libVLC 提取视频帧使用QGraphicsView渲染

在前面章节中，我们讲解了如何使用QWidget渲染每一帧视频数据，这种方法对 CPU 负荷较高。

libVLC 提取视频帧使用QWidget渲染-CSDN博客

后面又讲解了使用OpenGL渲染每一帧视频数据，使用 OpenGL去绘制，利用 GPU 减轻 CPU 计算负荷。

libVLC 提取视频帧使用OpenGL渲染-CSDN博客

本章节介绍另一种方法来渲染视频，使用QGraphicsView来渲染。

以下是操作流程：

1.初始化 libVLC 实例。

vlc_base = libvlc_new(0, NULL);

2.创建一个媒体播放器。

    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;}

3.设置视频回调。

    libvlc_video_set_format_callbacks(vlc_mediaPlayer, setup, NULL);// 设置自定义视频输出libvlc_video_set_callbacks(vlc_mediaPlayer, lock, unlock, display, NULL);

4.创建QGraphicsScene场景对象，并设置矩形区域，QGraphicsView设置场景对象，然后在场景中添加一个QGraphicsItem对象，用于显示视频。


void showWidget::showEvent(QShowEvent *event)
{if (m_init)return;m_init = true;QRect rect = this->rect();rect -= QMargins(15, 15, 15, 91);m_scene = new QGraphicsScene(rect, this);ui.graphicsView->setScene(m_scene);m_item = new ShowGraphicsItem();m_item->setRect(rect);m_scene->addItem(m_item);
}

ShowGraphicsItem是继承QGraphicsItem类，需要重写以下两个方法：

	virtual QRectF boundingRect() const;virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = Q_NULLPTR);

类定义如下：

#pragma once
#include <QGraphicsItem>
#include <QPainter>
#include <QImage>class ShowGraphicsItem : public QGraphicsItem
{
public:ShowGraphicsItem(QGraphicsItem *parent = Q_NULLPTR);~ShowGraphicsItem();public:void setRect(const QRectF &rect);void setImage(const QImage &image);public:virtual QRectF boundingRect() const;virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = Q_NULLPTR);private:QImage m_image;QRectF m_rect;
};#include "ShowGraphicsItem.h"ShowGraphicsItem::ShowGraphicsItem(QGraphicsItem *parent /*= Q_NULLPTR*/): QGraphicsItem(parent)
{}ShowGraphicsItem::~ShowGraphicsItem()
{}void ShowGraphicsItem::setRect(const QRectF &rect)
{prepareGeometryChange();m_rect = rect;update();
}void ShowGraphicsItem::setImage(const QImage &image)
{m_image = image;update();
}QRectF ShowGraphicsItem::boundingRect() const
{return m_rect;
}void ShowGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget /*= Q_NULLPTR*/)
{painter->setRenderHint(QPainter::Antialiasing, true);painter->setRenderHint(QPainter::SmoothPixmapTransform, true);painter->setRenderHint(QPainter::TextAntialiasing, true);// 反走样painter->setRenderHint(QPainter::Antialiasing, true);painter->drawImage(this->boundingRect(), m_image);
}

5.提取视频帧数据，创建QImage对象，传入给ShowGraphicsItem显示。

static void unlock(void *opaque, void *picture, void *const *planes) {// 这里可以释放视频帧的锁char *buffer = (char *)*planes; //planes即为帧数据QImage image((unsigned char*)buffer, g_frame->width, g_frame->height, QImage::Format_ARGB32);m_this->updatePic(image);g_frame->mutex.unlock();
}void showWidget::updatePic(const QImage &image)
{m_item->setImage(image);
}

这里介绍回调函数的意义，请看以下链接。

libVLC 提取视频帧-CSDN博客

以下是ui界面设计：

运行结果：

代码示例：

这里使用声明了static showWidget* m_this = nullptr。
在构造函数中使用m_this = this赋值。
在unlock回调中构造好QImage对象，使用m_this->updatePic(image)更新界面。
重写了void resizeEvent(QResizeEvent *event);事件，使item跟随窗口大小变化而变化。

