qgst_p.h

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// Copyright (C) 2016 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
 
#ifndef QGST_P_H
#define QGST_P_H
 
//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
 
#include <QtCore/qdebug.h>
#include <QtCore/qlist.h>
#include <QtCore/qmutex.h>
#include <QtCore/qsemaphore.h>
 
#include <QtMultimedia/qaudioformat.h>
#include <QtMultimedia/qvideoframe.h>
#include <QtMultimedia/private/qtmultimediaglobal_p.h>
#include <QtMultimedia/private/qmultimediautils_p.h>
#include <QtMultimedia/private/qplatformmediaplayer_p.h>
#include <QtMultimedia/private/qsharedhandle_p.h>
 
#include <gst/gst.h>
#include <gst/app/gstappsink.h>
#include <gst/app/gstappsrc.h>
#include <gst/video/video-info.h>
 
#if QT_CONFIG(gstreamer_gl_egl) && QT_CONFIG(linux_dmabuf)
#  define QT_GSTREAMER_SUPPORTS_GST_VIDEO_FORMAT_DMA_DRM GST_CHECK_VERSION(1, 24, 0)
#else
#  define QT_GSTREAMER_SUPPORTS_GST_VIDEO_FORMAT_DMA_DRM 0
#endif
 
#include "qgst_handle_types_p.h"
 
#include <type_traits>
#ifdef __cpp_lib_three_way_comparison
#  include <compare>
#endif
 
#if QT_CONFIG(gstreamer_photography)
#  define GST_USE_UNSTABLE_API
#  include <gst/interfaces/photography.h>
#  undef GST_USE_UNSTABLE_API
#endif
 
 
QT_BEGIN_NAMESPACE
 
namespace QGstImpl {
 
template <typename T>
struct GstObjectTraits
{
    // using Type = T;
    // template <typename U>
    // static bool isObjectOfType(U *);
    // template <typename U>
    // static T *cast(U *);
};
 
#define QGST_DEFINE_CAST_TRAITS(ClassName, MACRO_LABEL)
    template <>
    struct GstObjectTraits<ClassName>
    {
        using Type = ClassName;
        template <typename U>
        static bool isObjectOfType(U *arg)
        {
            return GST_IS_##MACRO_LABEL(arg);
        }
        template <typename U>
        static Type *cast(U *arg)
        {
            return GST_##MACRO_LABEL##_CAST(arg);
        }
        template <typename U>
        static Type *checked_cast(U *arg)
        {
            return GST_##MACRO_LABEL(arg);
        }
    };
    static_assert(true, "ensure semicolon")
 
#define QGST_DEFINE_CAST_TRAITS_FOR_INTERFACE(ClassName, MACRO_LABEL)
  template <>
  struct GstObjectTraits<ClassName>
  {
    using Type = ClassName;
    template <typename U>
    static bool isObjectOfType(U *arg)
    {
      return GST_IS_##MACRO_LABEL(arg);
    }
    template <typename U>
    static Type *cast(U *arg)
    {
      return checked_cast(arg);
    }
    template <typename U>
    static Type *checked_cast(U *arg)
    {
      return GST_##MACRO_LABEL(arg);
    }
  };
  static_assert(true, "ensure semicolon")
 
QGST_DEFINE_CAST_TRAITS(GstBin, BIN);
QGST_DEFINE_CAST_TRAITS(GstClock, CLOCK);
QGST_DEFINE_CAST_TRAITS(GstElement, ELEMENT);
QGST_DEFINE_CAST_TRAITS(GstObject, OBJECT);
QGST_DEFINE_CAST_TRAITS(GstPad, PAD);
QGST_DEFINE_CAST_TRAITS(GstPipeline, PIPELINE);
QGST_DEFINE_CAST_TRAITS(GstBaseSink, BASE_SINK);
QGST_DEFINE_CAST_TRAITS(GstBaseSrc, BASE_SRC);
QGST_DEFINE_CAST_TRAITS(GstAppSink, APP_SINK);
QGST_DEFINE_CAST_TRAITS(GstAppSrc, APP_SRC);
 
