cubeb-coreaudio-rs]: https://github.com/ChunMinChang/cubeb-coreaudio-rs/
+[pr23]: https://github.com/ChunMinChang/cubeb-coreaudio-rs/pull/23
\ No newline at end of file
diff --git a/third_party/rust/audio-mixer/benches/benchmark.rs b/third_party/rust/audio-mixer/benches/benchmark.rs
new file mode 100644
index 0000000000..11c47e55c7
--- /dev/null
+++ b/third_party/rust/audio-mixer/benches/benchmark.rs
@@ -0,0 +1,95 @@
+use audio_mixer::{Channel, Mixer};
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+
+use std::any::{Any, TypeId};
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let frames = 512;
+    c.bench_function("downmix_f32", |b| {
+        b.iter(|| downmix::<f32>(black_box(frames)))
+    });
+    c.bench_function("downmix_i16", |b| {
+        b.iter(|| downmix::<i16>(black_box(frames)))
+    });
+    c.bench_function("upmix_f32", |b| b.iter(|| upmix::<f32>(black_box(frames))));
+    c.bench_function("upmix_i16", |b| b.iter(|| upmix::<i16>(black_box(frames))));
+}
+
+fn downmix<T>(frames: usize)
+where
+    T: Clone + Default + From<u8> + ?Sized + Any,
+{
+    // Downmix from 5.1 to stereo.
+    let input_channels = [
+        Channel::FrontLeft,
+        Channel::FrontRight,
+        Channel::FrontCenter,
+        Channel::LowFrequency,
+        Channel::BackLeft,
+        Channel::BackRight,
+    ];
+    let output_channels = [Channel::FrontLeft, Channel::FrontRight];
+    mix::<T>(&input_channels, &output_channels, frames);
+}
+
+fn upmix<T>(frames: usize)
+where
+    T: Clone + Default + From<u8> + ?Sized + Any,
+{
+    // upmix from mono to stereo.
+    let input_channels = [Channel::FrontCenter];
+    let output_channels = [Channel::FrontLeft, Channel::FrontRight];
+    mix::<T>(&input_channels, &output_channels, frames);
+}
+
+fn mix<T>(input_channels: &[Channel], output_channels: &[Channel], frames: usize)
+where
+    T: Clone + Default + From<u8> + ?Sized + Any,
+{
+    if TypeId::of::<T>() == TypeId::of::<f32>() {
+        let (input_buffer, mut output_buffer) = create_buffers::<f32>(
+            input_channels.len() * frames,
+            output_channels.len() * frames,
+        );
+        let mut in_buf = input_buffer.chunks(input_channels.len());
+        let mut out_buf = output_buffer.chunks_mut(output_channels.len());
+        let mixer = Mixer::<f32>::new(input_channels, output_channels);
+        for _ in 0..frames {
+            mixer.mix(in_buf.next().unwrap(), out_buf.next().unwrap());
+        }
+    } else if TypeId::of::<T>() == TypeId::of::<i16>() {
+        let (input_buffer, mut output_buffer) = create_buffers::<i16>(
+            input_channels.len() * frames,
+            output_channels.len() * frames,
+        );
+        let mut in_buf = input_buffer.chunks(input_channels.len());
+        let mut out_buf = output_buffer.chunks_mut(output_channels.len());
+        let mixer = Mixer::<i16>::new(input_channels, output_channels);
+        for _ in 0..frames {
+            mixer.mix(in_buf.next().unwrap(), out_buf.next().unwrap());
+        }
+    } else {
+        panic!("Unsupport type");
+    }
+}
+
+fn create_buffers<T: Clone + Default + From<u8>>(
+    input_size: usize,
+    output_size: usize,
+) -> (Vec<T>, Vec<T>) {
+    let mut input_buffer = default_buffer::<T>(input_size);
+    for (i, data) in input_buffer.iter_mut().enumerate() {
+        *data = T::from((i + 1) as u8);
+    }
+    let output_buffer = default_buffer::<T>(output_size);
+    (input_buffer, output_buffer)
+}
+
+fn default_buffer<T: Clone + Default>(size: usize) -> Vec<T> {
+    let mut v = Vec::with_capacity(size);
+    v.resize(size, T::default());
+    v
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);
diff --git a/third_party/rust/audio-mixer/src/channel.rs b/third_party/rust/audio-mixer/src/channel.rs
new file mode 100644
index 0000000000..ef58018ad9
--- /dev/null
+++ b/third_party/rust/audio-mixer/src/channel.rs
@@ -0,0 +1,85 @@
+// The number of channels must be unique and start from 0. They will be treated as indice in the
+// mixing matrix and used to form unique bitflags in the channel map, which is a bitmap.
