libVLC 视频抓图

Windows操作系统提供了多种便捷的截图方式，常见的有以下几种：

• 全屏截图：通过按下PrtSc键（Print Screen），可以截取整个屏幕的内容。截取的图像会保存在剪贴板中，可以通过Ctrl+V粘贴到图片编辑工具或其他软件的输入框中。
• 当前窗口截图：同时按下Alt + PrtSc键，可以截取当前活动的窗口。同样，截图内容会被保存在剪贴板中。
• 矩形截图：使用快捷键Windows + Shift + S，可以选择矩形截图模式，然后拖动鼠标选取屏幕上的任意矩形区域进行截图。
• 自由形状截图：同样使用Windows + Shift + S快捷键，可以选择任意形状截图模式，允许你自由绘制截图区域的形状。

libVLC 中通过libvlc_video_take_snapshot核心接口来截图。

以下是如何使用 libVLC 设置视频裁剪区域的基本步骤：

1. 初始化 libVLC 和媒体播放器

首先，你需要初始化 libVLC 实例和媒体播放器对象。

#include <vlc/vlc.h>
 
int main(int argc, char* argv[])
{
    libvlc_instance_t* inst;
    libvlc_media_player_t* mp;
    libvlc_media_t* m;
 
    // 加载 libVLC 引擎
    inst = libvlc_new(0, NULL);
 
    // 创建一个新的 item
    m = libvlc_media_new_location(inst, "your_video_path_here");
    mp = libvlc_media_player_new_from_media(m);
 
    // 不再需要媒体对象
    libvlc_media_release(m);
}

2. 播放视频

// 播放媒体播放器
libvlc_media_player_play(mp);
 
// 保持程序运行，直到视频播放完成
while (libvlc_media_player_is_playing(mp)) {
    // 可以在这里加入延时
}
 
// 清理 libVLC
libvlc_media_player_stop(mp);
libvlc_media_player_release(mp);
libvlc_release(inst);
 
return 0;

3.截图

这里为了方便，路径写死了。

	if (vlc_mediaPlayer)
	{
		QString path = "./snap.png";
		libvlc_video_take_snapshot(vlc_mediaPlayer, 0, path.toUtf8().data(), 0, 0);
	}

以下是VLC播放器中使用的截图界面，我们仿照这个做一个界面。 

以下是效果图。

菜单添加action，并响应槽函数。

m_snapAction = m_videoMenu->addAction("截图");
connect(m_snapAction, &QAction::triggered, this, &showWidget::slotSnap);

槽函数如下图所示，为了方便，路径写死了。 

void showWidget::slotSnap()
{
	if (vlc_mediaPlayer)
	{
		QString path = "./snap.png";
		libvlc_video_take_snapshot(vlc_mediaPlayer, 0, path.toUtf8().data(), 0, 0);
	}
}

生成目录下snap.png。 

完整源码：

#pragma once
#define LIBVLC_USE_PTHREAD_CANCEL 1
#include <QtWidgets/QWidget>
#include "ui_showWidget.h"
#include <QMenu>
#include <QActionGroup>
#include <vlc/vlc.h>
 
#include <QDebug>
#include <QFileDialog>
#include <QThread>
#include <QMouseEvent>
#include <QKeyEvent>
 
enum Rate
{
	Rate2X,
	Rate1_5X,
	Rate1_25X,
	Rate1_0X,
	Rate0_75X,
	Rate0_5X
};
 
class showWidget : public QWidget
{
    Q_OBJECT
 
public:
    showWidget(QWidget *parent = nullptr);
    ~showWidget();
 
protected:
	virtual void mousePressEvent(QMouseEvent *event);
	virtual void mouseDoubleClickEvent(QMouseEvent *event);
	virtual void keyPressEvent(QKeyEvent *event);
 
private slots:
	void slotOpenFile();
	void slotPlay();
	void slotPause();
	void slotStop();
	void slotValueChanged(int value);
	void slotCurrentIndexChanged(int index);
	void slotActionTriggered(QAction *action);
	void slotCropActionTriggered(QAction *action);
	void slotScaleActionTriggered(QAction *action);
 
	void slotSnap();
 
private:
	//事件处理回调
	static void vlcEvents(const libvlc_event_t *ev, void *param);
 