QGST_DEFINE_CAST_TRAITS_FOR_INTERFACE(GstTagSetter, TAG_SETTER);
 
 
template <>
struct GstObjectTraits<GObject>
{
    using Type = GObject;
    template <typename U>
    static bool isObjectOfType(U *arg)
    {
        return G_IS_OBJECT(arg);
    }
    template <typename U>
    static Type *cast(U *arg)
    {
        return G_OBJECT(arg);
    }
    template <typename U>
    static Type *checked_cast(U *arg)
    {
        return G_OBJECT(arg);
    }
};
 
#undef QGST_DEFINE_CAST_TRAITS
#undef QGST_DEFINE_CAST_TRAITS_FOR_INTERFACE
 
} // namespace QGstImpl
 
template <typename DestinationType, typename SourceType>
bool qIsGstObjectOfType(SourceType *arg)
{
    using Traits = QGstImpl::GstObjectTraits<DestinationType>;
    return arg && Traits::isObjectOfType(arg);
}
 
template <typename DestinationType, typename SourceType>
DestinationType *qGstSafeCast(SourceType *arg)
{
    using Traits = QGstImpl::GstObjectTraits<DestinationType>;
    if (arg && Traits::isObjectOfType(arg))
        return Traits::cast(arg);
    return nullptr;
}
 
template <typename DestinationType, typename SourceType>
DestinationType *qGstCheckedCast(SourceType *arg)
{
    using Traits = QGstImpl::GstObjectTraits<DestinationType>;
    if (arg)
        Q_ASSERT(Traits::isObjectOfType(arg));
    return Traits::cast(arg);
}
 
GstVideoFormat qGstVideoFormatFromPixelFormat(QVideoFrameFormat::PixelFormat format);
QVideoFrameFormat::PixelFormat qPixelFormatFromGstVideoFormat(GstVideoFormat format);
 
class QSize;
class QGstStructureView;
class QGstCaps;
class QCameraFormat;
 
struct QGstVideoInfo
{
    GstVideoInfo gstVideoInfo = {};
    std::optional<guint64> dmaDrmModifier;
};
 
template <typename T> struct QGRange
{
    T min;
    T max;
 
#ifdef __cpp_impl_three_way_comparison
    auto operator<=> (const QGRange &) const = default;
#else
    bool operator==(const QGRange &rhs) const
    {
        return std::tie(min, max) == std::tie(rhs.min, rhs.max);
    }
#endif
};
 
struct QGString : QUniqueGStringHandle
{
    using QUniqueGStringHandle::QUniqueGStringHandle;
 
    QLatin1StringView asStringView() const { return QLatin1StringView{ get() }; }
    QByteArrayView asByteArrayView() const { return QByteArrayView{ get() }; }
    QString toQString() const { return QString::fromUtf8(get()); }
 
#ifdef __cpp_lib_three_way_comparison
    // clang-format off
    friend auto operator<=>(const QGString &lhs, const QGString &rhs)
    {
        return lhs.asStringView() <=> rhs.asStringView();
    }
    friend auto operator<=>(const QGString &lhs, const QLatin1StringView rhs)
    {
        return lhs.asStringView() <=> rhs;
    }
    friend auto operator<=>(const QGString &lhs, const QByteArrayView rhs)
    {
        return lhs.asByteArrayView() <=> rhs;
    }
    friend auto operator<=>(const QLatin1StringView lhs, const QGString &rhs)
    {
        return lhs <=> rhs.asStringView();
    }
    friend auto operator<=>(const QByteArrayView lhs, const QGString &rhs)
    {
        return lhs <=> rhs.asByteArrayView();
    }
    // clang-format on
#else
    // remove once we're on c++20
    bool operator==(const QGString &str) const { return asStringView() == str.asStringView(); }
    bool operator==(const QLatin1StringView str) const { return asStringView() == str; }
    bool operator==(const QByteArrayView str) const { return asByteArrayView() == str; }
 
    bool operator!=(const QGString &str) const { return asStringView() != str.asStringView(); }
    bool operator!=(const QLatin1StringView str) const { return asStringView() != str; }
    bool operator!=(const QByteArrayView str) const { return asByteArrayView() != str; }
 
    friend bool operator<(const QGString &lhs, const QGString &rhs)
    {
        return lhs.asStringView() < rhs.asStringView();
    }
    friend bool operator<(const QGString &lhs, const QLatin1StringView rhs)
    {
        return lhs.asStringView() < rhs;
    }
    friend bool operator<(const QGString &lhs, const QByteArrayView rhs)
    {
        return lhs.asByteArrayView() < rhs;
    }
    friend bool operator<(const QLatin1StringView lhs, const QGString &rhs)
    {
        return lhs < rhs.asStringView();
    }
    friend bool operator<(const QByteArrayView lhs, const QGString &rhs)
    {
        return lhs < rhs.asByteArrayView();
    }
#endif
 