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum Channel {
+    FrontLeft = 0,
+    FrontRight = 1,
+    FrontCenter = 2,
+    LowFrequency = 3,
+    BackLeft = 4,
+    BackRight = 5,
+    FrontLeftOfCenter = 6,
+    FrontRightOfCenter = 7,
+    BackCenter = 8,
+    SideLeft = 9,
+    SideRight = 10,
+    TopCenter = 11,
+    TopFrontLeft = 12,
+    TopFrontCenter = 13,
+    TopFrontRight = 14,
+    TopBackLeft = 15,
+    TopBackCenter = 16,
+    TopBackRight = 17,
+    Silence = 18,
+}
+
+impl Channel {
+    pub const fn number(self) -> usize {
+        self as usize
+    }
+
+    pub const fn count() -> usize {
+        Channel::Silence as usize + 1
+    }
+
+    pub const fn bitmask(self) -> u32 {
+        1 << self as usize
+    }
+}
+
+bitflags! {
+    pub struct ChannelMap: u32 {
+        const FRONT_LEFT = Channel::FrontLeft.bitmask();
+        const FRONT_RIGHT = Channel::FrontRight.bitmask();
+        const FRONT_CENTER = Channel::FrontCenter.bitmask();
+        const LOW_FREQUENCY = Channel::LowFrequency.bitmask();
+        const BACK_LEFT = Channel::BackLeft.bitmask();
+        const BACK_RIGHT = Channel::BackRight.bitmask();
+        const FRONT_LEFT_OF_CENTER = Channel::FrontLeftOfCenter.bitmask();
+        const FRONT_RIGHT_OF_CENTER = Channel::FrontRightOfCenter.bitmask();
+        const BACK_CENTER = Channel::BackCenter.bitmask();
+        const SIDE_LEFT = Channel::SideLeft.bitmask();
+        const SIDE_RIGHT = Channel::SideRight.bitmask();
+        const TOP_CENTER = Channel::TopCenter.bitmask();
+        const TOP_FRONT_LEFT = Channel::TopFrontLeft.bitmask();
+        const TOP_FRONT_CENTER = Channel::TopFrontCenter.bitmask();
+        const TOP_FRONT_RIGHT = Channel::TopFrontRight.bitmask();
+        const TOP_BACK_LEFT = Channel::TopBackLeft.bitmask();
+        const TOP_BACK_CENTER = Channel::TopBackCenter.bitmask();
+        const TOP_BACK_RIGHT = Channel::TopBackRight.bitmask();
+        const SILENCE = Channel::Silence.bitmask();
+    }
+}
+
+// Avoid printing the following types in debugging context {:?} by declaring them in impl
+// rather than bitflags! {} scope.
+impl ChannelMap {
+    pub const FRONT_2: Self = Self {
+        bits: Self::FRONT_LEFT.bits() | Self::FRONT_RIGHT.bits(),
+    };
+    pub const BACK_2: Self = Self {
+        bits: Self::BACK_LEFT.bits() | Self::BACK_RIGHT.bits(),
+    };
+    pub const FRONT_2_OF_CENTER: Self = Self {
+        bits: Self::FRONT_LEFT_OF_CENTER.bits() | Self::FRONT_RIGHT_OF_CENTER.bits(),
+    };
+    pub const SIDE_2: Self = Self {
+        bits: Self::SIDE_LEFT.bits() | Self::SIDE_RIGHT.bits(),
+    };
+}
+
+impl From<Channel> for ChannelMap {
+    fn from(channel: Channel) -> Self {
+        ChannelMap::from_bits(channel.bitmask()).expect("convert an invalid channel")
+    }
+}
diff --git a/third_party/rust/audio-mixer/src/coefficient.rs b/third_party/rust/audio-mixer/src/coefficient.rs
new file mode 100644
index 0000000000..82ff97dbcf
--- /dev/null
+++ b/third_party/rust/audio-mixer/src/coefficient.rs
@@ -0,0 +1,754 @@
+// The code is based from libcubeb's cubeb_mixer.cpp,
+// which adapts the code from libswresample's rematrix.c
+
+use crate::channel::{Channel, ChannelMap};
+
+use std::fmt::Debug;
+
+const CHANNELS: usize = Channel::count();
+
+#[derive(Debug)]
+enum Error {
+    DuplicateNonSilenceChannel,
+    AsymmetricChannels,
+}
+
+#[derive(Debug)]
+struct ChannelLayout {
+    channels: Vec<Channel>,
+    channel_map: ChannelMap,
+}
+
+impl ChannelLayout {
+    fn new(channels: &[Channel]) -> Result<Self, Error> {
+        let channel_map = Self::get_channel_map(channels)?;
+        Ok(Self {
+            channels: channels.to_vec(),
+            channel_map,
+        })
+    }
+
+    // Except Silence channel, the duplicate channels are not allowed.
+    fn get_channel_map(channels: &[Channel]) -> Result<ChannelMap, Error> {
+        let mut map = ChannelMap::empty();
+        for channel in channels {
+            let bitmask = ChannelMap::from(*channel);
+            if channel != &Channel::Silence && map.contains(bitmask) {
+                return Err(Error::DuplicateNonSilenceChannel);
+            }
+            map.insert(bitmask);
+        }
+        Ok(map)
+    }
+}
+
+#[derive(Debug)]
+pub struct Coefficient<T>
+where
+    T: MixingCoefficient,
+    T::Coef: Copy,
+{
+    input_layout: ChannelLayout,
+    output_layout: ChannelLayout,
+    matrix: Vec<Vec<T::Coef>>,
+    would_overflow_from_coefficient_value: Option<bool>, // Only used when T is i16
+}
+
+impl<T> Coefficient<T>
+where
+    T: MixingCoefficient,
+    T::Coef: Copy,
+{
+    // Given a M-channel input layout and a N-channel output layout, generate a NxM coefficients
+    // matrix m such that out_audio = m * in_audio, where in_audio, out_audio are Mx1, Nx1 matrix
+    // storing input and output audio data in their rows respectively.
+    //
+    // data in channel #1 ▸ │ Silence    │   │ 0, 0, 0, 0 │   │ FrontRight   │ ◂ data in channel #1
+    // data in channel #2 ▸ │ FrontRight │ = │ 1, C, 0, L │ x │ FrontCenter  │ ◂ data in channel #2
+    // data in channel #3 ▸ │ FrontLeft  │   │ 0, C, 1, L │   │ FrontLeft    │ ◂ data in channel #3
+    //                            ▴                 ▴         │ LowFrequency │ ◂ data in channel #4
+    //                            ┊                 ┊                ▴
+    //                            ┊                 ┊                ┊
+    //                        out_audio      mixing matrix m       in_audio
+    //
+    // The FrontLeft, FrontRight, ... etc label the data for front-left, front-right ... etc channel
+    // in both input and output audio data buffer.