	//初始化menu
	void initMenu();
 
private:
    Ui::showWidgetClass ui;
 
private:
	libvlc_instance_t *vlc_base = nullptr;
	libvlc_media_t *vlc_media = nullptr;
	libvlc_media_player_t *vlc_mediaPlayer = nullptr;
 
	QList<float> m_lstRate;
 
	QMenu *m_menu = nullptr;
	QAction *m_video = nullptr;
 
	QAction *m_scaleAction = nullptr;	//缩放
	QAction *m_aspectRatioAction = nullptr;	//宽高比
	QAction *m_cropAction = nullptr;	//裁剪
	QAction *m_snapAction = nullptr;//截图
 
	QMenu *m_videoMenu = nullptr;
 
	//宽高比
	QMenu *m_aspectRatioMenu = nullptr;
	QAction *m_default = nullptr;
	QAction *m_16_9 = nullptr;
	QAction *m_4_3 = nullptr;
	QAction *m_1_1 = nullptr;
	QAction *m_16_10 = nullptr;
	QAction *m_2_21_1 = nullptr;
	QAction *m_2_35_1= nullptr;
	QAction *m_2_38_1 = nullptr;
	QAction *m_5_4 = nullptr;
 
	QActionGroup *m_group = nullptr;
	QAction *m_preAspectRatio = nullptr;
	//宽高比
	//裁剪
	QMenu *m_cropMenu = nullptr;
	QAction *m__cropDefault = nullptr;
	QAction *m__crop16_10 = nullptr;
	QAction *m__crop16_9 = nullptr;
	QAction *m__crop4_3 = nullptr;
	QAction *m__crop1_85_1 = nullptr;
	QAction *m__crop2_21_1 = nullptr;
	QAction *m__crop2_35_1 = nullptr;
	QAction *m__crop2_39_1 = nullptr;
	QAction *m__crop5_3 = nullptr;
	QAction *m__crop5_4 = nullptr;
	QAction *m__crop1_1 = nullptr;
 
	QActionGroup *m_cropGroup = nullptr;
	QAction *m_preCrop= nullptr;
	//裁剪
 
	//缩放
	QMenu *m_scaleMenu = nullptr;
	QAction *m_scale1_4 = nullptr;
	QAction *m_scale1_2 = nullptr;
	QAction *m_scale1_1 = nullptr;
	QAction *m_scale2_1 = nullptr;
 
	QActionGroup *m_scaleGroup = nullptr;
	QAction *m_preScale = nullptr;
	//缩放
 
	char *m_defalutRate = nullptr;
	char *m_defalutCrop = nullptr;
	float m_defalutScale = 0;
};

cpp

#include "showWidget.h"
#include <QTimer>
#include <QTime>
 
#pragma execution_character_set("utf-8")
 
showWidget::showWidget(QWidget *parent)
    : QWidget(parent)
{
    ui.setupUi(this);
 
	this->setWindowTitle("视频播放器");
 
	ui.cbxRate->setCurrentIndex(Rate1_0X);
 
	m_lstRate << 2.0 << 1.5 << 1.25 << 1.0 << 0.75 << 0.5;
 
	initMenu();
 
	ui.btnOpen->setFocusPolicy(Qt::NoFocus);
	ui.btnPlay->setFocusPolicy(Qt::NoFocus);
	ui.btnPause->setFocusPolicy(Qt::NoFocus);
	ui.btnStop->setFocusPolicy(Qt::NoFocus);
	ui.hSliderVolumn->setFocusPolicy(Qt::NoFocus);
	ui.cbxRate->setFocusPolicy(Qt::NoFocus);
 
	connect(ui.btnOpen, &QPushButton::clicked, this, &showWidget::slotOpenFile);
	connect(ui.btnPlay, &QPushButton::clicked, this, &showWidget::slotPlay);
	connect(ui.btnPause, &QPushButton::clicked, this, &showWidget::slotPause);
	connect(ui.btnStop, &QPushButton::clicked, this, &showWidget::slotStop);
	connect(ui.btnSnap, &QPushButton::clicked, this, &showWidget::slotSnap);
	connect(ui.hSliderVolumn, &QSlider::valueChanged, this, &showWidget::slotValueChanged);
	connect(ui.cbxRate,SIGNAL(currentIndexChanged(int)), this, SLOT(slotCurrentIndexChanged(int)));
}
 