    explicit operator QByteArrayView() const { return asByteArrayView(); }
    explicit operator QByteArray() const { return QByteArray{ asByteArrayView() }; }
};
 
class QGValue
{
public:
    explicit QGValue(const GValue *v);
    const GValue *value;
 
    bool isNull() const;
 
    std::optional<bool> toBool() const;
    std::optional<int> toInt() const;
    std::optional<int> toInt64() const;
    template<typename T>
    T *getPointer() const
    {
        return value ? static_cast<T *>(g_value_get_pointer(value)) : nullptr;
    }
 
    const char *toString() const;
    std::optional<float> getFraction() const;
    std::optional<QGRange<float>> getFractionRange() const;
    std::optional<QGRange<int>> toIntRange() const;
 
    QGstStructureView toStructure() const;
    QGstCaps toCaps() const;
 
    bool isList() const;
    int listSize() const;
    QGValue at(int index) const;
 
    QList<QAudioFormat::SampleFormat> getSampleFormats() const;
};
 
class QGstreamerMessage;
 
class QGstStructureView
{
public:
    const GstStructure *structure = nullptr;
    explicit QGstStructureView(const GstStructure *);
    explicit QGstStructureView(const QUniqueGstStructureHandle &);
 
    QUniqueGstStructureHandle clone() const;
 
    bool isNull() const;
    QByteArrayView name() const;
    QGValue operator[](const char *fieldname) const;
 
    QGstCaps caps() const;
    QGstTagListHandle tags() const;
 
    QSize resolution() const;
    QList<QVideoFrameFormat::PixelFormat> pixelFormats() const;
    QGRange<float> frameRateRange() const;
    std::optional<QGRange<QSize>> resolutionRange() const;
    QGstreamerMessage getMessage();
    std::optional<Fraction> pixelAspectRatio() const;
    QSize nativeSize() const;
};
 
struct QSharedGstCapsTraits
{
    using Type = GstCaps *;
    static constexpr Type invalidValue() noexcept { return nullptr; }
    static GstCaps *ref(GstCaps *arg) noexcept { return gst_caps_ref(arg); }
    static bool unref(GstCaps *arg) noexcept
    {
        gst_caps_unref(arg);
        return true;
    }
};
 
class QGstCaps : public QtPrivate::QSharedHandle<QSharedGstCapsTraits>
{
    using BaseClass = QtPrivate::QSharedHandle<QSharedGstCapsTraits>;
 
public:
    using BaseClass::BaseClass;
    QGstCaps(const QGstCaps &) = default;
    QGstCaps(QGstCaps &&) noexcept = default;
    QGstCaps &operator=(const QGstCaps &) = default;
    QGstCaps &operator=(QGstCaps &&) noexcept = default;
 
    enum MemoryFormat { CpuMemory, GLTexture, DMABuf };
 
    int size() const;
    QGstStructureView at(int index) const;
    GstCaps *caps() const;
 
    MemoryFormat memoryFormat() const;
    std::optional<QGstVideoInfo> videoInfo() const;
 
    void addPixelFormats(const QList<QVideoFrameFormat::PixelFormat> &formats,
                         const char* capsFeatures = nullptr);
    void setResolution(QSize);
 
    static QGstCaps create();
 
    static QGstCaps fromCameraFormat(const QCameraFormat &format);
 
    QGstCaps copy() const;
};
 
struct QSharedGstObjectTraits
{
    using Type = GstObject *;
    static constexpr Type invalidValue() noexcept { return nullptr; }
    static GstObject *ref(GstObject *arg) noexcept
    {
        gst_object_ref_sink(arg);
        return arg;
    }
    static bool unref(GstObject *arg) noexcept
    {
        gst_object_unref(arg);
        return true;
    }
};
 
class QGObjectHandlerConnection;
 
class QGstObject : public QtPrivate::QSharedHandle<QSharedGstObjectTraits>
{
    using BaseClass = QtPrivate::QSharedHandle<QSharedGstObjectTraits>;
 
public:
    using BaseClass::BaseClass;
    QGstObject(const QGstObject &) = default;
    QGstObject(QGstObject &&) noexcept = default;
 
