自定义音频流

前言

AudioStream是所有音频发射对象的基类.AudioStreamPlayer绑定到AudioStream以将PCM数据发送到管理音频驱动程序的AudioServer. 所有音频资源都需要两个基于音频的类:AudioStream和AudioStreamPlayback. 作为数据容器,AudioStream包含资源并将其自身暴露给GDScript.AudioStream引用其自己的内部自定义AudioStreamPlayback, 该AudioStreamPlayback将AudioStream转换为PCM数据. 自定义 C++ 模块.

参考：

  • servers/audio/audio_stream.h
  • scene/audio/audioplayer.cpp

    可以做什么？

  • 绑定外部库(如Wwise, FMOD等).
  • 添加自定义音频队列
  • 添加对更多音频格式的支持

    创建 AudioStream

    AudioStream由三个组件组成: 数据容器, 流名称和AudioStreamPlayback朋友类生成器. 音频数据可以通过多种方式加载, 例如使用用于音调发生器的内部计数器, 内部/外部缓冲区, 或文件引用. load. 因此, 播放状态必须被包含在AudioStreamPlayback中.
    1. /* audiostream_mytone.h */#include "core/reference.h"#include "core/resource.h"#include "servers/audio/audio_stream.h"class AudioStreamMyTone : public AudioStream {        GDCLASS(AudioStreamMyTone, AudioStream)private:        friend class AudioStreamPlaybackMyTone;        uint64_t pos;        int mix_rate;        bool stereo;        int hz;public:        void reset();        void set_position(uint64_t pos);        virtual Ref<AudioStreamPlayback> instance_playback();        virtual String get_stream_name() const;        void gen_tone(int16_t *pcm_buf, int size);        virtual float get_length() const { return 0; } // if supported, otherwise return 0        AudioStreamMyTone();protected:        static void _bind_methods();};
    1. /* audiostream_mytone.cpp */#include "audiostream_mytone.h"AudioStreamMyTone::AudioStreamMyTone()                : mix_rate(44100), stereo(false), hz(639) {}Ref<AudioStreamPlayback> AudioStreamMyTone::instance_playback() {        Ref<AudioStreamPlaybackMyTone> talking_tree;        talking_tree.instance();        talking_tree->base = Ref<AudioStreamMyTone>(this);        return talking_tree;}String AudioStreamMyTone::get_stream_name() const {        return "MyTone";}void AudioStreamMyTone::reset() {        set_position(0);}void AudioStreamMyTone::set_position(uint64_t p) {        pos = p;}void AudioStreamMyTone::gen_tone(int16_t *pcm_buf, int size) {        for (int i = 0; i < size; i++) {                pcm_buf[i] = 32767.0 * sin(2.0 * Math_PI * double(pos + i) / (double(mix_rate) / double(hz)));        }        pos += size;}void AudioStreamMyTone::_bind_methods() {        ClassDB::bind_method(D_METHOD("reset"), &AudioStreamMyTone::reset);        ClassDB::bind_method(D_METHOD("get_stream_name"), &AudioStreamMyTone::get_stream_name);}

    参考：

  • servers/audio/audio_stream.h

    创建 AudioStreamPlayback

    mix 回调来获取PCM数据. 回调必须与采样率匹配并填充缓冲区. 由于AudioStreamPlayback由音频线程控制, 因此禁止进行i/o和动态内存分配.
    1. /*  audiostreamplayer_mytone.h */#include "core/reference.h"#include "core/resource.h"#include "servers/audio/audio_stream.h"class AudioStreamPlaybackMyTone : public AudioStreamPlayback {        GDCLASS(AudioStreamPlaybackMyTone, AudioStreamPlayback)        friend class AudioStreamMyTone;private:        enum {                PCM_BUFFER_SIZE = 4096        };        enum {                MIX_FRAC_BITS = 13,                MIX_FRAC_LEN = (1 << MIX_FRAC_BITS),                MIX_FRAC_MASK = MIX_FRAC_LEN - 1,        };        void *pcm_buffer;        Ref<AudioStreamMyTone> base;        bool active;public:        virtual void start(float p_from_pos = 0.0);        virtual void stop();        virtual bool is_playing() const;        virtual int get_loop_count() const; // times it looped        virtual float get_playback_position() const;        virtual void seek(float p_time);        virtual void mix(AudioFrame *p_buffer, float p_rate_scale, int p_frames);        virtual float get_length() const; // if supported, otherwise return 0        AudioStreamPlaybackMyTone();        ~AudioStreamPlaybackMyTone();};
    1. /* audiostreamplayer_mytone.cpp */#include "audiostreamplayer_mytone.h"#include "core/math/math_funcs.h"#include "core/print_string.h"AudioStreamPlaybackMyTone::AudioStreamPlaybackMyTone()                : active(false) {        AudioServer::get_singleton()->lock();        pcm_buffer = AudioServer::get_singleton()->audio_data_alloc(PCM_BUFFER_SIZE);        zeromem(pcm_buffer, PCM_BUFFER_SIZE);        AudioServer::get_singleton()->unlock();}AudioStreamPlaybackMyTone::~AudioStreamPlaybackMyTone() {        if(pcm_buffer) {                AudioServer::get_singleton()->audio_data_free(pcm_buffer);                pcm_buffer = NULL;        }}void AudioStreamPlaybackMyTone::stop() {        active = false;        base->reset();}void AudioStreamPlaybackMyTone::start(float p_from_pos) {        seek(p_from_pos);        active = true;}void AudioStreamPlaybackMyTone::seek(float p_time) {        float max = get_length();        if (p_time < 0) {                        p_time = 0;        }        base->set_position(uint64_t(p_time * base->mix_rate) << MIX_FRAC_BITS);}void AudioStreamPlaybackMyTone::mix(AudioFrame *p_buffer, float p_rate, int p_frames) {        ERR_FAIL_COND(!active);        if (!active) {                        return;        }        zeromem(pcm_buffer, PCM_BUFFER_SIZE);        int16_t *buf = (int16_t *)pcm_buffer;        base->gen_tone(buf, p_frames);        for(int i = 0; i < p_frames; i++) {                float sample = float(buf[i]) / 32767.0;                p_buffer[i] = AudioFrame(sample, sample);        }}int AudioStreamPlaybackMyTone::get_loop_count() const {        return 0;}float AudioStreamPlaybackMyTone::get_playback_position() const {        return 0.0;}float AudioStreamPlaybackMyTone::get_length() const {        return 0.0;}bool AudioStreamPlaybackMyTone::is_playing() const {        return active;}

