Source/WebCore/platform/audio/MultiChannelResampler.cpp

/*
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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "MultiChannelResampler.h"

#include "AudioBus.h"
#include "SincResampler.h"

namespace WebCore {

MultiChannelResampler::MultiChannelResampler(double scaleFactor, unsigned numberOfChannels, unsigned requestFrames, Function<void(AudioBus*, size_t framesToProcess)>&& provideInput)
    : m_numberOfChannels(numberOfChannels)
    , m_provideInput(WTFMove(provideInput))
    , m_multiChannelBus(AudioBus::create(numberOfChannels, requestFrames, false))
{
    // As an optimization, we will use the buffer passed to provideInputForChannel() as channel memory for the first channel so we
    // only need to allocate memory if there is more than one channel.
    if (numberOfChannels > 1) {
        m_channelsMemory.reserveInitialCapacity(numberOfChannels - 1);
        for (unsigned channelIndex = 1; channelIndex < numberOfChannels; ++channelIndex) {
            m_channelsMemory.uncheckedAppend(makeUnique<AudioFloatArray>(requestFrames));
            m_multiChannelBus->setChannelMemory(channelIndex, m_channelsMemory.last()->data(), requestFrames);
        }
    }

    // Create each channel's resampler.
    for (unsigned channelIndex = 0; channelIndex < numberOfChannels; ++channelIndex)
        m_kernels.append(makeUnique<SincResampler>(scaleFactor, requestFrames, std::bind(&MultiChannelResampler::provideInputForChannel, this, std::placeholders::_1, std::placeholders::_2, channelIndex)));
}

MultiChannelResampler::~MultiChannelResampler() = default;

void MultiChannelResampler::process(AudioBus* destination, size_t framesToProcess)
{
    ASSERT(m_numberOfChannels == destination->numberOfChannels());
    if (destination->numberOfChannels() == 1) {
        // Fast path when the bus is mono to avoid the chunking below.
        m_kernels[0]->process(destination->channel(0)->mutableData(), framesToProcess);
        return;
    }

    // We need to ensure that SincResampler only calls provideInputForChannel() once for each channel or it will confuse the logic
    // inside provideInputForChannel(). To ensure this, we chunk the number of requested frames into SincResampler::chunkSize()
    // sized chunks. SincResampler guarantees it will only call provideInputForChannel() once once we resample this way.
    m_outputFramesReady = 0;
    while (m_outputFramesReady < framesToProcess) {
        size_t chunkSize = m_kernels[0]->chunkSize();
        size_t framesThisTime = std::min(framesToProcess - m_outputFramesReady, chunkSize);

        for (unsigned channelIndex = 0; channelIndex < m_numberOfChannels; ++channelIndex) {
            ASSERT(chunkSize == m_kernels[channelIndex]->chunkSize());
            m_kernels[channelIndex]->process(destination->channel(channelIndex)->mutableData() + m_outputFramesReady, framesThisTime);
        }

        m_outputFramesReady += framesThisTime;
    }
}

void MultiChannelResampler::provideInputForChannel(float* buffer, size_t framesToProcess, unsigned channelIndex)
{
    ASSERT(channelIndex < m_multiChannelBus->numberOfChannels());
    ASSERT(framesToProcess == m_multiChannelBus->length());

    if (!channelIndex) {
        // As an optimization, we use the provided buffer as memory for the first channel in the AudioBus. This avoids
        // having to memcpy() for the first channel.
        m_multiChannelBus->setChannelMemory(0, buffer, framesToProcess);
        m_provideInput(m_multiChannelBus.get(), framesToProcess);
        return;
    }

    // Copy the channel data from what we received from m_multiChannelProvider.
    memcpy(buffer, m_multiChannelBus->channel(channelIndex)->data(), sizeof(float) * framesToProcess);
}

} // namespace WebCore

#endif // ENABLE(WEB_AUDIO)