    QGstObject &operator=(const QGstObject &) = default;
    QGstObject &operator=(QGstObject &&) noexcept = default;
 
    void set(const char *property, const char *str);
    void set(const char *property, bool b);
    void set(const char *property, int32_t i);
    void set(const char *property, uint32_t i);
    void set(const char *property, int64_t i);
    void set(const char *property, uint64_t i);
    void set(const char *property, double d);
    void set(const char *property, const QGstObject &o);
    void set(const char *property, const QGstCaps &c);
    void set(const char *property, void *object, GDestroyNotify destroyFunction);
 
    template <typename Object>
    void set(const char *property, Object *object, GDestroyNotify destroyFunction)
    {
        set(property, static_cast<void *>(object), destroyFunction);
    }
 
    template <typename Object>
    void set(const char *property, std::unique_ptr<Object> object)
    {
        set(property, static_cast<void *>(object.release()), qDeleteFromVoidPointer<Object>);
    }
 
    template <typename T>
    static void qDeleteFromVoidPointer(void *ptr)
    {
        delete reinterpret_cast<T *>(ptr);
    }
 
    QGString getString(const char *property) const;
    QGstStructureView getStructure(const char *property) const;
    bool getBool(const char *property) const;
    uint getUInt(const char *property) const;
    int getInt(const char *property) const;
    quint64 getUInt64(const char *property) const;
    qint64 getInt64(const char *property) const;
    float getFloat(const char *property) const;
    double getDouble(const char *property) const;
    QGstObject getGstObject(const char *property) const;
    void *getObject(const char *property) const;
 
    template <typename T>
    T *getObject(const char *property) const
    {
        void *rawObject = getObject(property);
        return reinterpret_cast<T *>(rawObject);
    }
 
    QGObjectHandlerConnection connect(const char *name, GCallback callback, gpointer userData);
    void disconnect(gulong handlerId);
 
    GType type() const;
    QLatin1StringView typeName() const;
    GstObject *object() const;
    QLatin1StringView name() const;
};
 
class QGObjectHandlerConnection
{
public:
    QGObjectHandlerConnection(QGstObject object, gulong handler);
 
    QGObjectHandlerConnection() = default;
    QGObjectHandlerConnection(const QGObjectHandlerConnection &) = default;
    QGObjectHandlerConnection(QGObjectHandlerConnection &&) = default;
    QGObjectHandlerConnection &operator=(const QGObjectHandlerConnection &) = default;
    QGObjectHandlerConnection &operator=(QGObjectHandlerConnection &&) = default;
 
    void disconnect();
 
private:
    static constexpr gulong invalidHandlerId = std::numeric_limits<gulong>::max();
 
    QGstObject object;
    gulong handlerId = invalidHandlerId;
};
 
// disconnects in dtor
class QGObjectHandlerScopedConnection
{
public:
    QGObjectHandlerScopedConnection(QGObjectHandlerConnection connection);
 
    QGObjectHandlerScopedConnection() = default;
    QGObjectHandlerScopedConnection(const QGObjectHandlerScopedConnection &) = delete;
    QGObjectHandlerScopedConnection &operator=(const QGObjectHandlerScopedConnection &) = delete;
    QGObjectHandlerScopedConnection(QGObjectHandlerScopedConnection &&) = default;
    QGObjectHandlerScopedConnection &operator=(QGObjectHandlerScopedConnection &&) = default;
 
    ~QGObjectHandlerScopedConnection();
 
    void disconnect();
 
private:
    QGObjectHandlerConnection connection;
};
 
class QGstElement;
 
class QGstPad : public QGstObject
{
public:
    using QGstObject::QGstObject;
    QGstPad(const QGstPad &) = default;
    QGstPad(QGstPad &&) noexcept = default;
 
    explicit QGstPad(const QGstObject &o);
    explicit QGstPad(GstPad *pad, RefMode mode);
 
    QGstPad &operator=(const QGstPad &) = default;
    QGstPad &operator=(QGstPad &&) noexcept = default;
 
    QGstCaps currentCaps() const;
    QGstCaps queryCaps() const;
 