showWidget::~showWidget()
{
	libvlc_release(vlc_base); //减少libvlc实例的引用计数，并销毁
}
 
void showWidget::mousePressEvent(QMouseEvent *event)
{
	switch (event->button())
	{
	case Qt::RightButton:
		//this->setWindowState(Qt::WindowMinimized);
		m_menu->exec(event->globalPos());
		break;
	default:
		QWidget::mousePressEvent(event);
	}
}
 
void showWidget::mouseDoubleClickEvent(QMouseEvent *event)
{
	if (this->isFullScreen())
	{
		this->showNormal();
	}
	else
	{
		this->showFullScreen();
	}
}
 
void showWidget::keyPressEvent(QKeyEvent *event)
{
	if (!vlc_mediaPlayer)
		return;
 
	int value = ui.hSliderVolumn->value();
	if (event->key() == Qt::Key_W)	//添加音量
	{
		qDebug() << "up";
		slotValueChanged(value+10);
	}
	else if (event->key() == Qt::Key_S)	//减小音量
	{
		slotValueChanged(value - 10);
	}
	else if (event->key() == Qt::Key_Space)
	{
		if (vlc_mediaPlayer && libvlc_media_player_get_state(vlc_mediaPlayer) == libvlc_Playing)
		{
			libvlc_media_player_pause(vlc_mediaPlayer);
		}
		else if (vlc_mediaPlayer && libvlc_media_player_get_state(vlc_mediaPlayer) == libvlc_Paused)
		{
			libvlc_media_player_play(vlc_mediaPlayer);
		}
	}
}
 
void showWidget::slotOpenFile()
{
	/*选择文件*/
	QString filename = QFileDialog::getOpenFileName(this, "选择打开的文件", "D:/", tr("*.*"));
	std::replace(filename.begin(), filename.end(), QChar('/'), QChar('\\'));
	vlc_base = libvlc_new(0, NULL);
	vlc_media = libvlc_media_new_path(vlc_base, filename.toUtf8().data());
	if (!vlc_media) {
		return;
	}
 
	// 创建libvlc实例和媒体播放器
	vlc_mediaPlayer = libvlc_media_player_new_from_media(vlc_media);
	if (!vlc_mediaPlayer) {
		return;
	}
	
	// 等待元数据加载完成
	libvlc_media_parse(vlc_media);
 
	m_defalutRate = libvlc_video_get_aspect_ratio(vlc_mediaPlayer);
	m_defalutCrop = libvlc_video_get_crop_geometry(vlc_mediaPlayer);
 
	libvlc_video_set_mouse_input(vlc_mediaPlayer, 0);
	libvlc_video_set_key_input(vlc_mediaPlayer, 0);
 
	// 获取各种元数据
	const char *title = libvlc_media_get_meta(vlc_media, libvlc_meta_Title);
	const char *artist = libvlc_media_get_meta(vlc_media, libvlc_meta_Artist);
	const char *album = libvlc_media_get_meta(vlc_media, libvlc_meta_Album);
	const char *url = libvlc_media_get_meta(vlc_media, libvlc_meta_URL);
	const char *date = libvlc_media_get_meta(vlc_media, libvlc_meta_Date);
	const char *lang = libvlc_media_get_meta(vlc_media, libvlc_meta_Language);
	int duration = libvlc_media_get_duration(vlc_media);  // 获取时长（单位：毫秒）
 
	qDebug("Title: %s", title ? title : "N/A");
	qDebug("Artist: %s", artist ? artist : "N/A");
	qDebug("Album: %s", album ? album : "N/A");
	qDebug("Duration: %d ms", duration);
	qDebug("url: %s", url ? url : "N/A");
	qDebug("date: %s", date ? date : "N/A");
	qDebug("lang: %s", lang ? lang : "N/A");
	
	libvlc_media_track_t **tracks;
	int track_count = libvlc_media_tracks_get(vlc_media,&tracks);
	for (unsigned i = 0; i < track_count; i++) 
	{
		libvlc_media_track_t* track = tracks[i];
 