+    //
+    // C and L are coefficients mixing input data from front-center channel and low-frequency channel
+    // to front-left and front-right.
+    //
+    // In math, the in_audio and out_audio should be a 2D-matrix with several rows containing only
+    // one column. However, the in_audio and out_audio are passed by 1-D matrix here for convenience.
+    pub fn create(input_channels: &[Channel], output_channels: &[Channel]) -> Self {
+        let input_layout = ChannelLayout::new(input_channels).expect("Invalid input layout");
+        let output_layout = ChannelLayout::new(output_channels).expect("Invalid output layout");
+
+        let mixing_matrix =
+            Self::build_mixing_matrix(input_layout.channel_map, output_layout.channel_map)
+                .unwrap_or_else(|_| Self::get_basic_matrix());
+
+        let coefficient_matrix = Self::pick_coefficients(
+            &input_layout.channels,
+            &output_layout.channels,
+            &mixing_matrix,
+        );
+
+        let normalized_matrix = Self::normalize(T::max_coefficients_sum(), coefficient_matrix);
+
+        let would_overflow = T::would_overflow_from_coefficient_value(&normalized_matrix);
+
+        // Convert the type of the coefficients from f64 to T::Coef.
+        let matrix = normalized_matrix
+            .into_iter()
+            .map(|row| row.into_iter().map(T::coefficient_from_f64).collect())
+            .collect();
+
+        Self {
+            input_layout,
+            output_layout,
+            matrix,
+            would_overflow_from_coefficient_value: would_overflow,
+        }
+    }
+
+    // Return the coefficient for mixing input channel data into output channel.
+    pub fn get(&self, input: usize, output: usize) -> T::Coef {
+        assert!(output < self.matrix.len());
+        assert!(input < self.matrix[output].len());
+        self.matrix[output][input] // Perform copy so T::Coef must implement Copy.
+    }
+
+    pub fn would_overflow_from_coefficient_value(&self) -> Option<bool> {
+        self.would_overflow_from_coefficient_value
+    }
+
+    pub fn input_channels(&self) -> &[Channel] {
+        &self.input_layout.channels
+    }
+
+    pub fn output_channels(&self) -> &[Channel] {
+        &self.output_layout.channels
+    }
+
+    // Given audio input and output channel-maps, generate a CxC mixing coefficients matrix M,
+    // whose indice are ordered by the values defined in enum Channel, such that
+    // output_data(i) = Σ M[i][j] * input_data(j), for all j in [0, C),
+    // where i is in [0, C) and C is the number of channels defined in enum Channel,
+    // output_data and input_data are buffers containing data for channels that are also ordered
+    // by the values defined in enum Channel.
+    //
+    // │ FrontLeft    │   │ 1, 0, ..., 0 │   │ FrontLeft    │ ◂ data in front-left channel
+    // │ FrontRight   │   │ 0, 1, ..., 0 │   │ FrontRight   │ ◂ data in front-right channel
+    // │ FrontCenter  │ = │ ........., 0 │ x │ FrontCenter  │ ◂ data in front-center channel
+    // │ ...........  │   │ ........., 0 |   │ ...........  │ ◂ ...
+    // │ Silence      │   │ 0, 0, ..., 0 |   │ Silence      │ ◂ data in silence channel
+    //        ▴                   ▴                  ▴
+    //    out_audio         coef matrix M          in_audio
+    //
+    // ChannelMap would be used as a hash table to check the existence of channels.
+    #[allow(clippy::cognitive_complexity)]
+    fn build_mixing_matrix(
+        input_map: ChannelMap,
+        output_map: ChannelMap,
+    ) -> Result<[[f64; CHANNELS]; CHANNELS], Error> {
+        // Mixing coefficients constants.
+        use std::f64::consts::FRAC_1_SQRT_2;
+        use std::f64::consts::SQRT_2;
+        const CENTER_MIX_LEVEL: f64 = FRAC_1_SQRT_2;
+        const SURROUND_MIX_LEVEL: f64 = FRAC_1_SQRT_2;
+        const LFE_MIX_LEVEL: f64 = 1.0;
+
+        // The indices of channels in the mixing coefficients matrix.
+        const FRONT_LEFT: usize = Channel::FrontLeft.number();
+        const FRONT_RIGHT: usize = Channel::FrontRight.number();
+        const FRONT_CENTER: usize = Channel::FrontCenter.number();
+        const LOW_FREQUENCY: usize = Channel::LowFrequency.number();
+        const BACK_LEFT: usize = Channel::BackLeft.number();
+        const BACK_RIGHT: usize = Channel::BackRight.number();
+        const FRONT_LEFT_OF_CENTER: usize = Channel::FrontLeftOfCenter.number();
+        const FRONT_RIGHT_OF_CENTER: usize = Channel::FrontRightOfCenter.number();
+        const BACK_CENTER: usize = Channel::BackCenter.number();
+        const SIDE_LEFT: usize = Channel::SideLeft.number();
+        const SIDE_RIGHT: usize = Channel::SideRight.number();
+
+        // Return true if mixable channels are symmetric.
+        fn is_symmetric(map: ChannelMap) -> bool {
+            fn even(map: ChannelMap) -> bool {
+                map.bits().count_ones() % 2 == 0
+            }
+            even(map & ChannelMap::FRONT_2)
+                && even(map & ChannelMap::BACK_2)
+                && even(map & ChannelMap::FRONT_2_OF_CENTER)
+                && even(map & ChannelMap::SIDE_2)
+        }
+
+        if !is_symmetric(input_map) || !is_symmetric(output_map) {
+            return Err(Error::AsymmetricChannels);
+        }
+
+        let mut matrix = Self::get_basic_matrix();
+
+        // Get input channels that are not in the output channels.