    QGstTagListHandle tags() const;
    QGString streamId() const;
 
    std::optional<QPlatformMediaPlayer::TrackType>
    inferTrackTypeFromName() const; // for decodebin3 etc
 
    bool isLinked() const;
    bool link(const QGstPad &sink) const;
    bool unlink(const QGstPad &sink) const;
    bool unlinkPeer() const;
    QGstPad peer() const;
    QGstElement parent() const;
 
    GstPad *pad() const;
 
    GstEvent *stickyEvent(GstEventType type);
    bool sendEvent(GstEvent *event);
    void sendFlushStartStop(bool resetTime);
 
    template <auto Member, typename T>
    void addProbe(T *instance, GstPadProbeType type);
 
    template <typename Functor>
    void doInIdleProbe(Functor &&work);
 
    template <auto Member, typename T>
    void addEosProbe(T *instance);
 
    template <typename Functor>
    void modifyPipelineInIdleProbe(Functor &&f);
 
    void sendFlushIfPaused();
};
 
class QGstClock : public QGstObject
{
public:
    QGstClock() = default;
    explicit QGstClock(const QGstObject &o);
    explicit QGstClock(GstClock *clock, RefMode mode);
 
    GstClock *clock() const;
    GstClockTime time() const;
};
 
class QGstBin;
class QGstPipeline;
 
class QGstElement : public QGstObject
{
public:
    using QGstObject::QGstObject;
 
    QGstElement(const QGstElement &) = default;
    QGstElement(QGstElement &&) noexcept = default;
    QGstElement &operator=(const QGstElement &) = default;
    QGstElement &operator=(QGstElement &&) noexcept = default;
 
    explicit QGstElement(GstElement *element, RefMode mode);
    static QGstElement createFromFactory(const char *factory, const char *name = nullptr);
    static QGstElement createFromFactory(GstElementFactory *, const char *name = nullptr);
    static QGstElement createFromFactory(const QGstElementFactoryHandle &,
                                         const char *name = nullptr);
    static QGstElement createFromDevice(const QGstDeviceHandle &, const char *name = nullptr);
    static QGstElement createFromDevice(GstDevice *, const char *name = nullptr);
    static QGstElement createFromPipelineDescription(const char *);
    static QGstElement createFromPipelineDescription(const QByteArray &);
 
    static QGstElementFactoryHandle findFactory(const char *);
    static QGstElementFactoryHandle findFactory(const QByteArray &name);
 
    QByteArrayView factoryName() const;
 
    QGstPad staticPad(const char *name) const;
    QGstPad src() const;
    QGstPad sink() const;
    QGstPad getRequestPad(const char *name) const;
    void releaseRequestPad(const QGstPad &pad) const;
 
    GstState state(std::chrono::nanoseconds timeout = std::chrono::seconds(0)) const;
    GstStateChangeReturn setState(GstState state);
    bool setStateSync(GstState state, std::chrono::nanoseconds timeout = std::chrono::seconds(1));
    bool syncStateWithParent();
    bool finishStateChange(std::chrono::nanoseconds timeout = std::chrono::seconds(5));
    bool hasAsyncStateChange(std::chrono::nanoseconds timeout = std::chrono::seconds(0)) const;
    bool waitForAsyncStateChangeComplete(
            std::chrono::nanoseconds timeout = std::chrono::seconds(5)) const;
 
    void lockState(bool locked);
    bool isStateLocked() const;
 
    void sendEvent(GstEvent *event) const;
    void sendEos() const;
 
    std::optional<std::chrono::nanoseconds> duration() const;
    std::optional<std::chrono::milliseconds> durationInMs() const;
    std::optional<std::chrono::nanoseconds> position() const;
    std::optional<std::chrono::milliseconds> positionInMs() const;
    std::optional<bool> canSeek() const;
 
    template <auto Member, typename T>
    QGObjectHandlerConnection onPadAdded(T *instance)
    {
        struct Impl
        {
            static void callback(GstElement *e, GstPad *pad, gpointer userData)
            {
                (static_cast<T *>(userData)->*Member)(QGstElement(e, NeedsRef),
                                                      QGstPad(pad, NeedsRef));
            };
        };
 