		// 显示轨道信息
		printf("Track #%u: %s\n", i, track->psz_description);
 
		// 这里可以获取到每一个轨道的信息，比如轨道类型 track->i_type
		// 可能是 libvlc_track_video, libvlc_track_audio 或者 libvlc_track_text (字幕)
 
		if (track->i_type == libvlc_track_video) {
			// 处理视频轨道信息
			qDebug("width = %d",track->video->i_width);
			qDebug("height = %d", track->video->i_height);
			qDebug("rate_num = %d", track->video->i_frame_rate_num);
			qDebug("rate_den = %d", track->video->i_frame_rate_den);
		}
		else if (track->i_type == libvlc_track_audio) {
			// 处理音频轨道信息
			qDebug("channels = %d", track->audio->i_channels);
			qDebug("rate = %d", track->audio->i_rate);
		}
		else if (track->i_type == libvlc_track_text) {
			// 处理字幕轨道信息
		}
	}
 
	//获取事件管理器
	libvlc_event_manager_t *em = libvlc_media_player_event_manager(vlc_mediaPlayer);
 
	// 注册事件监听器
	libvlc_event_attach(em, libvlc_MediaPlayerTimeChanged, vlcEvents, this);
	libvlc_event_attach(em, libvlc_MediaPlayerEndReached, vlcEvents, this);
	libvlc_event_attach(em, libvlc_MediaPlayerStopped, vlcEvents, this);
	libvlc_event_attach(em, libvlc_MediaPlayerPlaying, vlcEvents, this);
	libvlc_event_attach(em, libvlc_MediaPlayerPaused, vlcEvents, this);
 
	libvlc_media_player_set_hwnd(vlc_mediaPlayer, (void *)ui.widgetShow->winId());
 
	QTimer::singleShot(1000, this, &showWidget::slotPlay);
 
}
 
void showWidget::slotPlay()
{
	if (vlc_mediaPlayer)
	{
		libvlc_media_player_play(vlc_mediaPlayer);
		m_defalutScale = libvlc_video_get_scale(vlc_mediaPlayer);
	}
	
}
 
void showWidget::slotPause()
{
	if (vlc_mediaPlayer)
		libvlc_media_player_pause(vlc_mediaPlayer);
}
 
void showWidget::slotStop()
{
	if (vlc_mediaPlayer)
		libvlc_media_player_stop(vlc_mediaPlayer);
}
 
void showWidget::slotValueChanged(int value)
{
	if (vlc_mediaPlayer)
		libvlc_audio_set_volume(vlc_mediaPlayer, value);
}
 
void showWidget::slotCurrentIndexChanged(int index)
{
	if (vlc_mediaPlayer)
		libvlc_media_player_set_rate(vlc_mediaPlayer, m_lstRate[index]);
}
 
void showWidget::slotActionTriggered(QAction *action)
{
	if (!vlc_mediaPlayer)
		return;
 
	if (action == m_default)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer,m_defalutRate);
	else if(action == m_16_9)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "16:9");
	else if (action == m_4_3)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "4:3");
	else if (action == m_1_1)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "1:1");
	else if (action == m_16_10)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "16:10");
	else if (action == m_2_21_1)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "221:100");
	else if (action == m_2_35_1)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "235:100");
	else if (action == m_2_38_1)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "238:100");
	else if (action == m_5_4)
		libvlc_video_set_aspect_ratio(vlc_mediaPlayer, "5:4");
 
	action->setIcon(QIcon(":/image/images/point.png"));
	m_preAspectRatio->setIcon(QIcon());
	m_preAspectRatio = action;
}
 
void showWidget::slotCropActionTriggered(QAction *action)
{
	if (!vlc_mediaPlayer)
		return;
 
