Haydn: Part 1 (#2007)

* Haydn: Part 1

Based on my reverse of audio 11.0.0.

As always, core implementation under LGPLv3 for the same reasons as for Amadeus.

This place the bases of a more flexible audio system while making audout & audin accurate.

This have the following improvements:
- Complete reimplementation of audout and audin.
- Audin currently only have a dummy backend.
- Dramatically reduce CPU usage by up to 50% in common cases (SoundIO and OpenAL).
- Audio Renderer now can output to 5.1 devices when supported.
- Audio Renderer init its backend on demand instead of keeping two up all the time.
- All backends implementation are now in their own project.
- Ryujinx.Audio.Renderer was renamed Ryujinx.Audio and was refactored because of this.

As a note, games having issues with OpenAL haven't improved and will not
because of OpenAL design (stopping when buffers finish playing causing
possible audio "pops" when buffers are very small).

* Update for latest hexkyz's edits on Switchbrew

* audren: Rollback channel configuration changes

* Address gdkchan's comments

* Fix typo in OpenAL backend driver

* Address last comments

* Fix a nit

* Address gdkchan's comments

7 files changed, 833 insertions, 0 deletions

diff --git a/Ryujinx.Audio/Common/AudioBuffer.cs b/Ryujinx.Audio/Common/AudioBuffer.cs
new file mode 100644
index 00000000..853896d5
--- /dev/null
+++ b/Ryujinx.Audio/Common/AudioBuffer.cs
@@ -0,0 +1,53 @@
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+using Ryujinx.Audio.Integration;
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// Represent an audio buffer that will be used by an <see cref="IHardwareDeviceSession"/>.
+    /// </summary>
+    public class AudioBuffer
+    {
+        /// <summary>
+        /// Unique tag of this buffer.
+        /// </summary>
+        /// <remarks>Unique per session</remarks>
+        public ulong BufferTag;
+
+        /// <summary>
+        /// Pointer to the user samples.
+        /// </summary>
+        public ulong DataPointer;
+
+        /// <summary>
+        /// Size of the user samples region.
+        /// </summary>
+        public ulong DataSize;
+
+        /// <summary>
+        ///  The timestamp at which the buffer was played.
+        /// </summary>
+        /// <remarks>Not used but useful for debugging</remarks>
+        public ulong PlayedTimestamp;
+
+        /// <summary>
+        /// The user samples.
+        /// </summary>
+        public byte[] Data;
+    }
+}
diff --git a/Ryujinx.Audio/Common/AudioDeviceSession.cs b/Ryujinx.Audio/Common/AudioDeviceSession.cs
new file mode 100644
index 00000000..fbdb5a75
--- /dev/null
+++ b/Ryujinx.Audio/Common/AudioDeviceSession.cs
@@ -0,0 +1,532 @@
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+using Ryujinx.Audio.Integration;
+using Ryujinx.Common;
+using System;
+using System.Diagnostics;
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// An audio device session.
+    /// </summary>
+    class AudioDeviceSession : IDisposable
+    {
+        /// <summary>
+        /// The volume of the <see cref="AudioDeviceSession"/>.
+        /// </summary>
+        private float _volume;
+
+        /// <summary>
+        /// The state of the <see cref="AudioDeviceSession"/>.
+        /// </summary>
+        private AudioDeviceState _state;
+
+        /// <summary>
+        /// Array of all buffers currently used or released.
+        /// </summary>
+        private AudioBuffer[] _buffers;
+
+        /// <summary>
+        /// The server index inside <see cref="_buffers"/> (appended but not queued to device driver).
+        /// </summary>
+        private uint _serverBufferIndex;
+
+        /// <summary>
+        /// The hardware index inside <see cref="_buffers"/> (queued to device driver).
+        /// </summary>
+        private uint _hardwareBufferIndex;
+
+        /// <summary>
+        /// The released index inside <see cref="_buffers"/> (released by the device driver).
+        /// </summary>
+        private uint _releasedBufferIndex;
+
+        /// <summary>
+        /// The count of buffer appended (server side).
+        /// </summary>