    重采样

    Godot的AudioServer目前使用44100Hz采样率. 当需要其他采样率如48000时, 要么提供一个, 要么使用AudioStreamPlaybackResampled.Godot为音频重采样提供立方插值. mix , 而是使用 _mix_internal 来查询AudioFrames, 并使用 get_stream_sampling_rate 来查询当前的混合率.
    1. #include "core/reference.h"#include "core/resource.h"#include "servers/audio/audio_stream.h"class AudioStreamMyToneResampled;class AudioStreamPlaybackResampledMyTone : public AudioStreamPlaybackResampled {        GDCLASS(AudioStreamPlaybackResampledMyTone, AudioStreamPlaybackResampled)        friend class AudioStreamMyToneResampled;private:        enum {                PCM_BUFFER_SIZE = 4096        };        enum {                MIX_FRAC_BITS = 13,                MIX_FRAC_LEN = (1 << MIX_FRAC_BITS),                MIX_FRAC_MASK = MIX_FRAC_LEN - 1,        };        void *pcm_buffer;        Ref<AudioStreamMyToneResampled> base;        bool active;protected:        virtual void _mix_internal(AudioFrame *p_buffer, int p_frames);public:        virtual void start(float p_from_pos = 0.0);        virtual void stop();        virtual bool is_playing() const;        virtual int get_loop_count() const; // times it looped        virtual float get_playback_position() const;        virtual void seek(float p_time);        virtual float get_length() const; // if supported, otherwise return 0        virtual float get_stream_sampling_rate();        AudioStreamPlaybackResampledMyTone();        ~AudioStreamPlaybackResampledMyTone();};
    1. #include "mytone_audiostream_resampled.h"#include "core/math/math_funcs.h"#include "core/print_string.h"AudioStreamPlaybackResampledMyTone::AudioStreamPlaybackResampledMyTone()                : active(false) {        AudioServer::get_singleton()->lock();        pcm_buffer = AudioServer::get_singleton()->audio_data_alloc(PCM_BUFFER_SIZE);        zeromem(pcm_buffer, PCM_BUFFER_SIZE);        AudioServer::get_singleton()->unlock();}AudioStreamPlaybackResampledMyTone::~AudioStreamPlaybackResampledMyTone() {        if (pcm_buffer) {                AudioServer::get_singleton()->audio_data_free(pcm_buffer);                pcm_buffer = NULL;        }}void AudioStreamPlaybackResampledMyTone::stop() {        active = false;        base->reset();}void AudioStreamPlaybackResampledMyTone::start(float p_from_pos) {        seek(p_from_pos);        active = true;}void AudioStreamPlaybackResampledMyTone::seek(float p_time) {        float max = get_length();        if (p_time < 0) {                        p_time = 0;        }        base->set_position(uint64_t(p_time * base->mix_rate) << MIX_FRAC_BITS);}void AudioStreamPlaybackResampledMyTone::_mix_internal(AudioFrame *p_buffer, int p_frames) {        ERR_FAIL_COND(!active);        if (!active) {                return;        }        zeromem(pcm_buffer, PCM_BUFFER_SIZE);        int16_t *buf = (int16_t *)pcm_buffer;        base->gen_tone(buf, p_frames);        for(int i = 0;  i < p_frames; i++) {                float sample = float(buf[i]) / 32767.0;                        p_buffer[i] = AudioFrame(sample, sample);        }}float AudioStreamPlaybackResampledMyTone::get_stream_sampling_rate() {        return float(base->mix_rate);}int AudioStreamPlaybackResampledMyTone::get_loop_count() const {        return 0;}float AudioStreamPlaybackResampledMyTone::get_playback_position() const {        return 0.0;}float AudioStreamPlaybackResampledMyTone::get_length() const {        return 0.0;}bool AudioStreamPlaybackResampledMyTone::is_playing() const {        return active;}

    参考：

  • core/math/audio_frame.h
  • servers/audio/audio_stream.h
  • scene/audio/audioplayer.cpp