	if (action == m__cropDefault)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, m_defalutCrop);
	else if (action == m__crop16_10)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "16:10");
	else if (action == m__crop16_9)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "16:9");
	else if (action == m__crop4_3)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "4:3");
	else if (action == m__crop1_85_1)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "185:100");
	else if (action == m__crop2_21_1)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "221:100");
	else if (action == m__crop2_35_1)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "235:100");
	else if (action == m__crop2_39_1)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "239:100");
	else if (action == m__crop5_3)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "5:3");
	else if (action == m__crop5_4)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "5:4");
	else if (action == m__crop1_1)
		libvlc_video_set_crop_geometry(vlc_mediaPlayer, "1:1");
 
	action->setIcon(QIcon(":/image/images/point.png"));
	m_preCrop->setIcon(QIcon());
	m_preCrop = action;
}
 
void showWidget::slotScaleActionTriggered(QAction *action)
{
	if (!vlc_mediaPlayer)
		return;
 
	if (action == m_scale1_4)
		libvlc_video_set_scale(vlc_mediaPlayer, 0.25);
	else if (action == m_scale1_2)
		libvlc_video_set_scale(vlc_mediaPlayer, 0.5);
	else if (action == m_scale1_1)
		libvlc_video_set_scale(vlc_mediaPlayer, 1);
	else if (action == m_scale2_1)
		libvlc_video_set_scale(vlc_mediaPlayer, 2);
 
	action->setIcon(QIcon(":/image/images/point.png"));
	m_preScale->setIcon(QIcon());
	m_preScale = action;
}
 
void showWidget::slotSnap()
{
	if (vlc_mediaPlayer)
	{
		QString path = "./snap.png";
		libvlc_video_take_snapshot(vlc_mediaPlayer, 0, path.toUtf8().data(), 0, 0);
	}
}
 
//事件回调
void showWidget::vlcEvents(const libvlc_event_t *ev, void *param)
{
	showWidget *w = (showWidget*)param;
	//处理不同的事件
	switch (ev->type) {
	case libvlc_MediaPlayerTimeChanged:
	{
		//qDebug() << "VLC媒体播放器时间已更改";
		qint64 len = libvlc_media_player_get_time(w->vlc_mediaPlayer);
		libvlc_time_t lenSec = len / 1000;
 
		libvlc_time_t totalLen = libvlc_media_player_get_length(w->vlc_mediaPlayer);
		libvlc_time_t totalLenSec = totalLen / 1000;
 
		int thh, tmm, tss;
		thh = lenSec / 3600;
		tmm = (lenSec % 3600) / 60;
		tss = (lenSec % 60);
		QTime time(thh, tmm, tss);
		w->ui.lbCurTime->setText(time.toString("hh:mm:ss"));
 
		thh = totalLenSec / 3600;
		tmm = (totalLenSec % 3600) / 60;
		tss = (totalLenSec % 60);
		QTime TotalTime(thh, tmm, tss);
		w->ui.lbTotalTime->setText(TotalTime.toString("hh:mm:ss"));
 
		double pos = (double)lenSec / totalLenSec * 100;
		w->ui.horizontalSlider->setValue(pos);
	}
		break;
	case libvlc_MediaPlayerEndReached:
		qDebug() << "VLC播放完毕.";
		break;
	case libvlc_MediaPlayerStopped:
		qDebug() << "VLC停止播放";
		break;
	case libvlc_MediaPlayerPlaying:
		qDebug() << "VLC开始播放";
		break;
	case libvlc_MediaPlayerPaused:
		qDebug() << "VLC暂停播放";
		break;
	}
}
 
void showWidget::initMenu()
{
	//总菜单
	m_menu = new QMenu(this);
	m_video = m_menu->addAction("视频");
 
	//视频菜单
	m_videoMenu = new QMenu(this);
	m_scaleAction = m_videoMenu->addAction("缩放");
	m_aspectRatioAction = m_videoMenu->addAction("宽高比");
	m_cropAction = m_videoMenu->addAction("裁剪");
	m_snapAction = m_videoMenu->addAction("截图");
	connect(m_snapAction, &QAction::triggered, this, &showWidget::slotSnap);
 
	m_video->setMenu(m_videoMenu);
 
	//宽高比菜单
	m_aspectRatioMenu = new QMenu(this);
	m_aspectRatioAction->setMenu(m_aspectRatioMenu);
 