+        let unaccounted_input_map = input_map & !output_map;
+
+        // When input has front-center but output has not, and output has front-stereo,
+        // mix input's front-center to output's front-stereo.
+        if unaccounted_input_map.contains(ChannelMap::FRONT_CENTER)
+            && output_map.contains(ChannelMap::FRONT_2)
+        {
+            let coefficient = if input_map.contains(ChannelMap::FRONT_2) {
+                CENTER_MIX_LEVEL
+            } else {
+                FRAC_1_SQRT_2
+            };
+            matrix[FRONT_LEFT][FRONT_CENTER] += coefficient;
+            matrix[FRONT_RIGHT][FRONT_CENTER] += coefficient;
+        }
+
+        // When input has front-stereo but output has not, and output has front-center,
+        // mix input's front-stereo to output's front-center.
+        if unaccounted_input_map.contains(ChannelMap::FRONT_2)
+            && output_map.contains(ChannelMap::FRONT_CENTER)
+        {
+            matrix[FRONT_CENTER][FRONT_LEFT] += FRAC_1_SQRT_2;
+            matrix[FRONT_CENTER][FRONT_RIGHT] += FRAC_1_SQRT_2;
+            if input_map.contains(ChannelMap::FRONT_CENTER) {
+                matrix[FRONT_CENTER][FRONT_CENTER] = CENTER_MIX_LEVEL * SQRT_2;
+            }
+        }
+
+        // When input has back-center but output has not,
+        if unaccounted_input_map.contains(ChannelMap::BACK_CENTER) {
+            // if output has back-stereo, mix input's back-center to output's back-stereo.
+            if output_map.contains(ChannelMap::BACK_2) {
+                matrix[BACK_LEFT][BACK_CENTER] += FRAC_1_SQRT_2;
+                matrix[BACK_RIGHT][BACK_CENTER] += FRAC_1_SQRT_2;
+            // or if output has side-stereo, mix input's back-center to output's side-stereo.
+            } else if output_map.contains(ChannelMap::SIDE_2) {
+                matrix[SIDE_LEFT][BACK_CENTER] += FRAC_1_SQRT_2;
+                matrix[SIDE_RIGHT][BACK_CENTER] += FRAC_1_SQRT_2;
+            // or if output has front-stereo, mix input's back-center to output's front-stereo.
+            } else if output_map.contains(ChannelMap::FRONT_2) {
+                matrix[FRONT_LEFT][BACK_CENTER] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+                matrix[FRONT_RIGHT][BACK_CENTER] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+            // or if output has front-center, mix input's back-center to output's front-center.
+            } else if output_map.contains(ChannelMap::FRONT_CENTER) {
+                matrix[FRONT_CENTER][BACK_CENTER] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+            }
+        }
+
+        // When input has back-stereo but output has not,
+        if unaccounted_input_map.contains(ChannelMap::BACK_2) {
+            // if output has back-center, mix input's back-stereo to output's back-center.
+            if output_map.contains(ChannelMap::BACK_CENTER) {
+                matrix[BACK_CENTER][BACK_LEFT] += FRAC_1_SQRT_2;
+                matrix[BACK_CENTER][BACK_RIGHT] += FRAC_1_SQRT_2;
+            // or if output has side-stereo, mix input's back-stereo to output's side-stereo.
+            } else if output_map.contains(ChannelMap::SIDE_2) {
+                let coefficient = if input_map.contains(ChannelMap::SIDE_2) {
+                    FRAC_1_SQRT_2
+                } else {
+                    1.0
+                };
+                matrix[SIDE_LEFT][BACK_LEFT] += coefficient;
+                matrix[SIDE_RIGHT][BACK_RIGHT] += coefficient;
+            // or if output has front-stereo, mix input's back-stereo to output's side-stereo.
+            } else if output_map.contains(ChannelMap::FRONT_2) {
+                matrix[FRONT_LEFT][BACK_LEFT] += SURROUND_MIX_LEVEL;
+                matrix[FRONT_RIGHT][BACK_RIGHT] += SURROUND_MIX_LEVEL;
+            // or if output has front-center, mix input's back-stereo to output's front-center.
+            } else if output_map.contains(ChannelMap::FRONT_CENTER) {
+                matrix[FRONT_CENTER][BACK_LEFT] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+                matrix[FRONT_CENTER][BACK_RIGHT] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+            }
+        }
+
+        // When input has side-stereo but output has not,
+        if unaccounted_input_map.contains(ChannelMap::SIDE_2) {
+            // if output has back-stereo, mix input's side-stereo to output's back-stereo.
+            if output_map.contains(ChannelMap::BACK_2) {
+                let coefficient = if input_map.contains(ChannelMap::BACK_2) {
+                    FRAC_1_SQRT_2
+                } else {
+                    1.0
+                };
+                matrix[BACK_LEFT][SIDE_LEFT] += coefficient;
+                matrix[BACK_RIGHT][SIDE_RIGHT] += coefficient;
+            // or if output has back-center, mix input's side-stereo to output's back-center.
+            } else if output_map.contains(ChannelMap::BACK_CENTER) {
+                matrix[BACK_CENTER][SIDE_LEFT] += FRAC_1_SQRT_2;
+                matrix[BACK_CENTER][SIDE_RIGHT] += FRAC_1_SQRT_2;
+            // or if output has front-stereo, mix input's side-stereo to output's front-stereo.
+            } else if output_map.contains(ChannelMap::FRONT_2) {
+                matrix[FRONT_LEFT][SIDE_LEFT] += SURROUND_MIX_LEVEL;
+                matrix[FRONT_RIGHT][SIDE_RIGHT] += SURROUND_MIX_LEVEL;
+            // or if output has front-center, mix input's side-stereo to output's front-center.
