qt 利用ffmpeg播放视频

要在Qt中使用FFmpeg播放视频，您需要使用FFmpeg库来解码视频文件并将其渲染到Qt的QVideoFrame对象中。下面是一些基本步骤：

1. 在Qt项目中添加FFmpeg库的头文件和链接库。

2. 创建一个类来处理视频的解码和渲染。您可以使用FFmpeg库中的AVFormatContext和AVCodecContext来打开视频文件并获取视频流的基本信息。

3. 通过调用avcodec_send_packet()和avcodec_receive_frame()函数，将解码后的视频帧存储到一个QVideoFrame对象中。

4. 使用Qt的QMediaPlayer类来渲染QVideoFrame对象，以便在Qt应用程序中显示视频。

下面是一个简单的示例代码片段，它演示了如何使用Qt和FFmpeg来播放视频：

#include <QApplication>
#include <QMainWindow>
#include <QMediaPlayer>
#include <QVideoWidget>
#include <QFileDialog>
#include <QMessageBox>
#include <QtAV>
#include <QVideoFrame>

extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
}

class VideoPlayer : public QMainWindow
{
    Q_OBJECT

public:
    VideoPlayer(QWidget *parent = 0);
    ~VideoPlayer();

private slots:
    void openFile();
    void play();
    void pause();
    void stop();
    void videoFrameReady(QVideoFrame frame);

private:
    QPushButton *m_openButton;
    QPushButton *m_playButton;
    QPushButton *m_pauseButton;
    QPushButton *m_stopButton;
    QVideoWidget *m_videoWidget;
    QMediaPlayer *m_mediaPlayer;
    AVCodecContext *m_codecContext;
    AVFormatContext *m_formatContext;
    SwsContext *m_swsContext;
};

VideoPlayer::VideoPlayer(QWidget *parent)
    : QMainWindow(parent)
{
    m_openButton = new QPushButton(tr("Open"), this);
    connect(m_openButton, &QPushButton::clicked, this, &VideoPlayer::openFile);

    m_playButton = new QPushButton(tr("Play"), this);
    connect(m_playButton, &QPushButton::clicked, this, &VideoPlayer::play);

    m_pauseButton = new QPushButton(tr("Pause"), this);
    connect(m_pauseButton, &QPushButton::clicked, this, &VideoPlayer::pause);

    m_stopButton = new QPushButton(tr("Stop"), this);
    connect(m_stopButton, &QPushButton::clicked, this, &VideoPlayer::stop);

    m_videoWidget = new QVideoWidget(this);

    m_mediaPlayer = new QMediaPlayer(this, QMediaPlayer::VideoSurface);
    m_mediaPlayer->setVideoOutput(m_videoWidget);

    QVBoxLayout *layout = new QVBoxLayout(this);
    layout->addWidget(m_videoWidget);
    layout->addWidget(m_openButton);
    layout->addWidget(m_playButton);
    layout->addWidget(m_pauseButton);
    layout->addWidget(m_stopButton);

    QWidget *centralWidget = new QWidget(this);
    centralWidget->setLayout(layout);
    setCentralWidget(centralWidget);
}

VideoPlayer::~VideoPlayer()
{
    avcodec_close(m_codecContext);
    avformat_close_input(&m_formatContext);
    sws_freeContext(m_swsContext);
}

void VideoPlayer::openFile()
{
    QString fileName = QFileDialog::getOpenFileName(this, tr("Open File"), "", tr("Video Files (*.avi *.mp4 *.mkv)"));

    if (fileName.isEmpty())
    {
        return;
    }

    m_formatContext = avformat_alloc_context();

    if (avformat_open_input(&m_formatContext, fileName.toUtf8().data(), NULL, NULL) != 0)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not open file."));
        return;
    }

    if (avformat_find_stream_info(m_formatContext, NULL) < 0)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not find stream info."));
        return;
    }

    int videoStreamIndex = -1;
    AVCodecParameters *codecParameters = NULL;

    for (int i = 0; i < m_formatContext->nb_streams; i++)
    {
        codecParameters = m_formatContext->streams[i]->codecpar;

        if (codecParameters->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            videoStreamIndex = i;
            break;
        }
    }

    if (videoStreamIndex == -1)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not find video stream."));
        return;
    }

    AVCodec *codec = avcodec_find_decoder(codecParameters->codec_id);

    if (codec == NULL)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not find codec."));
        return;
    }

    m_codecContext = avcodec_alloc_context3(codec);

    if (avcodec_parameters_to_context(m_codecContext, codecParameters) != 0)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not copy codec context."));
        return;
    }

    if (avcodec_open2(m_codecContext, codec, NULL) < 0)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not open codec."));
        return;
    }

    m_swsContext = sws_getContext(m_codecContext->width, m_codecContext->height, m_codecContext->pix_fmt, m_codecContext->width, m_codecContext->height, AV_PIX_FMT_RGB32, SWS_BILINEAR, NULL, NULL, NULL);

    if (m_swsContext == NULL)
    {
        QMessageBox::warning(this, tr("Error"), tr("Could not create SwsContext."));
        return;
    }

    AVPacket packet;
    av_init_packet(&packet);

    while (av_read_frame(m_formatContext, &packet) >= 0)
    {
        if (packet.stream_index == videoStreamIndex)
        {
            AVFrame *frame = av_frame_alloc();

            int response = avcodec_send_packet(m_codecContext, &packet);

            if (response < 0)
            {
                QMessageBox::warning(this, tr("Error"), tr("Could not send packet."));
                return;
            }

            response = avcodec_receive_frame(m_codecContext, frame);

            if (response == AVERROR(EAGAIN) || response == AVERROR_EOF)
            {
                continue;
            }
            else if (response < 0)
            {
                QMessageBox::warning(this, tr("Error"), tr("Could not receive frame."));
                return;
            }

            QImage image(m_codecContext->width, m_codecContext->height, QImage::Format_RGBA8888);

            uint8_t *dest[4] = { image.bits(), NULL, NULL, NULL };
            int destLinesize[4] = { image.bytesPerLine(), 0, 0, 0 };

            sws_scale(m_swsContext, frame->data, frame->linesize, 0, frame->height, dest, destLinesize);

            QVideoFrame qFrame(image);
            videoFrameReady(qFrame);

            av_frame_unref(frame);
            av_packet_unref(&packet);
        }
    }
}

void VideoPlayer::play()
{
    m_mediaPlayer->play();
}

void VideoPlayer::pause()
{
    m_mediaPlayer->pause();
}

void VideoPlayer::stop()
{
    m_mediaPlayer->stop();
}

void VideoPlayer::videoFrameReady(QVideoFrame frame)
{
    m_mediaPlayer->stop();
    m_mediaPlayer->setVideoOutput(m_videoWidget);
    m_mediaPlayer->setMedia(QMediaContent(), &frame);
    m_mediaPlayer->play();
}

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    VideoPlayer player;
    player.show();
    return app.exec();
}

在这个例子中，我们使用了Qt的QMediaPlayer类来播放视频帧，使用FFmpeg库中的AVFormatContext和AVCodecContext来解码视频文件并使用SwsContext来将解码后的视频帧渲染到QVideoFrame对象中。