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。

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。

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。

cpp 复制代码

vlc_base = libvlc_new(0, NULL);

2.创建一个媒体播放器。

cpp 复制代码

    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。

cpp 复制代码

    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。

cpp 复制代码

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：

cpp 复制代码

	virtual QRectF boundingRect() const;

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

类定义如下：

cpp 复制代码

#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。

cpp 复制代码

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。

cpp 复制代码

#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_OBJECT

public:
    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