+            } else if output_map.contains(ChannelMap::FRONT_CENTER) {
+                matrix[FRONT_CENTER][SIDE_LEFT] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+                matrix[FRONT_CENTER][SIDE_RIGHT] += SURROUND_MIX_LEVEL * FRAC_1_SQRT_2;
+            }
+        }
+
+        // When input has front-stereo-of-center but output has not,
+        if unaccounted_input_map.contains(ChannelMap::FRONT_2_OF_CENTER) {
+            // if output has front-stereo, mix input's front-stereo-of-center to output's front-stereo.
+            if output_map.contains(ChannelMap::FRONT_2) {
+                matrix[FRONT_LEFT][FRONT_LEFT_OF_CENTER] += 1.0;
+                matrix[FRONT_RIGHT][FRONT_RIGHT_OF_CENTER] += 1.0;
+            // or if output has front-center, mix input's front-stereo-of-center to output's front-center.
+            } else if output_map.contains(ChannelMap::FRONT_CENTER) {
+                matrix[FRONT_CENTER][FRONT_LEFT_OF_CENTER] += FRAC_1_SQRT_2;
+                matrix[FRONT_CENTER][FRONT_RIGHT_OF_CENTER] += FRAC_1_SQRT_2;
+            }
+        }
+
+        // When input has low-frequency but output has not,
+        if unaccounted_input_map.contains(ChannelMap::LOW_FREQUENCY) {
+            // if output has front-center, mix input's low-frequency to output's front-center.
+            if output_map.contains(ChannelMap::FRONT_CENTER) {
+                matrix[FRONT_CENTER][LOW_FREQUENCY] += LFE_MIX_LEVEL;
+            // or if output has front-stereo, mix input's low-frequency to output's front-stereo.
+            } else if output_map.contains(ChannelMap::FRONT_2) {
+                matrix[FRONT_LEFT][LOW_FREQUENCY] += LFE_MIX_LEVEL * FRAC_1_SQRT_2;
+                matrix[FRONT_RIGHT][LOW_FREQUENCY] += LFE_MIX_LEVEL * FRAC_1_SQRT_2;
+            }
+        }
+
+        Ok(matrix)
+    }
+
+    // Return a CHANNELSxCHANNELS matrix M that is (CHANNELS-1)x(CHANNELS-1) identity matrix
+    // padding with one extra row and one column containing only zero values. The result would be:
+    //
+    //      identity      padding
+    //       matrix       column
+    //          ▾           ▾
+    // ┌┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┐                       i  ┐
+    // │ 1, 0, 0, ..., 0 ┊, 0 │                ◂ 0  ┊ channel i
+    // │ 0, 1, 0, ..., 0 ┊, 0 │                ◂ 1  ┊ for
+    // │ 0, 0, 1, ..., 0 ┊, 0 │                ◂ 2  ┊ audio
+    // │ 0, 0, 0, ..., 0 ┊, 0 │                .    ┊ output
+    // │ ............... ┊    │                .    ┊
+    // │ 0, 0, 0, ..., 1 ┊, 0 │                ◂ 16 ┊
+    // ├┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┼┈┈┈┈┤                ◂ 17 ┊
+    // │ 0, 0, 0, ..., 0 ┊, 0 │ ◂ padding row  ◂ 18 ┊
+    //   ▴  ▴  ▴ ....  ▴    ▴                       ┘
+    // j 0  1  2 ....  17   18
+    // └┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┘
+    // channel j for audio input
+    //
+    // Given an audio input buffer, in_audio, and an output buffer, out_audio,
+    // and their channel data are both ordered by the values defined in enum Channel.
+    // The generated matrix M makes sure that:
+    //
+    // out_audio(i) = in_audio(j), if i == j and both i, j are non-silence channel
+    //              = 0,           if i != j or i, j are silence channel
+    //
+    // │ FrontLeft    │       │ FrontLeft    │ ◂ data in front-left channel
+    // │ FrontRight   │       │ FrontRight   │ ◂ data in front-right channel
+    // │ FrontCenter  │ = M x │ FrontCenter  │ ◂ data in front-center channel
+    // │ ...........  │       │ ...........  │ ◂ ...
+    // │ Silence      │       │ Silence      │ ◂ data in silence channel
+    //        ▴                       ▴
+    //    out_audio               in_audio
+    //
+    // That is,
+    // 1. If the input-channel is silence, it won't be mixed into any channel.
+    // 2. If the output-channel is silence, its output-channel data will be zero (silence).
+    // 3. If input-channel j is different from output-channel i, audio data in input channel j
+    //    won't be mixed into the audio output data in channel i
+    // 4. If input-channel j is same as output-channel i,  audio data in input channel j will be
+    //    copied to audio output data in channel i
+    //
+    fn get_basic_matrix() -> [[f64; CHANNELS]; CHANNELS] {
+        const SILENCE: usize = Channel::Silence.number();
+        let mut matrix = [[0.0; CHANNELS]; CHANNELS];
+        for (i, row) in matrix.iter_mut().enumerate() {
+            if i != SILENCE {
+                row[i] = 1.0;
+            }
+        }
+        matrix
+    }
+
+    // Given is an CHANNELSxCHANNELS mixing matrix whose indice are ordered by the values defined
+    // in enum Channel, and the channel orders of M-channel input and N-channel output, generate a
+    // mixing matrix m such that output_data(i) = Σ m[i][j] * input_data(j), for all j in [0, M),
+    // where i is in [0, N) and {input/output}_data(k) means the data of the number k channel in
+    // the input/output buffer.