+        private uint _bufferAppendedCount;
+
+        /// <summary>
+        /// The count of buffer registered (driver side).
+        /// </summary>
+        private uint _bufferRegisteredCount;
+
+        /// <summary>
+        /// The count of buffer released (released by the driver side).
+        /// </summary>
+        private uint _bufferReleasedCount;
+
+        /// <summary>
+        /// The released buffer event.
+        /// </summary>
+        private IWritableEvent _bufferEvent;
+
+        /// <summary>
+        /// The session on the device driver.
+        /// </summary>
+        private IHardwareDeviceSession _hardwareDeviceSession;
+
+        /// <summary>
+        /// Max number of buffers that can be registered to the device driver at a time.
+        /// </summary>
+        private uint _bufferRegisteredLimit;
+
+        /// <summary>
+        /// Create a new <see cref="AudioDeviceSession"/>.
+        /// </summary>
+        /// <param name="deviceSession">The device driver session associated</param>
+        /// <param name="bufferEvent">The release buffer event</param>
+        /// <param name="bufferRegisteredLimit">The max number of buffers that can be registered to the device driver at a time</param>
+        public AudioDeviceSession(IHardwareDeviceSession deviceSession, IWritableEvent bufferEvent, uint bufferRegisteredLimit = 4)
+        {
+            _bufferEvent = bufferEvent;
+            _hardwareDeviceSession = deviceSession;
+            _bufferRegisteredLimit = bufferRegisteredLimit;
+
+            _buffers = new AudioBuffer[Constants.AudioDeviceBufferCountMax];
+            _serverBufferIndex = 0;
+            _hardwareBufferIndex = 0;
+            _releasedBufferIndex = 0;
+
+            _bufferAppendedCount = 0;
+            _bufferRegisteredCount = 0;
+            _bufferReleasedCount = 0;
+            _volume = 1.0f;
+            _state = AudioDeviceState.Stopped;
+        }
+
+        /// <summary>
+        /// Get the released buffer event.
+        /// </summary>
+        /// <returns>The released buffer event</returns>
+        public IWritableEvent GetBufferEvent()
+        {
+            return _bufferEvent;
+        }
+
+        /// <summary>
+        /// Get the state of the session.
+        /// </summary>
+        /// <returns>The state of the session</returns>
+        public AudioDeviceState GetState()
+        {
+            Debug.Assert(_state == AudioDeviceState.Started || _state == AudioDeviceState.Stopped);
+
+            return _state;
+        }
+
+        /// <summary>
+        /// Get the total buffer count (server + driver + released).
+        /// </summary>
+        /// <returns>Return the total buffer count</returns>
+        private uint GetTotalBufferCount()
+        {
+            uint bufferCount = _bufferAppendedCount + _bufferRegisteredCount + _bufferReleasedCount;
+
+            Debug.Assert(bufferCount <= Constants.AudioDeviceBufferCountMax);
+
+            return bufferCount;
+        }
+
+        /// <summary>
+        /// Register a new <see cref="AudioBuffer"/> on the server side.
+        /// </summary>
+        /// <param name="buffer">The <see cref="AudioBuffer"/> to register</param>
+        /// <returns>True if the operation succeeded</returns>
+        private bool RegisterBuffer(AudioBuffer buffer)
+        {
+            if (GetTotalBufferCount() == Constants.AudioDeviceBufferCountMax)
+            {
+                return false;
+            }
+
+            _buffers[_serverBufferIndex] = buffer;
+            _serverBufferIndex = (_serverBufferIndex + 1) % Constants.AudioDeviceBufferCountMax;
+            _bufferAppendedCount++;
+
+            return true;
+        }
+
+        /// <summary>
+        /// Flush server buffers to hardware.
+        /// </summary>
+        private void FlushToHardware()
+        {
+            uint bufferToFlushCount = Math.Min(Math.Min(_bufferAppendedCount, 4), _bufferRegisteredLimit - _bufferRegisteredCount);
+
+            AudioBuffer[] buffersToFlush = new AudioBuffer[bufferToFlushCount];
+
+            uint hardwareBufferIndex = _hardwareBufferIndex;
