AudioEncoder.hpp

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/*
    MIT License
 
    DiscordCoreAPI, A bot library for Discord, written in C++, and featuring explicit multithreading through the usage of custom, asynchronous C++ CoRoutines.
 
    Copyright 2022, 2023 Chris M. (RealTimeChris)
 
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
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    The above copyright notice and this permission notice shall be included in all
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    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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/// AudioEncoder.hpp - Header for the audio encoder class.
/// Aug 22, 2021
/// https://discordcoreapi.com
/// \file AudioEncoder.hpp
#pragma once
 
#include <discordcoreapi/FoundationEntities.hpp>
#include <opus/opus.h>
 
namespace discord_core_api {
 
    namespace discord_core_internal {
 
        /**
         * \addtogroup discord_core_internal
         * @{
         */
 
        /// @brief Structure to hold the encoded data and sample count returned by the encoder.
        struct encoder_return_data {
            jsonifier::string_view_base<uint8_t> data{};///< Encoded data.
            uint64_t sampleCount{};///< Number of audio samples in the input frame.
        };
 
        /// @brief Wrapper class for the opus audio encoder.
        struct opus_encoder_wrapper {
            /// @brief Deleter for OpusEncoder instances.
            struct opus_encoder_deleter {
                /// @brief Operator to destroy an OpusEncoder instance.
                /// @param other the OpusEncoder pointer to be deleted.
                inline void operator()(OpusEncoder* other) {
                    if (other) {
                        opus_encoder_destroy(other);
                        other = nullptr;
                    }
                }
            };
 
            /// @brief Constructor for opus_encoder_wrapper. initializes and configures the opus encoder.
            inline opus_encoder_wrapper() {
                int32_t error{};
                ptr.reset(opus_encoder_create(sampleRate, nChannels, OPUS_APPLICATION_AUDIO, &error));
 
                // set opus signal type to music
                auto result = opus_encoder_ctl(ptr.get(), OPUS_SET_SIGNAL(OPUS_SIGNAL_MUSIC));
                if (result != OPUS_OK) {
                    throw dca_exception{ "Failed to set the opus signal type, reason: " + jsonifier::string{ opus_strerror(result) } };
                }
 
                // set opus bitrate to maximum
                result = opus_encoder_ctl(ptr.get(), OPUS_SET_BITRATE(OPUS_BITRATE_MAX));
                if (result != OPUS_OK) {
                    throw dca_exception{ "Failed to set the opus bitrate, reason: " + jsonifier::string{ opus_strerror(result) } };
                }
            }
 
            /// @brief Encode opus audio data.
            /// @param inputFrame the audio data to encode.
            /// @return encoded data and sample count.
            /// @throws dca_exception if encoding fails.
            inline encoder_return_data encodeData(jsonifier::string_view_base<uint8_t> inputFrame) {
                if (inputFrame.size() == 0) {
                    return {};
                }
 
                if (encodedData.size() == 0) {
                    encodedData.resize(maxBufferSize);
                }
                if (resampleVector.size() < inputFrame.size() / 2) {
                    resampleVector.resize(inputFrame.size() / 2);
                }
                std::memcpy(resampleVector.data(), inputFrame.data(), inputFrame.size());
                uint64_t sampleCount = inputFrame.size() / 2 / 2;
                int32_t count        = opus_encode(ptr.get(), resampleVector.data(), static_cast<int32_t>(inputFrame.size() / 2 / 2), encodedData.data(), maxBufferSize);
                if (count <= 0) {
                    throw dca_exception{ "Failed to encode the bitstream, reason: " + jsonifier::string{ opus_strerror(count) } };
                }
 
                encoder_return_data returnData{};
                returnData.sampleCount = sampleCount;
                returnData.data        = jsonifier::string_view_base<uint8_t>{ encodedData.data(), encodedData.size() };
                return returnData;
            }
 
          protected:
            unique_ptr<OpusEncoder, opus_encoder_deleter> ptr{};///< Unique pointer to OpusEncoder instance.
            jsonifier::vector<opus_int16> resampleVector{};///< For properly copying the values without type-punning.
            jsonifier::string_base<uint8_t> encodedData{};///< Buffer for encoded audio data.
            static constexpr uint64_t maxBufferSize{ 1276 };///< Maximum size of the encoded data buffer.
            static constexpr int64_t sampleRate{ 48000 };///< Sample rate of the audio data.
            static constexpr int64_t nChannels{ 2 };///< Number of audio channels.
        };
 
        /**@}*/
 
    }
 
}