ffmpeg 解码h264 qt显示

你可以使用`ffmpeg`库来解码H.264视频并在Qt应用程序中显示。下面是一个基本的示例代码：

#include <QApplication>
#include <QLabel>
#include <QTimer>
#include <QDebug>
#include <QByteArray>
extern "C" {
    #include <libavcodec/avcodec.h>
    #include <libavformat/avformat.h>
    #include <libswscale/swscale.h>
}

AVFormatContext *pFormatCtx = nullptr;
AVCodecContext *pCodecCtx = nullptr;
AVCodec *pCodec = nullptr;
AVFrame *pFrame = nullptr;
AVFrame *pFrameRGB = nullptr;
uint8_t *buffer = nullptr;
struct SwsContext *sws_ctx = nullptr;

bool openVideo(const char *filename)
{
    if (avformat_open_input(&pFormatCtx, filename, nullptr, nullptr) != 0)
    {
        qDebug() << "Could not open file";
        return false;
    }

    if (avformat_find_stream_info(pFormatCtx, nullptr) < 0)
    {
        qDebug() << "Could not find stream information";
        return false;
    }

    int videoStream = -1;
    for (unsigned int i = 0; i < pFormatCtx->nb_streams; i++)
    {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            videoStream = i;
            break;
        }
    }
    if (videoStream == -1)
    {
        qDebug() << "Could not find video stream";
        return false;
    }

    pCodecCtx = avcodec_alloc_context3(nullptr);
    if (avcodec_parameters_to_context(pCodecCtx, pFormatCtx->streams[videoStream]->codecpar) != 0)
    {
        qDebug() << "Could not initialize codec context";
        return false;
    }

    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == nullptr)
    {
        qDebug() << "Codec not found";
        return false;
    }

    if (avcodec_open2(pCodecCtx, pCodec, nullptr) < 0)
    {
        qDebug() << "Could not open codec";
        return false;
    }

    pFrame = av_frame_alloc();
    pFrameRGB = av_frame_alloc();

    int numBytes = av_image_get_buffer_size(AV_PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height, 1);
    buffer = new uint8_t[numBytes];
    av_image_fill_arrays(pFrameRGB->data, pFrameRGB->linesize, buffer, AV_PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height, 1);

    sws_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                             pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_RGB24,
                             SWS_BILINEAR, nullptr, nullptr, nullptr);
    
    return true;
}

void closeVideo()
{
    if (sws_ctx != nullptr)
        sws_freeContext(sws_ctx);
    if (pFrameRGB != nullptr)
        av_frame_free(&pFrameRGB);
    if (pFrame != nullptr)
        av_frame_free(&pFrame);
    if (pCodecCtx != nullptr)
        avcodec_free_context(&pCodecCtx);
    if (pFormatCtx != nullptr)
        avformat_close_input(&pFormatCtx);
    if (buffer != nullptr)
        delete[] buffer;
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel label;
    label.show();

    if (!openVideo("path/to/your/video.mp4"))
    {
        qDebug() << "Failed to open video";
        return -1;
    }

    QTimer timer;
    QObject::connect(&timer, &QTimer::timeout, [&]() {
        AVPacket packet;
        while (av_read_frame(pFormatCtx, &packet) >= 0)
        {
            if (packet.stream_index == pCodecCtx->video_stream_index)
            {
                avcodec_send_packet(pCodecCtx, &packet);
                while (avcodec_receive_frame(pCodecCtx, pFrame) == 0)
                {
                    sws_scale(sws_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);
                    QImage img(pFrameRGB->data[0], pCodecCtx->width, pCodecCtx->height, QImage::Format_RGB888);
                    label.setPixmap(QPixmap::fromImage(img));
                    label.adjustSize();
                }
            }
            av_packet_unref(&packet);
        }
    });
    timer.start(33);  // 30 FPS

    int result = a.exec();

    closeVideo();

    return result;
}

你需要将路径 `path/to/your/video.mp4` 替换为你的H.264视频文件路径。这个示例会在一个Qt窗口中显示视频帧。请注意，你需要通过Qt的一些方法来显示图像，例如使用`QLabel`来显示 `QImage`。