        return connect("pad-added", G_CALLBACK(Impl::callback), instance);
    }
    template <auto Member, typename T>
    QGObjectHandlerConnection onPadRemoved(T *instance)
    {
        struct Impl
        {
            static void callback(GstElement *e, GstPad *pad, gpointer userData)
            {
                (static_cast<T *>(userData)->*Member)(QGstElement(e, NeedsRef),
                                                      QGstPad(pad, NeedsRef));
            };
        };
 
        return connect("pad-removed", G_CALLBACK(Impl::callback), instance);
    }
    template <auto Member, typename T>
    QGObjectHandlerConnection onNoMorePads(T *instance)
    {
        struct Impl
        {
            static void callback(GstElement *e, gpointer userData)
            {
                (static_cast<T *>(userData)->*Member)(QGstElement(e, NeedsRef));
            };
        };
 
        return connect("no-more-pads", G_CALLBACK(Impl::callback), instance);
    }
 
    GstClockTime baseTime() const;
    void setBaseTime(GstClockTime time) const;
 
    GstElement *element() const;
 
    QGstElement getParent() const;
    QGstBin getParentBin() const;
    QGstPipeline getPipeline() const;
    QGstBin getRootBin() const;
 
    void removeFromParent();
    void dumpPipelineGraph(const char *filename) const;
 
private:
    QGstQueryHandle &positionQuery() const;
    mutable QGstQueryHandle m_positionQuery;
};
 
// QGstPad implementations
 
template <auto Member, typename T>
void QGstPad::addProbe(T *instance, GstPadProbeType type)
{
    auto callback = [](GstPad *pad, GstPadProbeInfo *info, gpointer userData) {
        return (static_cast<T *>(userData)->*Member)(QGstPad(pad, NeedsRef), info);
    };
 
    gst_pad_add_probe(pad(), type, callback, instance, nullptr);
}
 
template <typename Functor>
void QGstPad::doInIdleProbe(Functor &&work)
{
    using namespace std::chrono_literals;
 
    struct CallbackData
    {
        QSemaphore waitDone;
        std::once_flag onceFlag;
        Functor work;
 
        void run()
        {
            std::call_once(onceFlag, [&] {
                work();
            });
        }
    };
 
    CallbackData cd{ QSemaphore{}, {}, std::forward<Functor>(work) };
 
    auto callback = [](GstPad *, GstPadProbeInfo *, gpointer p) {
        auto cd = reinterpret_cast<CallbackData *>(p);
        cd->run();
        cd->waitDone.release();
        return GST_PAD_PROBE_REMOVE;
    };
 
    gulong probe = gst_pad_add_probe(pad(), GST_PAD_PROBE_TYPE_IDLE, callback, &cd, nullptr);
    if (probe == 0)
        return; // probe was executed
 
    bool success = cd.waitDone.try_acquire_for(250ms);
    if (success)
        return;
 
    // the probe has not been executed for 250ms, probably because the element has transitioned
    // from playing to paused. Flushing the pad would unblock paused pads
    sendFlushIfPaused();
 
    success = cd.waitDone.try_acquire_for(1s);
    if (success)
        return;
 
    // if the idle probe still has not been called, we remove it and call it
    // explicitly to avoid deadlocking the application. Probably not exactly safe,
    // but better than deadlocking
    qWarning() << "QGstPad::doInIdleProbe blocked for 1s. Executing the pad probe manually";
    parent().dumpPipelineGraph("doInIdleProbeHang");
    gst_pad_remove_probe(pad(), probe);
    cd.run();
}
 
template <auto Member, typename T>
void QGstPad::addEosProbe(T *instance)
{
    auto callback = [](GstPad *, GstPadProbeInfo *info, gpointer userData) {
        if (GST_EVENT_TYPE(GST_PAD_PROBE_INFO_DATA(info)) != GST_EVENT_EOS)
            return GST_PAD_PROBE_PASS;
        (static_cast<T *>(userData)->*Member)();
        return GST_PAD_PROBE_REMOVE;
    };
 
    gst_pad_add_probe(pad(), GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM, callback, instance, nullptr);
}
template <typename Functor>
void QGstPad::modifyPipelineInIdleProbe(Functor &&f)
{
    using namespace std::chrono_literals;
 