+
+            for (int i = 0; i < buffersToFlush.Length; i++)
+            {
+                buffersToFlush[i] = _buffers[_hardwareBufferIndex];
+
+                _bufferAppendedCount--;
+                _bufferRegisteredCount++;
+
+                hardwareBufferIndex = (hardwareBufferIndex + 1) % Constants.AudioDeviceBufferCountMax;
+            }
+
+            _hardwareBufferIndex = hardwareBufferIndex;
+
+            for (int i = 0; i < buffersToFlush.Length; i++)
+            {
+                _hardwareDeviceSession.QueueBuffer(buffersToFlush[i]);
+            }
+        }
+
+        /// <summary>
+        /// Get the current index of the <see cref="AudioBuffer"/> playing on the driver side.
+        /// </summary>
+        /// <param name="playingIndex">The output index of the <see cref="AudioBuffer"/> playing on the driver side</param>
+        /// <returns>True if any buffer is playing</returns>
+        private bool TryGetPlayingBufferIndex(out uint playingIndex)
+        {
+            if (_bufferRegisteredCount > 0)
+            {
+                playingIndex = (_hardwareBufferIndex - _bufferRegisteredCount) % Constants.AudioDeviceBufferCountMax;
+
+                return true;
+            }
+
+            playingIndex = 0;
+
+            return false;
+        }
+
+        /// <summary>
+        /// Try to pop the <see cref="AudioBuffer"/> playing on the driver side.
+        /// </summary>
+        /// <param name="buffer">The output <see cref="AudioBuffer"/> playing on the driver side</param>
+        /// <returns>True if any buffer is playing</returns>
+        private bool TryPopPlayingBuffer(out AudioBuffer buffer)
+        {
+            if (_bufferRegisteredCount > 0)
+            {
+                uint bufferIndex = (_hardwareBufferIndex - _bufferRegisteredCount) % Constants.AudioDeviceBufferCountMax;
+
+                buffer = _buffers[bufferIndex];
+
+                _buffers[bufferIndex] = null;
+
+                _bufferRegisteredCount--;
+
+                return true;
+            }
+
+            buffer = null;
+
+            return false;
+        }
+
+        /// <summary>
+        /// Try to pop a <see cref="AudioBuffer"/> released by the driver side.
+        /// </summary>
+        /// <param name="buffer">The output <see cref="AudioBuffer"/> released by the driver side</param>
+        /// <returns>True if any buffer has been released</returns>
+        public bool TryPopReleasedBuffer(out AudioBuffer buffer)
+        {
+            if (_bufferReleasedCount > 0)
+            {
+                uint bufferIndex = (_releasedBufferIndex - _bufferReleasedCount) % Constants.AudioDeviceBufferCountMax;
+
+                buffer = _buffers[bufferIndex];
+
+                _buffers[bufferIndex] = null;
+
+                _bufferReleasedCount--;
+
+                return true;
+            }
+
+            buffer = null;
+
+            return false;
+        }
+
+        /// <summary>
+        /// Release a <see cref="AudioBuffer"/>.
+        /// </summary>
+        /// <param name="buffer">The <see cref="AudioBuffer"/> to release</param>
+        private void ReleaseBuffer(AudioBuffer buffer)
+        {
+            buffer.PlayedTimestamp = (ulong)PerformanceCounter.ElapsedNanoseconds;
+
+            _bufferRegisteredCount--;
+            _bufferReleasedCount++;
+
+            _releasedBufferIndex = (_releasedBufferIndex + 1) % Constants.AudioDeviceBufferCountMax;
+        }
+
+        /// <summary>
+        /// Update the released buffers.
+        /// </summary>
+        /// <param name="updateForStop">True if the session is currently stopping</param>
+        private void UpdateReleaseBuffers(bool updateForStop = false)
+        {
+            bool wasAnyBuffersReleased = false;
+
+            while (TryGetPlayingBufferIndex(out uint playingIndex))
+            {
+                if (!updateForStop && !_hardwareDeviceSession.WasBufferFullyConsumed(_buffers[playingIndex]))
+                {
+                    break;
+                }
+
+                if (updateForStop)
+                {