+    fn pick_coefficients(
+        input_channels: &[Channel],
+        output_channels: &[Channel],
+        source: &[[f64; CHANNELS]; CHANNELS],
+    ) -> Vec<Vec<f64>> {
+        let mut matrix = Vec::with_capacity(output_channels.len());
+        for output_channel in output_channels {
+            let output_channel_index = output_channel.clone().number();
+            let mut coefficients = Vec::with_capacity(input_channels.len());
+            for input_channel in input_channels {
+                let input_channel_index = input_channel.clone().number();
+                coefficients.push(source[output_channel_index][input_channel_index]);
+            }
+            matrix.push(coefficients);
+        }
+        matrix
+    }
+
+    fn normalize(max_coefficients_sum: f64, mut coefficients: Vec<Vec<f64>>) -> Vec<Vec<f64>> {
+        let mut max_sum: f64 = 0.0;
+        for coefs in &coefficients {
+            max_sum = max_sum.max(coefs.iter().sum());
+        }
+        if max_sum != 0.0 && max_sum > max_coefficients_sum {
+            max_sum /= max_coefficients_sum;
+            for coefs in &mut coefficients {
+                for coef in coefs {
+                    *coef /= max_sum;
+                }
+            }
+        }
+        coefficients
+    }
+}
+
+pub trait MixingCoefficient {
+    type Coef;
+
+    // TODO: These should be private.
+    fn max_coefficients_sum() -> f64; // Used for normalizing.
+    fn coefficient_from_f64(value: f64) -> Self::Coef;
+    // Precheck if overflow occurs when converting value from Self::Coef type to Self type.
+    fn would_overflow_from_coefficient_value(coefficient: &[Vec<f64>]) -> Option<bool>;
+
+    fn to_coefficient_value(value: Self) -> Self::Coef;
+    fn from_coefficient_value(value: Self::Coef, would_overflow: Option<bool>) -> Self;
+}
+
+impl MixingCoefficient for f32 {
+    type Coef = f32;
+
+    fn max_coefficients_sum() -> f64 {
+        f64::from(std::i32::MAX)
+    }
+
+    fn coefficient_from_f64(value: f64) -> Self::Coef {
+        value as Self::Coef
+    }
+
+    fn would_overflow_from_coefficient_value(_coefficient: &[Vec<f64>]) -> Option<bool> {
+        None
+    }
+
+    fn to_coefficient_value(value: Self) -> Self::Coef {
+        value
+    }
+
+    fn from_coefficient_value(value: Self::Coef, would_overflow: Option<bool>) -> Self {
+        assert!(would_overflow.is_none());
+        value
+    }
+}
+
+impl MixingCoefficient for i16 {
+    type Coef = i32;
+
+    fn max_coefficients_sum() -> f64 {
+        1.0
+    }
+
+    fn coefficient_from_f64(value: f64) -> Self::Coef {
+        (value * f64::from(1 << 15)).round() as Self::Coef
+    }
+
+    fn would_overflow_from_coefficient_value(coefficient: &[Vec<f64>]) -> Option<bool> {
+        let mut max_sum: Self::Coef = 0;
+        for row in coefficient {
+            let mut sum: Self::Coef = 0;
+            let mut rem: f64 = 0.0;
+            for coef in row {
+                let target = coef * f64::from(1 << 15) + rem;
+                let value = target.round() as Self::Coef;
+                rem += target - target.round();
+                sum += value.abs();
+            }
+            max_sum = max_sum.max(sum);
+        }
+        Some(max_sum > (1 << 15))
+    }
+
+    fn to_coefficient_value(value: Self) -> Self::Coef {
+        Self::Coef::from(value)
+    }
+
+    fn from_coefficient_value(value: Self::Coef, would_overflow: Option<bool>) -> Self {
+        use std::convert::TryFrom;
+        let would_overflow = would_overflow.expect("would_overflow must have value for i16 type");
+        let mut converted = (value + (1 << 14)) >> 15;
+        // clip the signed integer value into the -32768,32767 range.
+        if would_overflow && ((converted + 0x8000) & !0xFFFF != 0) {
+            converted = (converted >> 31) ^ 0x7FFF;
+        }
+        Self::try_from(converted).expect("Cannot convert coefficient from i32 to i16")
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_create_f32() {
+        test_create::<f32>(MixDirection::Downmix);
+        test_create::<f32>(MixDirection::Upmix);
+    }
+
+    #[test]
+    fn test_create_i16() {
+        test_create::<i16>(MixDirection::Downmix);
+        test_create::<i16>(MixDirection::Upmix);
+    }
+
+    fn test_create<T>(direction: MixDirection)
+    where
+        T: MixingCoefficient,
+        T::Coef: Copy + Debug,
+    {
+        let (input_channels, output_channels) = get_test_channels(direction);
+        let coefficient = Coefficient::<T>::create(&input_channels, &output_channels);
+        println!(
+            "{:?} = {:?} * {:?}",
+            output_channels, coefficient.matrix, input_channels
+        );
+    }
+
+    enum MixDirection {
+        Downmix,
+        Upmix,
+    }
+    fn get_test_channels(direction: MixDirection) -> (Vec<Channel>, Vec<Channel>) {
+        let more = vec![
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontLeft,
+            Channel::LowFrequency,
+            Channel::Silence,
+            Channel::BackCenter,
+        ];
+        let less = vec![
+            Channel::FrontLeft,
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontCenter,
+        ];
+        match direction {
+            MixDirection::Downmix => (more, less),
+            MixDirection::Upmix => (less, more),
+        }
+    }
+
+    #[test]
+    fn test_create_with_duplicate_silience_channels_f32() {
+        test_create_with_duplicate_silience_channels::<f32>()
+    }
+
+    #[test]
+    fn test_create_with_duplicate_silience_channels_i16() {
+        test_create_with_duplicate_silience_channels::<i16>()
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_create_with_duplicate_input_channels_f32() {
+        test_create_with_duplicate_input_channels::<f32>()
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_create_with_duplicate_input_channels_i16() {
+        test_create_with_duplicate_input_channels::<i16>()
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_create_with_duplicate_output_channels_f32() {
+        test_create_with_duplicate_output_channels::<f32>()
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_create_with_duplicate_output_channels_i16() {
+        test_create_with_duplicate_output_channels::<i16>()
+    }
+
+    fn test_create_with_duplicate_silience_channels<T>()
+    where
+        T: MixingCoefficient,
+        T::Coef: Copy,
+    {
+        // Duplicate of Silence channels is allowed on both input side and output side.
