qffmpegaudioframeconverter.cpp

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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qffmpegaudioframeconverter_p.h"
 
#include <QtMultimedia/private/qaudiobuffer_support_p.h>
#include <QtFFmpegMediaPluginImpl/private/qffmpegframe_p.h>
#include <QtFFmpegMediaPluginImpl/private/qffmpegresampler_p.h>
#include <QtFFmpegMediaPluginImpl/private/qffmpegmediaformatinfo_p.h>
 
#if defined(Q_CC_MSVC) && defined(QT_MM_OPTIMIZE_DEBUG)
#  pragma optimize("s", on)
#endif
 
// TODO: namespace 3p library to prevent odr violations
#include <signalsmith-stretch.h>
 
QT_BEGIN_NAMESPACE
 
namespace QFFmpeg {
 
namespace {
 
qreal sampleRateFactor()
{
    // Test purposes:
    //
    // The env var describes a factor for the sample rate of
    // audio data that we feed to the audio sink.
    //
    // In some cases  audio sink might consume data slightly slower or faster than expected;
    // even though the synchronization in the audio renderer is supposed to handle it,
    // it makes sense to experiment with QT_MEDIA_PLAYER_AUDIO_SAMPLE_RATE_FACTOR != 1.
    //
    // Set QT_MEDIA_PLAYER_AUDIO_SAMPLE_RATE_FACTOR > 1 (e.g. 1.01 - 1.1) to test high buffer
    // loading
    //     or try compensating too fast data consumption by the audio sink.
    // Set QT_MEDIA_PLAYER_AUDIO_SAMPLE_RATE_FACTOR < 1 to test low buffer loading
    //     or try compensating too slow data consumption by the audio sink.
 
    static const qreal result = []() {
        const auto sampleRateFactorStr =
                qEnvironmentVariable("QT_MEDIA_PLAYER_AUDIO_SAMPLE_RATE_FACTOR");
        bool ok = false;
        const auto result = sampleRateFactorStr.toDouble(&ok);
        return ok ? result : 1.;
    }();
 
    return result;
}
 
struct TrivialAudioFrameConverter : AbstractAudioFrameConverter
{
    explicit TrivialAudioFrameConverter(const Frame &frame, QAudioFormat outputFormat,
                                        float playbackRate)
    {
        int sampleRate = qRound(outputFormat.sampleRate() / playbackRate * sampleRateFactor());
        outputFormat.setSampleRate(sampleRate);
        m_converter = createResampler(frame, outputFormat);
    }
 
    QAudioBuffer convert(AVFrame *frame) override { return m_converter->resample(frame); }
 
private:
    std::unique_ptr<QFFmpegResampler> m_converter;
};
 
struct PitchShiftingAudioFrameConverter : AbstractAudioFrameConverter
{
    explicit PitchShiftingAudioFrameConverter(const Frame &frame, QAudioFormat outputFormat,
                                              float playbackRate)
        : m_playbackRate{ playbackRate }
    {
        const QAudioFormat mediaFormat = QFFmpegMediaFormatInfo::audioFormatFromCodecParameters(
                *frame.codecContext()->stream()->codecpar);
 
        const QAudioFormat floatFormat = [&] {
            QAudioFormat ret = mediaFormat;
            ret.setSampleFormat(QAudioFormat::SampleFormat::Float);
            return ret;
        }();
 
        m_toPCMDecoder = createResampler(frame, floatFormat); // this is *not* a resampler
        m_stretcher.reset();
        m_pendingFractionalFrames = 0.f;
        m_stretcher.presetDefault(mediaFormat.channelCount(), outputFormat.sampleRate());
 
        const QAudioFormat pitchCompensatedFormat = [&] {
            QAudioFormat ret = floatFormat;
            ret.setSampleRate(outputFormat.sampleRate());
            return ret;
        }();
        m_toOutputFormatConverter = std::make_unique<QFFmpegResampler>(
                pitchCompensatedFormat, outputFormat, frame.startTime().get());
    }
 
    QAudioBuffer convert(AVFrame *frame) override
    {
        using namespace QtPrivate;
 
        // convert to pcm buffer
        QAudioBuffer wordConverted = m_toPCMDecoder->resample(frame);
 
        // compute stretch amount
        int mediaFrameCount = wordConverted.frameCount();
        float expectedNumberOfFrames = mediaFrameCount / m_playbackRate + m_pendingFractionalFrames;
        int numberOfFullExpectedFrames = qFloor(expectedNumberOfFrames);
        m_pendingFractionalFrames = expectedNumberOfFrames - numberOfFullExpectedFrames;
 
        auto timeStretcherOutput = QAudioBuffer{
            numberOfFullExpectedFrames,
            wordConverted.format(),
        };
 
        // stretch
        m_stretcher.process(
                QAudioBufferDeinterleaveAdaptor<const float>{
                        wordConverted,
                },
                mediaFrameCount,
                QAudioBufferDeinterleaveAdaptor<float>{
                        timeStretcherOutput,
                },
                numberOfFullExpectedFrames);
 
        // convert to audio output format
        QAudioBuffer outputBuffer = m_toOutputFormatConverter->resample(
                timeStretcherOutput.constData<const char>(), timeStretcherOutput.byteCount());
 
        return outputBuffer;
    }
 
private:
    std::unique_ptr<QFFmpegResampler> m_toPCMDecoder;
    signalsmith::stretch::SignalsmithStretch<float> m_stretcher;
    std::unique_ptr<QFFmpegResampler> m_toOutputFormatConverter;
    float m_playbackRate;
    float m_pendingFractionalFrames = 0.f;
};
 
} // namespace
 
AbstractAudioFrameConverter::~AbstractAudioFrameConverter() = default;
 
std::unique_ptr<QFFmpegResampler> createResampler(const Frame &frame,
                                                  const QAudioFormat &outputFormat)
{
    return std::make_unique<QFFmpegResampler>(frame.codecContext(), outputFormat,
                                              frame.startTime().get());
}
 
std::unique_ptr<AbstractAudioFrameConverter>
makeTrivialAudioFrameConverter(const Frame &frame, QAudioFormat outputFormat, float playbackRate)
{
    return std::make_unique<TrivialAudioFrameConverter>(frame, outputFormat, playbackRate);
}
 
std::unique_ptr<AbstractAudioFrameConverter>
makePitchShiftingAudioFrameConverter(const Frame &frame, QAudioFormat outputFormat,
                                     float playbackRate)
{
    return std::make_unique<PitchShiftingAudioFrameConverter>(frame, outputFormat, playbackRate);
}
 
} // namespace QFFmpeg
 
QT_END_NAMESPACE