QtFM::AudioOutput Class

The AudioOutput class is the interface of a sound output that an Engine renders into. More…

List of all members, including inherited members

Public Functions

Protected Functions

Detailed Description

Implement open() to start a device or callback at the given rate and format, and call pull() from its audio thread to fill each buffer; close() stops it and must not return until the audio thread has stopped calling pull().

// An output with no device: a thread that pulls blocks as fast as it can, to measure the engine.
class BenchmarkOutput : public AudioOutput {
public:
    bool open(int sampleRate, int channels, SampleFormat format) override {
        Q_UNUSED(format);
        m_rate = sampleRate;
        m_buffer.assign(static_cast<std::size_t>(256 * channels), 0.0f);
        m_running = true;
        m_thread = std::thread([this] {
            while (m_running.load())
                m_frames += pull(m_buffer.data(), 256);
        });
        return true;
    }
    void close() override {
        m_running = false;
        if (m_thread.joinable())
            m_thread.join();
    }
    qint64 frames() const { return m_frames.load(); }
    int rate() const { return m_rate; }

private:
    std::vector<float> m_buffer;
    std::atomic<bool> m_running{false};
    std::atomic<qint64> m_frames{0};
    std::thread m_thread;
    int m_rate = 0;
};

Differences from Qt

Member Function Documentation

QtFM::AudioOutput::AudioOutput()

Constructs an output, not attached to an engine.

[virtual] QtFM::AudioOutput::~AudioOutput()

Destroys the output.

[virtual] void QtFM::AudioOutput::close()

Stops calling pull() and closes the output.

[virtual] bool QtFM::AudioOutput::open(int sampleRate, int channels, SampleFormat format)

Opens the output for sampleRate frames a second of channels channels in format, and starts calling pull(). Returns false if it cannot.

[protected] int QtFM::AudioOutput::pull(float *interleaved, int frames)

Renders frames frames of interleaved stereo into interleaved from the attached engine, and returns the number of frames rendered. Writes silence and returns 0 if no engine is attached.

[protected] int QtFM::AudioOutput::pull(qint16 *interleaved, int frames)

This is an overloaded function.

Renders frames frames of 16-bit interleaved stereo into interleaved.

[protected] void QtFM::AudioOutput::reportUnderrun()

Tells the attached engine that the device ran out of samples, so that it emits Engine::underrun(). Safe to call from the audio thread.