Method createBySampleRateConverting

src/core/AudioBus.cpp:678–761

}

std::unique_ptr<AudioBus> AudioBus::createBySampleRateConverting(const AudioBus * sourceBus, bool mixToMono, float newSampleRate)
{
    // sourceBus's sample-rate must be known.
    ASSERT(sourceBus && sourceBus->sampleRate());

    if (!sourceBus || !sourceBus->sampleRate())
    {
        return nullptr;
    }

    double sourceSampleRate = sourceBus->sampleRate();
    float destinationSampleRate = static_cast<float>(newSampleRate);
    double sampleRateRatio = sourceSampleRate / destinationSampleRate;
    int numberOfSourceChannels = sourceBus->numberOfChannels();

    if (numberOfSourceChannels == Channels::Mono)
    {
        mixToMono = false;  // already mono
    }

    if (sourceSampleRate == destinationSampleRate)
    {
        // No sample-rate conversion is necessary.
        if (mixToMono)
            return AudioBus::createByMixingToMono(sourceBus);

        // Return exact copy.
        return AudioBus::createBufferFromRange(sourceBus, 0, sourceBus->length());
    }

    if (sourceBus->isSilent())
    {
        std::unique_ptr<AudioBus> silentBus(new AudioBus(numberOfSourceChannels, static_cast<int>(sourceBus->length() / sampleRateRatio)));
        silentBus->setSampleRate(newSampleRate);
        return silentBus;
    }

    // First, mix to mono (if necessary) then sample-rate convert.
    const AudioBus * resamplerSourceBus;
    std::unique_ptr<AudioBus> mixedMonoBus;
    if (mixToMono)
    {
        mixedMonoBus = AudioBus::createByMixingToMono(sourceBus);
        resamplerSourceBus = mixedMonoBus.get();
    }
    else
    {
        // Directly resample without down-mixing.
        resamplerSourceBus = sourceBus;
    }

    // Calculate destination length based on the sample-rates.
    int sourceLength = resamplerSourceBus->length();
    int destinationLength = static_cast<int>(sourceLength / sampleRateRatio);

    // Create destination bus with same number of channels.
    int numberOfDestinationChannels = resamplerSourceBus->numberOfChannels();
    std::unique_ptr<AudioBus> destinationBus(new AudioBus(numberOfDestinationChannels, destinationLength));