+                    _hardwareDeviceSession.UnregisterBuffer(_buffers[playingIndex]);
+                }
+
+                ReleaseBuffer(_buffers[playingIndex]);
+
+                wasAnyBuffersReleased = true;
+            }
+
+            if (wasAnyBuffersReleased)
+            {
+                _bufferEvent.Signal();
+            }
+        }
+
+        /// <summary>
+        /// Append a new <see cref="AudioBuffer"/>.
+        /// </summary>
+        /// <param name="buffer">The <see cref="AudioBuffer"/> to append</param>
+        /// <returns>True if the buffer was appended</returns>
+        public bool AppendBuffer(AudioBuffer buffer)
+        {
+            if (_hardwareDeviceSession.RegisterBuffer(buffer))
+            {
+                if (RegisterBuffer(buffer))
+                {
+                    FlushToHardware();
+
+                    return true;
+                }
+
+                _hardwareDeviceSession.UnregisterBuffer(buffer);
+            }
+
+            return false;
+        }
+
+        public bool AppendUacBuffer(AudioBuffer buffer, uint handle)
+        {
+            // NOTE: On hardware, there is another RegisterBuffer method taking an handle.
+            // This variant of the call always return false (stubbed?) as a result this logic will never succeed.
+
+            return false;
+        }
+
+        /// <summary>
+        /// Start the audio session.
+        /// </summary>
+        /// <returns>A <see cref="ResultCode"/> reporting an error or a success</returns>
+        public ResultCode Start()
+        {
+            if (_state == AudioDeviceState.Started)
+            {
+                return ResultCode.OperationFailed;
+            }
+
+            _hardwareDeviceSession.Start();
+
+            _state = AudioDeviceState.Started;
+
+            FlushToHardware();
+
+            _hardwareDeviceSession.SetVolume(_volume);
+
+            return ResultCode.Success;
+        }
+
+        /// <summary>
+        /// Stop the audio session.
+        /// </summary>
+        /// <returns>A <see cref="ResultCode"/> reporting an error or a success</returns>
+        public ResultCode Stop()
+        {
+            if (_state == AudioDeviceState.Started)
+            {
+                _hardwareDeviceSession.Stop();
+
+                UpdateReleaseBuffers(true);
+
+                _state = AudioDeviceState.Stopped;
+            }
+
+            return ResultCode.Success;
+        }
+
+        /// <summary>
+        /// Get the volume of the session.
+        /// </summary>
+        /// <returns>The volume of the session</returns>
+        public float GetVolume()
+        {
+            return _hardwareDeviceSession.GetVolume();
+        }
+
+        /// <summary>
+        /// Set the volume of the session.
+        /// </summary>
+        /// <param name="volume">The new volume to set</param>
+        public void SetVolume(float volume)
+        {
+            _volume = volume;
+
+            if (_state == AudioDeviceState.Started)
+            {
+                _hardwareDeviceSession.SetVolume(volume);
+            }
+        }
+
+        /// <summary>
+        /// Get the count of buffer currently in use (server + driver side).
+        /// </summary>
+        /// <returns>The count of buffer currently in use</returns>
+        public uint GetBufferCount()
+        {
+            return _bufferAppendedCount + _bufferRegisteredCount;
+        }
+
+        /// <summary>
+        /// Check if a buffer is present.
+        /// </summary>
+        /// <param name="bufferTag">The unique tag of the buffer</param>
+        /// <returns>Return true if a buffer is present</returns>
+        public bool ContainsBuffer(ulong bufferTag)
+        {
+            uint bufferIndex = (_releasedBufferIndex - _bufferReleasedCount) % Constants.AudioDeviceBufferCountMax;
+
+            for (int i = 0; i < GetTotalBufferCount(); i++)
+            {
+                if (_buffers[bufferIndex].BufferTag == bufferTag)
+                {
+                    return true;
+                }
+
+                bufferIndex = (bufferIndex + 1) % Constants.AudioDeviceBufferCountMax;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Get the count of sample played in this session.