    GstPadDirection direction = gst_pad_get_direction(pad());
 
    switch (direction) {
    case GstPadDirection::GST_PAD_SINK: {
        // modifying a source: we need to flush the sink pad before we can modify downstream
        // elements
        sendFlushIfPaused();
        doInIdleProbe(f);
        return;
    }
    case GstPadDirection::GST_PAD_SRC: {
        // modifying a sink: we need to use the idle probes iff the pipeline is playing
        if (parent().state(1s) == GstState::GST_STATE_PLAYING)
            doInIdleProbe(f);
        else
            f();
        return;
    }
 
    default:
        Q_UNREACHABLE();
    }
}
 
template <typename... Ts>
std::enable_if_t<(std::is_base_of_v<QGstElement, Ts> && ...), void>
qLinkGstElements(const Ts &...ts)
{
    bool link_success = [&] {
        if constexpr (sizeof...(Ts) == 2)
            return gst_element_link(ts.element()...);
        else
            return gst_element_link_many(ts.element()..., nullptr);
    }();
 
    if (Q_UNLIKELY(!link_success)) {
        qWarning() << "qLinkGstElements: could not link elements: "
                   << std::initializer_list<const char *>{
                          (GST_ELEMENT_NAME(ts.element()))...,
                      };
    }
}
 
template <typename... Ts>
std::enable_if_t<(std::is_base_of_v<QGstElement, Ts> && ...), void>
qUnlinkGstElements(const Ts &...ts)
{
    if constexpr (sizeof...(Ts) == 2)
        gst_element_unlink(ts.element()...);
    else
        gst_element_unlink_many(ts.element()..., nullptr);
}
 
class QGstBin : public QGstElement
{
public:
    using QGstElement::QGstElement;
    QGstBin(const QGstBin &) = default;
    QGstBin(QGstBin &&) noexcept = default;
    QGstBin &operator=(const QGstBin &) = default;
    QGstBin &operator=(QGstBin &&) noexcept = default;
 
    explicit QGstBin(GstBin *bin, RefMode mode = NeedsRef);
    static QGstBin create(const char *name);
    static QGstBin createFromFactory(const char *factory, const char *name);
    static QGstBin createFromPipelineDescription(const QByteArray &pipelineDescription,
                                                 const char *name = nullptr,
                                                 bool ghostUnlinkedPads = false);
    static QGstBin createFromPipelineDescription(const char *pipelineDescription,
                                                 const char *name = nullptr,
                                                 bool ghostUnlinkedPads = false);
 
    template <typename... Ts>
    std::enable_if_t<(std::is_base_of_v<QGstElement, Ts> && ...), void> add(const Ts &...ts)
    {
        if constexpr (sizeof...(Ts) == 1)
            gst_bin_add(bin(), ts.element()...);
        else
            gst_bin_add_many(bin(), ts.element()..., nullptr);
    }
 
    template <typename... Ts>
    std::enable_if_t<(std::is_base_of_v<QGstElement, Ts> && ...), void> remove(const Ts &...ts)
    {
        if constexpr (sizeof...(Ts) == 1)
            gst_bin_remove(bin(), ts.element()...);
        else
            gst_bin_remove_many(bin(), ts.element()..., nullptr);
    }
 
    template <typename... Ts>
    std::enable_if_t<(std::is_base_of_v<QGstElement, std::remove_reference_t<Ts>> && ...), void>
    stopAndRemoveElements(Ts &&...ts)
    {
        bool stateChangeSuccessful = (ts.setStateSync(GST_STATE_NULL) && ...);
        Q_ASSERT(stateChangeSuccessful);
        remove(ts...);
    }
 
    GstBin *bin() const;
 
    void addGhostPad(const QGstElement &child, const char *name);
    void addGhostPad(const char *name, const QGstPad &pad);
    void addUnlinkedGhostPads(GstPadDirection);
 
    bool syncChildrenState();
 
    void dumpGraph(const char *fileNamePrefix, bool includeTimestamp = true) const;
 
    QGstElement findByName(const char *);
 
    void recalculateLatency();
};
 
class QGstBaseSink : public QGstElement
{
public:
    using QGstElement::QGstElement;
 
    explicit QGstBaseSink(GstBaseSink *, RefMode);
 
    QGstBaseSink(const QGstBaseSink &) = default;
    QGstBaseSink(QGstBaseSink &&) noexcept = default;
    QGstBaseSink &operator=(const QGstBaseSink &) = default;
    QGstBaseSink &operator=(QGstBaseSink &&) noexcept = default;
 
    void setSync(bool);
 