	//设置宽高比菜单
	m_default = m_aspectRatioMenu->addAction(QIcon(":/image/images/point.png"), "默认");
	m_16_9 = m_aspectRatioMenu->addAction("16:9");
	m_4_3 = m_aspectRatioMenu->addAction("4:3");
	m_1_1 = m_aspectRatioMenu->addAction("1:1");
	m_16_10 = m_aspectRatioMenu->addAction("16:10");
	m_2_21_1 = m_aspectRatioMenu->addAction("2.21:1");
	m_2_35_1 = m_aspectRatioMenu->addAction("2.35:1");
	m_2_38_1 = m_aspectRatioMenu->addAction("2.38:1");
	m_5_4 = m_aspectRatioMenu->addAction("5:4");
 
	m_preAspectRatio = m_default;
 
	m_group = new QActionGroup(this);
	m_group->addAction(m_default);
	m_group->addAction(m_16_9);
	m_group->addAction(m_4_3);
	m_group->addAction(m_1_1);
	m_group->addAction(m_16_10);
	m_group->addAction(m_2_21_1);
	m_group->addAction(m_2_35_1);
	m_group->addAction(m_2_38_1);
	m_group->addAction(m_5_4);
 
	connect(m_group, &QActionGroup::triggered, this, &showWidget::slotActionTriggered);
 
	//设置裁剪菜单
	m_cropMenu = new QMenu(this);
	m_cropAction->setMenu(m_cropMenu);
 
	m__cropDefault = m_cropMenu->addAction(QIcon(":/image/images/point.png"), "默认");
	m__crop16_10 = m_cropMenu->addAction("16:10");
	m__crop16_9 = m_cropMenu->addAction("16:9");
	m__crop4_3 = m_cropMenu->addAction("4:3");
	m__crop1_85_1 = m_cropMenu->addAction("1.85:1");
	m__crop2_21_1 = m_cropMenu->addAction("2.21:1");
	m__crop2_35_1 = m_cropMenu->addAction("2.35:1");
	m__crop2_39_1 = m_cropMenu->addAction("2.39:1");
	m__crop5_3 = m_cropMenu->addAction("5:3");
	m__crop5_4 = m_cropMenu->addAction("5:4");
	m__crop1_1 = m_cropMenu->addAction("1:1");
 
	m_preCrop = m__cropDefault;
 
	m_cropGroup = new QActionGroup(this);
	m_cropGroup->addAction(m__cropDefault);
	m_cropGroup->addAction(m__crop16_10);
	m_cropGroup->addAction(m__crop16_9);
	m_cropGroup->addAction(m__crop4_3);
	m_cropGroup->addAction(m__crop1_85_1);
	m_cropGroup->addAction(m__crop2_21_1);
	m_cropGroup->addAction(m__crop2_35_1);
	m_cropGroup->addAction(m__crop2_39_1);
	m_cropGroup->addAction(m__crop5_3);
	m_cropGroup->addAction(m__crop5_4);
	m_cropGroup->addAction(m__crop1_1);
 
	connect(m_cropGroup, &QActionGroup::triggered, this, &showWidget::slotCropActionTriggered);
 
 
	//设置缩放菜单
	m_scaleMenu = new QMenu(this);
	m_scaleAction->setMenu(m_scaleMenu);
 
	m_scale1_4 = m_scaleMenu->addAction("1:4 四分之一");
	m_scale1_2 = m_scaleMenu->addAction("1:2 二分之一");
	m_scale1_1 = m_scaleMenu->addAction(QIcon(":/image/images/point.png"),"1:1 原始");
	m_scale2_1 = m_scaleMenu->addAction("2:1 双倍");
 
	m_scaleGroup = new QActionGroup(this);
	m_scaleGroup->addAction(m_scale1_4);
	m_scaleGroup->addAction(m_scale1_2);
	m_scaleGroup->addAction(m_scale1_1);
	m_scaleGroup->addAction(m_scale2_1);
 
	m_preScale = m_scale1_1;
 
	connect(m_scaleGroup, &QActionGroup::triggered, this, &showWidget::slotScaleActionTriggered);
}

更多参考：

libVLC 事件机制-CSDN博客

libVLC windows开发环境搭建-CSDN博客

https://sunnnnnn666.blog.csdn.net/article/details/137023036