libVLC 视频抓图-编程知识

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 itemm = 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_OBJECTpublic: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menuvoid 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