+        /// </summary>
+        /// <returns>The count of sample played in this session</returns>
+        public ulong GetPlayedSampleCount()
+        {
+            if (_state == AudioDeviceState.Stopped)
+            {
+                return 0;
+            }
+            else
+            {
+                return _hardwareDeviceSession.GetPlayedSampleCount();
+            }
+        }
+
+        /// <summary>
+        /// Flush all buffers to the initial state.
+        /// </summary>
+        /// <returns>True if any buffer was flushed</returns>
+        public bool FlushBuffers()
+        {
+            if (_state == AudioDeviceState.Stopped)
+            {
+                return false;
+            }
+
+            uint bufferCount = GetBufferCount();
+
+            while (TryPopReleasedBuffer(out AudioBuffer buffer))
+            {
+                _hardwareDeviceSession.UnregisterBuffer(buffer);
+            }
+
+            while (TryPopPlayingBuffer(out AudioBuffer buffer))
+            {
+                _hardwareDeviceSession.UnregisterBuffer(buffer);
+            }
+
+            if (_bufferRegisteredCount == 0 || (_bufferReleasedCount + _bufferAppendedCount) > Constants.AudioDeviceBufferCountMax)
+            {
+                return false;
+            }
+
+            _bufferReleasedCount += _bufferAppendedCount;
+            _releasedBufferIndex = (_releasedBufferIndex + _bufferAppendedCount) % Constants.AudioDeviceBufferCountMax;
+            _bufferAppendedCount = 0;
+            _hardwareBufferIndex = _serverBufferIndex;
+
+            if (bufferCount > 0)
+            {
+                _bufferEvent.Signal();
+            }
+
+            return true;
+        }
+
+        /// <summary>
+        /// Update the session.
+        /// </summary>
+        public void Update()
+        {
+            if (_state == AudioDeviceState.Started)
+            {
+                UpdateReleaseBuffers();
+                FlushToHardware();
+            }
+        }
+
+        public void Dispose()
+        {
+            Dispose(true);
+        }
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                // Tell the hardware session that we are ending.
+                _hardwareDeviceSession.PrepareToClose();
+
+                // Unregister all buffers
+
+                while (TryPopReleasedBuffer(out AudioBuffer buffer))
+                {
+                    _hardwareDeviceSession.UnregisterBuffer(buffer);
+                }
+
+                while (TryPopPlayingBuffer(out AudioBuffer buffer))
+                {
+                    _hardwareDeviceSession.UnregisterBuffer(buffer);
+                }
+
+                // Finally dispose hardware session.
+                _hardwareDeviceSession.Dispose();
+
+                _bufferEvent.Signal();
+            }
+        }
+    }
+}
diff --git a/Ryujinx.Audio/Common/AudioDeviceState.cs b/Ryujinx.Audio/Common/AudioDeviceState.cs
new file mode 100644
index 00000000..77604525
--- /dev/null
+++ b/Ryujinx.Audio/Common/AudioDeviceState.cs
@@ -0,0 +1,35 @@
+//
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// Audio device state.
+    /// </summary>
+    public enum AudioDeviceState : uint
+    {
+        /// <summary>
+        /// The audio device is started.
+        /// </summary>
+        Started,
+
+        /// <summary>
+        /// The audio device is stopped.
+        /// </summary>
+        Stopped
+    }
+}
diff --git a/Ryujinx.Audio/Common/AudioInputConfiguration.cs b/Ryujinx.Audio/Common/AudioInputConfiguration.cs
new file mode 100644
index 00000000..9aa86569
--- /dev/null
+++ b/Ryujinx.Audio/Common/AudioInputConfiguration.cs
@@ -0,0 +1,46 @@
+//
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+using System.Runtime.InteropServices;
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// Audio user input configuration.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct AudioInputConfiguration
+    {
+        /// <summary>
+        /// The target sample rate of the user.
+        /// </summary>