    GstBaseSink *baseSink() const;
};
 
class QGstBaseSrc : public QGstElement
{
public:
    using QGstElement::QGstElement;
 
    explicit QGstBaseSrc(GstBaseSrc *, RefMode);
 
    QGstBaseSrc(const QGstBaseSrc &) = default;
    QGstBaseSrc(QGstBaseSrc &&) noexcept = default;
    QGstBaseSrc &operator=(const QGstBaseSrc &) = default;
    QGstBaseSrc &operator=(QGstBaseSrc &&) noexcept = default;
 
    GstBaseSrc *baseSrc() const;
};
 
class QGstAppSink : public QGstBaseSink
{
public:
    using QGstBaseSink::QGstBaseSink;
 
    explicit QGstAppSink(GstAppSink *, RefMode);
 
    QGstAppSink(const QGstAppSink &) = default;
    QGstAppSink(QGstAppSink &&) noexcept = default;
    QGstAppSink &operator=(const QGstAppSink &) = default;
    QGstAppSink &operator=(QGstAppSink &&) noexcept = default;
 
    static QGstAppSink create(const char *name);
 
    GstAppSink *appSink() const;
 
    void setMaxBuffers(int);
#  if GST_CHECK_VERSION(1, 24, 0)
    void setMaxBufferTime(std::chrono::nanoseconds);
#  endif
 
    void setCaps(const QGstCaps &caps);
    void setCallbacks(GstAppSinkCallbacks &callbacks, gpointer user_data, GDestroyNotify notify);
 
    QGstSampleHandle pullSample();
};
 
class QGstAppSrc : public QGstBaseSrc
{
public:
    using QGstBaseSrc::QGstBaseSrc;
 
    explicit QGstAppSrc(GstAppSrc *, RefMode);
 
    QGstAppSrc(const QGstAppSrc &) = default;
    QGstAppSrc(QGstAppSrc &&) noexcept = default;
    QGstAppSrc &operator=(const QGstAppSrc &) = default;
    QGstAppSrc &operator=(QGstAppSrc &&) noexcept = default;
 
    static QGstAppSrc create(const char *name);
 
    GstAppSrc *appSrc() const;
 
    void setCallbacks(GstAppSrcCallbacks &callbacks, gpointer user_data, GDestroyNotify notify);
 
    GstFlowReturn pushBuffer(GstBuffer *); // take ownership
};
 
inline GstClockTime qGstClockTimeFromChrono(std::chrono::nanoseconds ns)
{
    return ns.count();
}
 
QString qGstErrorMessageCannotFindElement(std::string_view element);
 
template <typename Arg, typename... Args>
std::optional<QString> qGstErrorMessageIfElementsNotAvailable(const Arg &arg, Args... args)
{
    QGstElementFactoryHandle factory = QGstElement::findFactory(arg);
    if (!factory)
        return qGstErrorMessageCannotFindElement(arg);
 
    if constexpr (sizeof...(args) != 0)
        return qGstErrorMessageIfElementsNotAvailable(args...);
    else
        return std::nullopt;
}
 
template <typename Functor>
void qForeachStreamInCollection(GstStreamCollection *collection, Functor &&f)
{
    guint size = gst_stream_collection_get_size(collection);
    for (guint index = 0; index != size; ++index)
        f(gst_stream_collection_get_stream(collection, index));
}
 
template <typename Functor>
void qForeachStreamInCollection(const QGstStreamCollectionHandle &collection, Functor &&f)
{
    qForeachStreamInCollection(collection.get(), std::forward<Functor>(f));
}
 
QVideoFrameFormat qVideoFrameFormatFromGstVideoInfo(const QGstVideoInfo &vidInfo);
QGstCaps::MemoryFormat qMemoryFormatFromGstBuffer(GstBuffer *buffer);
QVideoFrame qCreateFrameFromGstBuffer(QGstBufferHandle buffer, const QGstVideoInfo &videoInfo);
 
QT_END_NAMESPACE
 
namespace std {
 
template <>
struct hash<QT_PREPEND_NAMESPACE(QGstElement)>
{
    using argument_type = QT_PREPEND_NAMESPACE(QGstElement);
    using result_type = size_t;
    result_type operator()(const argument_type &e) const noexcept
    {
        return std::hash<void *>{}(e.element());
    }
};
} // namespace std
 
#endif