#pragma once#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>
#include <QGraphicsScene>
#include "ShowGraphicsItem.h"enum Rate
{Rate2X,Rate1_5X,Rate1_25X,Rate1_0X,Rate0_75X,Rate0_5X
};class showWidget : public QWidget
{Q_OBJECTpublic:showWidget(QWidget *parent = nullptr);~showWidget();public:void updatePic(const QImage &image);protected:void showEvent(QShowEvent *event);void resizeEvent(QResizeEvent *event);private slots:void slotOpenFile();void slotPlay();void slotPause();void slotStop();void slotValueChanged(int value);void slotCurrentIndexChanged(int index);private://事件处理回调static void vlcEvents(const libvlc_event_t *ev, void *param);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;QList<QString> m_lstAudioDevice;QGraphicsScene *m_scene = nullptr;ShowGraphicsItem *m_item = nullptr;bool m_init = false;
};#include "showWidget.h"
#include <QTimer>
#include <QTime>
#include <QMutex>
#include <stdlib.h> #pragma execution_character_set("utf-8")static showWidget* m_this = nullptr;struct Frame 
{int     width;int     height;uchar * pixels;QMutex mutex;
};static Frame *g_frame = nullptr;// 自定义视频输出模块的回调函数
static void *lock(void *opaque, void **planes) {g_frame->mutex.lock();*planes = g_frame->pixels;return 0;
}static void unlock(void *opaque, void *picture, void *const *planes) {// 这里可以释放视频帧的锁char *buffer = (char *)*planes; //planes即为帧数据QImage image((unsigned char*)buffer, g_frame->width, g_frame->height, QImage::Format_ARGB32);m_this->updatePic(image);g_frame->mutex.unlock();
}static void display(void *opaque, void *picture) {// 这里可以进行视频帧的显示或其他处理(void)opaque;
}static unsigned setup(void **opaque, char *chroma,unsigned *width, unsigned *height,unsigned *pitches,unsigned *lines)
{qDebug() << "chroma:" << QString(chroma) << "width:" << *width << ", height:" << *height;/* 开辟存放图像数据的内存块 */if (g_frame){if (g_frame->pixels){delete[] g_frame->pixels;g_frame->pixels = NULL;}delete g_frame;g_frame = NULL;}int w = *width;int h = *height;g_frame = new Frame;g_frame->pixels = new uchar[w * h * 4]; // 申请大小也为4通道的像素memset(g_frame->pixels, 0, w * h * 4);memcpy(chroma, "RV32", 4);g_frame->width = w;g_frame->height = h;*pitches = w * 4;*lines = h;return 1;
}showWidget::showWidget(QWidget *parent): QWidget(parent)
{ui.setupUi(this);m_this = this;this->setWindowTitle("视频播放器");vlc_base = libvlc_new(0, NULL);ui.cbxRate->setCurrentIndex(Rate1_0X);m_lstRate << 2.0 << 1.5 << 1.25 << 1.0 << 0.75 << 0.5;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.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::updatePic(const QImage &image)
{m_item->setImage(image);
}void showWidget::showEvent(QShowEvent *event)
{if (m_init)return;m_init = true;QRect rect = this->rect();rect -= QMargins(15, 15, 15, 91);m_scene = new QGraphicsScene(rect, this);ui.graphicsView->setScene(m_scene);m_item = new ShowGraphicsItem();m_item->setRect(rect);m_scene->addItem(m_item);
}void showWidget::resizeEvent(QResizeEvent *event)
{if (!m_init)return;QRect rect = this->rect();rect -= QMargins(15, 15, 15, 91);m_scene->setSceneRect(rect);m_item->setRect(rect);
}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_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;}libvlc_video_set_format_callbacks(vlc_mediaPlayer, setup, NULL);// 设置自定义视频输出libvlc_video_set_callbacks(vlc_mediaPlayer, lock, unlock, display, NULL);// 等待元数据加载完成libvlc_media_parse(vlc_media);// 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);QTimer::singleShot(1000, this, &showWidget::slotPlay);libvlc_video_filter_list_get(vlc_base);
}void showWidget::slotPlay()
{if (vlc_mediaPlayer){libvlc_media_player_play(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]);
}//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;}
}

更多参考：

libVLC 添加图片和文本水印-CSDN博客

libVLC 音频输出设备切换-CSDN博客

libVLC 音频立体声模式切换-CSDN博客

QT Graphics View_qtgraphicsview-CSDN博客

Qt+FFmpeg+opengl从零制作视频播放器-7.OpenGL播放视频_qt opengl视频播放器-CSDN博客

Qt+FFmpeg+opengl从零制作视频播放器-1.项目介绍_qt opengl视频播放器-CSDN博客