osg.AudioStream

osg.AudioStream 是OpenSceneGraph库中用于处理音频流的类。

概述

osg.AudioStream 是一个抽象类，提供了处理音频流的接口，它可以被用来处理不同的音频流格式。该类提供了以下核心功能：

• 打开、关闭音频流
• 读取音频流中的数据
• 获取流的信息，如时长、采样率等

使用方法

为了使用 osg.AudioStream ，需要继承该类，并实现以下方法：

    virtual void play() = 0;
    virtual void pause() = 0;
    virtual void stop() = 0;
    virtual bool isPlaying() const = 0;
    virtual bool isPaused() const = 0;
    virtual bool eos() const = 0;
    virtual void setVolume(float volume) = 0;
    virtual void setBalance(float balance) = 0;
    virtual bool open(const std::string& fileName) = 0;
    virtual bool open(const osgAudio::AudioStreamReader& audioStreamReader) = 0;
    virtual bool close() = 0;
    virtual unsigned int getNumChannels() const = 0;
    virtual unsigned int getNumSamples() const = 0;
    virtual unsigned int getSampleRate() const = 0;
    virtual unsigned int getNumBitsPerSample() const = 0;
    virtual TimeValue getLength() const = 0;
    virtual unsigned int read(unsigned int numSamples, void* buffer) = 0;

上述方法是音频流必须实现的方法。其中，一些核心函数的功能如下：

• play：播放音频流
• pause：暂停音频流
• stop：停止音频流
• isPlaying：检测音频是否正在播放
• isPaused：检测音频是否已经暂停
• eos：检测音频流是否结束
• setVolume：设置音量大小
• open：打开音频流
• close：关闭音频流
• getNumChannels：获取音频通道数
• getNumSamples：获取总采样数
• getSampleRate：获取采样频率
• getNumBitsPerSample：获取每个采样值所占的字节数
• getLength：获取音频流长度
• read：读取指定数量的采样数据到缓冲区

案例

假设我们有一个wav格式的音频文件 "audio.wav"，我们将展示如何使用 osg.AudioStream 来播放文件中的音频流。

#include <osg/Notify>
#include <osgDB/Registry>
#include <osgAudio/AudioStream>
#include <osgAudio/SoundState>
#include <osgViewer/Viewer>

class SimpleAudioStream : public osgAudio::AudioStream
{
public:
    SimpleAudioStream()
        : _audioStreamReader()
    {}

    void play() override {}
    void pause() override {}
    void stop() override {}
    bool isPlaying() const override { return false; }
    bool isPaused() const override { return false; }
    bool eos() const override { return false; }
    void setVolume(float volume) override {}
    void setBalance(float balance) override {}
    bool open(const std::string& fileName) override
    {
        std::string ext = osgDB::getFileExtension(fileName);
        osgDB::Registry::instance()->setReadFileCallback(&_audioStreamReader);
        osgDB::ReaderWriter::ReadResult result = osgDB::readFile(fileName);
        osgDB::Registry::instance()->setReadFileCallback(nullptr);

        return result.valid();
    }

    bool open(const osgAudio::AudioStreamReader& audioStreamReader) override
    {
        _audioStreamReader = audioStreamReader;
        return true;
    }

    bool close() override { return true; }
    unsigned int getNumChannels() const override { return _audioStreamReader.getNumChannels(); }
    unsigned int getNumSamples() const override { return _audioStreamReader.getNumSamples(); }
    unsigned int getSampleRate() const override { return _audioStreamReader.getSampleRate(); }
    unsigned int getNumBitsPerSample() const override { return _audioStreamReader.getNumBitsPerSample(); }
    TimeValue getLength() const override { return _audioStreamReader.getTime(); }
    unsigned int read(unsigned int numSamples, void* buffer) override { return 0; }

private:
    osgAudio::AudioStreamReader _audioStreamReader;
};

int main()
{
    osg::ArgumentParser arguments(&argc, argv);
    osg::ref_ptr<SimpleAudioStream> audioStream = new SimpleAudioStream();
    audioStream->open("audio.wav");

    osg::ref_ptr<osgAudio::SoundState> soundState = new osgAudio::SoundState();
    soundState->setAudioStream(audioStream.get());
    soundState->setLooping(true);
    soundState->play();

    osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer();
    viewer->setSceneData(soundState.get());
    return viewer->run();
}

在上述代码中，我们通过 osgDB 来读取音频文件，实现了 open 方法。我们还创建了一个 osgAudio::SoundState 对象，将 SimpleAudioStream 对象设置为其音频流。最后，我们通过 osgViewer::Viewer 类来展示这个音频文件。

参考资料

• osg.AudioStream