+        let input_channels = [
+            Channel::FrontLeft,
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontCenter,
+            Channel::Silence,
+        ];
+        let output_channels = [
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontLeft,
+            Channel::BackCenter,
+            Channel::Silence,
+        ];
+        let _ = Coefficient::<T>::create(&input_channels, &output_channels);
+    }
+
+    fn test_create_with_duplicate_input_channels<T>()
+    where
+        T: MixingCoefficient,
+        T::Coef: Copy,
+    {
+        let input_channels = [
+            Channel::FrontLeft,
+            Channel::Silence,
+            Channel::FrontLeft,
+            Channel::FrontCenter,
+        ];
+        let output_channels = [
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontLeft,
+            Channel::FrontCenter,
+            Channel::BackCenter,
+        ];
+        let _ = Coefficient::<T>::create(&input_channels, &output_channels);
+    }
+
+    fn test_create_with_duplicate_output_channels<T>()
+    where
+        T: MixingCoefficient,
+        T::Coef: Copy,
+    {
+        let input_channels = [
+            Channel::FrontLeft,
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontCenter,
+        ];
+        let output_channels = [
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontLeft,
+            Channel::FrontCenter,
+            Channel::FrontCenter,
+            Channel::BackCenter,
+        ];
+        let _ = Coefficient::<T>::create(&input_channels, &output_channels);
+    }
+
+    #[test]
+    fn test_get_redirect_matrix_f32() {
+        test_get_redirect_matrix::<f32>();
+    }
+
+    #[test]
+    fn test_get_redirect_matrix_i16() {
+        test_get_redirect_matrix::<i16>();
+    }
+
+    fn test_get_redirect_matrix<T>()
+    where
+        T: MixingCoefficient,
+        T::Coef: Copy + Debug + PartialEq,
+    {
+        // Create a matrix that only redirect the channels from input side to output side,
+        // without mixing input audio data to output audio data.
+        fn compute_redirect_matrix<T>(
+            input_channels: &[Channel],
+            output_channels: &[Channel],
+        ) -> Vec<Vec<T::Coef>>
+        where
+            T: MixingCoefficient,
+        {
+            let mut matrix = Vec::with_capacity(output_channels.len());
+            for output_channel in output_channels {
+                let mut row = Vec::with_capacity(input_channels.len());
+                for input_channel in input_channels {
+                    row.push(
+                        if input_channel != output_channel
+                            || input_channel == &Channel::Silence
+                            || output_channel == &Channel::Silence
+                        {
+                            0.0
+                        } else {
+                            1.0
+                        },
+                    );
+                }
+                matrix.push(row);
+            }
+
+            // Convert the type of the coefficients from f64 to T::Coef.
+            matrix
+                .into_iter()
+                .map(|row| row.into_iter().map(T::coefficient_from_f64).collect())
+                .collect()
+        }
+
+        let input_channels = [
+            Channel::FrontLeft,
+            Channel::Silence,
+            Channel::FrontRight,
+            Channel::FrontCenter,
+        ];
+        let output_channels = [
+            Channel::Silence,
+            Channel::FrontLeft,
+            Channel::Silence,
+            Channel::FrontCenter,
+            Channel::BackCenter,
+        ];
+
+        // Get a redirect matrix since the output layout is asymmetric.
+        let coefficient = Coefficient::<T>::create(&input_channels, &output_channels);
+
+        let expected = compute_redirect_matrix::<T>(&input_channels, &output_channels);
+        assert_eq!(coefficient.matrix, expected);
+
+        println!(
+            "{:?} = {:?} * {:?}",
+            output_channels, coefficient.matrix, input_channels
+        );
+    }
+
+    #[test]
+    fn test_normalize() {
+        use float_cmp::approx_eq;
+
+        let m = vec![
+            vec![1.0_f64, 2.0_f64, 3.0_f64],
+            vec![4.0_f64, 6.0_f64, 10.0_f64],
+        ];
+
+        let mut max_row_sum: f64 = std::f64::MIN;
+        for row in &m {
+            max_row_sum = max_row_sum.max(row.iter().sum());
+        }
+
+        // Type of Coefficient doesn't matter here.
+        // If the first argument of normalize >= max_row_sum, do nothing.
+        let n = Coefficient::<f32>::normalize(max_row_sum, m.clone());
+        assert_eq!(n, m);
+
+        // If the first argument of normalize < max_row_sum, do normalizing.
+        let smaller_max = max_row_sum - 0.5_f64;
+        assert!(smaller_max > 0.0_f64);
+        let n = Coefficient::<f32>::normalize(smaller_max, m);
+        let mut max_row_sum: f64 = std::f64::MIN;
+        for row in &n {
+            max_row_sum = max_row_sum.max(row.iter().sum());
+            assert!(row.iter().sum::<f64>() <= smaller_max);
+        }
+        assert!(approx_eq!(f64, smaller_max, max_row_sum));
+    }
+}
diff --git a/third_party/rust/audio-mixer/src/lib.rs b/third_party/rust/audio-mixer/src/lib.rs
new file mode 100644
index 0000000000..10bf54603e
--- /dev/null
+++ b/third_party/rust/audio-mixer/src/lib.rs
@@ -0,0 +1,81 @@
+#[macro_use]
+extern crate bitflags;
+
+mod channel;
+mod coefficient;
+
+// Export Channel outside.