+        /// <remarks>Only 48000Hz is considered valid, other sample rates will be refused.</remarks>
+        public uint SampleRate;
+
+        /// <summary>
+        /// The target channel count of the user.
+        /// </summary>
+        /// <remarks>Only Stereo and Surround are considered valid, other configurations will be refused.</remarks>
+        /// <remarks>Not used in audin.</remarks>
+        public ushort ChannelCount;
+
+        /// <summary>
+        /// Reserved/unused.
+        /// </summary>
+        private ushort _reserved;
+    }
+}
diff --git a/Ryujinx.Audio/Common/AudioOutputConfiguration.cs b/Ryujinx.Audio/Common/AudioOutputConfiguration.cs
new file mode 100644
index 00000000..a493561f
--- /dev/null
+++ b/Ryujinx.Audio/Common/AudioOutputConfiguration.cs
@@ -0,0 +1,54 @@
+//
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+using Ryujinx.Common.Memory;
+using System.Runtime.InteropServices;
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// Audio system output configuration.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct AudioOutputConfiguration
+    {
+        /// <summary>
+        /// The target sample rate of the system.
+        /// </summary>
+        public uint SampleRate;
+
+        /// <summary>
+        /// The target channel count of the system.
+        /// </summary>
+        public uint ChannelCount;
+
+        /// <summary>
+        /// Reserved/unused
+        /// </summary>
+        public SampleFormat SampleFormat;
+
+        /// <summary>
+        /// Reserved/unused.
+        /// </summary>
+        private Array3<byte> _padding;
+
+        /// <summary>
+        /// The initial audio system state.
+        /// </summary>
+        public AudioDeviceState AudioOutState;
+    }
+}
diff --git a/Ryujinx.Audio/Common/AudioUserBuffer.cs b/Ryujinx.Audio/Common/AudioUserBuffer.cs
new file mode 100644
index 00000000..a0614184
--- /dev/null
+++ b/Ryujinx.Audio/Common/AudioUserBuffer.cs
@@ -0,0 +1,53 @@
+//
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+using System.Runtime.InteropServices;
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// Audio user buffer.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct AudioUserBuffer
+    {
+        /// <summary>
+        /// Pointer to the next buffer (ignored).
+        /// </summary>
+        public ulong NextBuffer;
+
+        /// <summary>
+        /// Pointer to the user samples.
+        /// </summary>
+        public ulong Data;
+
+        /// <summary>
+        /// Capacity of the buffer (unused).
+        /// </summary>
+        public ulong Capacity;
+
+        /// <summary>
+        /// Size of the user samples region.
+        /// </summary>
+        public ulong DataSize;
+
+        /// <summary>
+        /// Offset in the user samples region (unused).
+        /// </summary>
+        public ulong DataOffset;
+    }
+}
diff --git a/Ryujinx.Audio/Common/SampleFormat.cs b/Ryujinx.Audio/Common/SampleFormat.cs
new file mode 100644
index 00000000..bb51bdd3
--- /dev/null
+++ b/Ryujinx.Audio/Common/SampleFormat.cs
@@ -0,0 +1,60 @@
+//
+// Copyright (c) 2019-2021 Ryujinx
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+
+namespace Ryujinx.Audio.Common
+{
+    /// <summary>
+    /// Sample format definition.
+    /// </summary>
+    public enum SampleFormat : byte
+    {
+        /// <summary>
+        /// Invalid sample format.
+        /// </summary>
+        Invalid = 0,
+
+        /// <summary>
+        /// PCM8 sample format. (unsupported)
+        /// </summary>
+        PcmInt8 = 1,
+
+        /// <summary>
+        /// PCM16 sample format.
+        /// </summary>
+        PcmInt16 = 2,
+
+        /// <summary>
+        /// PCM24 sample format. (unsupported)
+        /// </summary>
+        PcmInt24 = 3,
+
+        /// <summary>
+        /// PCM32 sample format.
+        /// </summary>
+        PcmInt32 = 4,
+
+        /// <summary>
+        /// PCM Float sample format.
+        /// </summary>
+        PcmFloat = 5,
+
+        /// <summary>
+        /// ADPCM sample format. (Also known as GC-ADPCM)
+        /// </summary>
+        Adpcm = 6
+    }
+}