Custom AudioStreams

Introducción

AudioStream is the base class of all audio emitting objects. AudioStreamPlayer binds onto an AudioStream to emit PCM data into an AudioServer which manages audio drivers.

Todos los recursos de audio requieren dos clases basadas en audio: AudioStream y AudioStreamPlayback. Como container de datos, AudioStream contiene el recurso y se expone a GDScript. AudioStream hace referencia a su propio AudioStreamPlayback interno personalizado que traduce AudioStream en datos PCM.

This guide assumes the reader knows how to create C++ modules. If not, refer to this guide Custom modules in C++.

What for?

  • Binding external libraries (like Wwise, FMOD, etc).
  • Adding custom audio queues
  • Adding support for more audio formats

Create an AudioStream

Un AudioStream consta de tres componentes: container de datos, nombre del stream y un generador de clases amigables AudioStreamPlayback. Los datos de audio pueden cargarse de varias maneras, por ejemplo, con un contador interno para un generador de tonos, una memoria intermedia interna/externa o una referencia de archivo.

Some AudioStreams need to be stateless such as objects loaded from ResourceLoader. ResourceLoader loads once and references the same object regardless how many times load is called on a specific resource. Therefore, playback state must be self contained in AudioStreamPlayback.

/* 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();
};
/* 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);
}

Create an AudioStreamPlayback

AudioStreamPlayer uses mix callback to obtain PCM data. The callback must match sample rate and fill the buffer.

Since AudioStreamPlayback is controlled by the audio thread, i/o and dynamic memory allocation are forbidden.

/*  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();
};
/* 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;
}

Resampling

Godot’s AudioServer currently uses 44100 Hz sample rate. When other sample rates are needed such as 48000, either provide one or use AudioStreamPlaybackResampled. Godot provides cubic interpolation for audio resampling.

Instead of overloading mix, AudioStreamPlaybackResampled uses _mix_internal to query AudioFrames and get_stream_sampling_rate to query current mix rate.

#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();
};
#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;
}