ChannelMap.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Containers/Array.h"
#include "HAL/Platform.h"
 
namespace Audio
{
    // Maximum number of channels supported by channel maps (Corresponds to 7.1 format)
    static constexpr uint32 ChannelMapMaxNumChannels = 8;
    // Number of channels in a vorbis input (Corresponds to 5.1 with vorbis channel ordering).
    static constexpr uint32 ChannelMapVorbisNumChannels = 6;
 
    enum class EChannelMapOrder : uint8
    {
        // The channel map matrix is in output major order, meaning that adjacent
        // values increment the output channel index.
        //
        // G_In_Om is the gain for input channel (n) and output channel (m).
        // If there are (N) input channels and (M) output channel, then the channel
        // map will be in the form:
        // [ 
        //      G_I0_O0, G_I0_O1, ... G_I0_OM, 
        //      G_I1_O0, G_I1_O1, ... G_I0_OM, 
        //      ...
        //      G_IN_O0, G_IN_O1, ... G_I0_OM, 
        // ]
        OutputMajorOrder,
 
 
        // The channel map matrix is in input major order, meaning that adjacent
        // values increment the input channel index.
        //
        // G_In_Om is the gain for input channel (n) and output channel (m).
        // If there are (N) input channels and (M) output channel, then the channel
        // map will be in the form:
        // [ 
        //      G_I0_O0, G_I1_O0, ... G_IN_O0, 
        //      G_I0_O1, G_I1_O1, ... G_IN_O1, 
        //      ...
        //      G_I0_OM, G_I1_OM, ... G_IN_OM, 
        // ]
        InputMajorOrder
    };
 
    enum class EChannelMapMonoUpmixMethod : uint8
    {
        // The mono channel is split 0.5 left/right
        Linear,
 
        // The mono channel is split 0.707 left/right
        EqualPower,
 
        // The mono channel is split 1.0 left/right
        FullVolume
    };
 
    struct FChannelMapParams
    {
        // Number of channels in the input audio.
        int32 NumInputChannels;
        // Number of channels in the output audio.
        int32 NumOutputChannels;
        // Order of gain coefficients in the output channel map. 
        EChannelMapOrder Order;
        // Method for upmixing mono audio (only used if NumInputChannels == 1)
        EChannelMapMonoUpmixMethod MonoUpmixMethod;
        // If true and (NumInputChannels == 1) and the output format has a center channel,
        // then the mono channel will be routed directly to the center channel.
        bool bIsCenterChannelOnly;
    };
 
    SIGNALPROCESSING_API bool Create2DChannelMap(const FChannelMapParams& InParams, TArray<float>& OutChannelMap);
 
    SIGNALPROCESSING_API bool CreateVorbis2DChannelMap(int32 InNumOutputChannels, EChannelMapOrder InOrder, TArray<float>& OutVorbisChannelMap);
}