+pub use channel::Channel;
+use coefficient::{Coefficient, MixingCoefficient};
+
+use std::default::Default;
+use std::fmt::Debug;
+use std::ops::{AddAssign, Mul};
+
+// A mixer mixing M-channel input data to N-channel output data.
+// T::Coef is an associated type defined in MixingCoefficient, which indicates the type of the
+// mixing coefficient that would be used for type T. When T is f32, the T::Coef is f32. When T
+// is i16, the T::Coef is i32. When mixing data, a temporary variable with type T::Coef would be
+// created to hold the mixing result. Since the type of input and output audio data is T,
+// the methods provided from MixingCoefficient trait would be used to convert the value between
+// type T and T::Coef.
+#[derive(Debug)]
+pub struct Mixer<T>
+where
+    T: Copy + Debug + MixingCoefficient,
+    T::Coef: AddAssign + Copy + Debug + Default + Mul<T::Coef, Output = T::Coef>,
+{
+    coefficient: Coefficient<T>,
+}
+
+impl<T> Mixer<T>
+where
+    T: Copy + Debug + MixingCoefficient,
+    T::Coef: AddAssign + Copy + Debug + Default + Mul<T::Coef, Output = T::Coef>,
+{
+    pub fn new(input_channels: &[Channel], output_channels: &[Channel]) -> Self {
+        Self {
+            coefficient: Coefficient::create(input_channels, output_channels),
+        }
+    }
+
+    // To mix M-channel audio input data to N-channel output data, the data in output-channel i
+    // is the sum of product of data in input-channel j and the coefficient for mixing from
+    // input-channel j to output-channel i, for all j in M channels. That is,
+    // output_data(i) = Σ coefficient(j, i) * input_data(j), for all j in [0, M),
+    // where i is in [0, N) and coefficient is a function returning mixing coefficient from
+    // input channel j to output channel i.
+    pub fn mix(&self, input_buffer: &[T], output_buffer: &mut [T]) {
+        assert_eq!(
+            input_buffer.len(),
+            self.input_channels().len(),
+            "input slice must have the same size as the input channel's one."
+        );
+        assert_eq!(
+            output_buffer.len(),
+            self.output_channels().len(),
+            "output slice must have the same size as the output channel's one."
+        );
+        for (i, output) in output_buffer.iter_mut().enumerate() {
+            // T must implement Default that returns a zero value from default().
+            let mut value = T::Coef::default(); // Create a zero value.
+            for (j, input) in input_buffer.iter().enumerate() {
+                // T::Coef needs to implement `AddAssign` and `Mul` to make `+=` and `*` work.
+                // T needs to implement `Copy` so `*input` can be copied.
+                value += self.coefficient.get(j, i) * T::to_coefficient_value(*input);
+            }
+            *output = T::from_coefficient_value(
+                value,
+                self.coefficient.would_overflow_from_coefficient_value(),
+            );
+        }
+    }
+
+    pub fn input_channels(&self) -> &[Channel] {
+        &self.coefficient.input_channels()
+    }
+
+    pub fn output_channels(&self) -> &[Channel] {
+        &self.coefficient.output_channels()
+    }
+}
diff --git a/third_party/rust/audio-mixer/src/main.rs b/third_party/rust/audio-mixer/src/main.rs
new file mode 100644
index 0000000000..edd6932d77
--- /dev/null
+++ b/third_party/rust/audio-mixer/src/main.rs
@@ -0,0 +1,50 @@
+extern crate audio_mixer;
+use audio_mixer::{Channel, Mixer};
+
+fn main() {
+    // f32
+    let input_channels = [
+        Channel::FrontLeft,
+        Channel::Silence,
+        Channel::FrontRight,
+        Channel::FrontCenter,
+    ];
+    let output_channels = [Channel::FrontLeft, Channel::FrontRight];
+
+    let mut input_buffer = vec![0.0; input_channels.len()];
+    for (i, data) in input_buffer.iter_mut().enumerate() {
+        *data = (i + 1) as f32;
+    }
+    let mut output_buffer = vec![0.0; output_channels.len()];
+
+    let mixer = Mixer::new(&input_channels, &output_channels);
+
+    mixer.mix(&input_buffer.as_slice(), &mut output_buffer.as_mut_slice());
+    println!("{:?} is mixed to {:?}", input_buffer, output_buffer);
+
+    // i16
+    let input_channels = [
+        Channel::FrontLeft,
+        Channel::Silence,
+        Channel::FrontRight,
+        Channel::FrontCenter,
+        Channel::BackLeft,
+        Channel::SideRight,
+        Channel::LowFrequency,
+        Channel::SideLeft,
+        Channel::BackCenter,
+        Channel::BackRight,
+    ];
+    let output_channels = [Channel::Silence, Channel::FrontRight, Channel::FrontLeft];
+
+    let mut input_buffer = vec![0; input_channels.len()];
+    for (i, data) in input_buffer.iter_mut().enumerate() {
+        *data = (i + 0x7FFE) as i16;
+    }
+    let mut output_buffer = vec![0; output_channels.len()];
+
+    let mixer = Mixer::new(&input_channels, &output_channels);
+
+    mixer.mix(&input_buffer.as_slice(), &mut output_buffer.as_mut_slice());
+    println!("{:?} is mixed to {:?}", input_buffer, output_buffer);
+}