Qt音视频开发之利用ffmpeg实现解码本地摄像头

void CameraThreadFFmpeg::initCamera()
{
    //https://blog.csdn.net/weixin_37921201/article/details/120357826
    //命令行打开 ffplay -f dshow -i video="USB Video Device" -s 1280x720 -framerate 30

    //启动计时
    timer.restart();

    //参数字典
    AVDictionary *options = NULL;

    //设置分辨率
    QString size = QString("%1x%2").arg(videoWidth).arg(videoHeight);
    av_dict_set(&options, "video_size", size.toUtf8().constData(), 0);
    //设置帧率
    if (frameRate > 0) {
        av_dict_set(&options, "framerate", QString::number(frameRate).toUtf8().constData(), 0);
    }

    //设置输入格式(前提是要对应设备对应平台支持)
    //av_dict_set(&options, "input_format", "mjpeg", 0);

    //设置图像格式(有些设备设置了格式后帧率上不去)
    //av_dict_set(&options, "pixel_format", "yuyv422", 0);

    //打印设备列表
    //FFmpegHelper::showDevice();
    //打印设备参数
    //FFmpegHelper::showOption(cameraName);

    //实例化格式处理上下文
    formatCtx = avformat_alloc_context();

    AVInputFormatx *ifmt = NULL;
    QByteArray url = cameraName.toUtf8();
#if defined(Q_OS_WIN)
    //ifmt = av_find_input_format("vfwcap");
    ifmt = av_find_input_format("dshow");
    url = QString("video=%1").arg(cameraName).toUtf8();
#elif defined(Q_OS_LINUX)
    //ifmt = av_find_input_format("v4l2");
    ifmt = av_find_input_format("video4linux2");
#elif defined(Q_OS_MAC)
    ifmt = av_find_input_format("avfoundation");
#endif

    int result = avformat_open_input(&formatCtx, url.data(), ifmt, &options);
    av_dict_free(&options);
    if (result < 0) {
        debug("打开地址", "错误: 打开出错 " + FFmpegHelper::getError(result));
        return;
    }

    //获取流信息
    result = avformat_find_stream_info(formatCtx, NULL);
    if (result < 0) {
        debug("打开地址", "错误: 找流失败 " + FFmpegHelper::getError(result));
        return;
    }

    //获取最佳流索引
    AVCodecx *videoCodec;
    videoIndex = av_find_best_stream(formatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
    if (videoIndex < 0) {
        debug("打开地址", "错误: 未找到视频流");
        return;
    }

    //获取视频流
    AVStream *videoStream = formatCtx->streams[videoIndex];

    //查找视频解码器(如果上面av_find_best_stream第五个参数传了则这里不需要)
    AVCodecID codecID = FFmpegHelper::getCodecID(videoStream);
    videoCodec = avcodec_find_decoder(codecID);
    //videoCodec = avcodec_find_decoder_by_name("h264");
    if (!videoCodec) {
        debug("打开地址", "错误: 查找视频解码器失败");
        return;
    }

    //创建视频流解码器上下文
    videoCodecCtx = avcodec_alloc_context3(videoCodec);
    if (!videoCodecCtx) {
        debug("打开地址", "错误: 创建视频解码器上下文失败");
        return;
    }

    result = FFmpegHelper::copyContext(videoCodecCtx, videoStream, false);
    if (result < 0) {
        debug("打开地址", "错误: 设置视频解码器参数失败");
        return;
    }

    //设置解码器参数
    videoCodecCtx->flags |= AV_CODEC_FLAG_LOW_DELAY;
    videoCodecCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    videoCodecCtx->flags2 |= AV_CODEC_FLAG2_FAST;

    //打开视频解码器
    result = avcodec_open2(videoCodecCtx, videoCodec, NULL);
    if (result < 0) {
        debug("打开地址", "错误: 打开视频解码器失败 " + FFmpegHelper::getError(result));
        return;
    }

    //获取实际分辨率大小
    FFmpegHelper::getResolution(videoStream, videoWidth, videoHeight);
    //如果没有获取到宽高则返回
    if (videoWidth <= 0 || videoHeight <= 0) {
        debug("打开地址", "错误: 获取宽度高度失败");
        return;
    }

    //获取最终真实的帧率
    frameRate = av_q2d(videoStream->r_frame_rate);
    QString msg = QString("索引: %1 解码: %2 帧率: %3 宽高: %4x%5").arg(videoIndex).arg(videoCodec->name).arg(frameRate).arg(videoWidth).arg(videoHeight);
    debug("视频信息", msg);
    openCamera();
}

bool CameraThreadFFmpeg::openCamera()
{
    //分配内存
    packet = FFmpegHelper::creatPacket(NULL);
    videoFrame = av_frame_alloc();
    yuvFrame = av_frame_alloc();
    imageFrame = av_frame_alloc();

    //设置属性以便该帧对象正常
    yuvFrame->format = AV_PIX_FMT_YUV420P;
    yuvFrame->width = videoWidth;
    yuvFrame->height = videoHeight;

    //定义及获取像素格式
    AVPixelFormat srcFormat = AV_PIX_FMT_YUYV422;
    //通过解码器获取解码格式
    srcFormat = videoCodecCtx->pix_fmt;
    //各种转换速度比对 https://www.cnblogs.com/xumaojun/p/8541634.html
    int flags = SWS_FAST_BILINEAR;

    //分配视频帧数据(转yuv420)
    int yuvSize = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, videoWidth, videoHeight, 1);
    yuvData = (quint8 *)av_malloc(yuvSize * sizeof(quint8));
    av_image_fill_arrays(yuvFrame->data, yuvFrame->linesize, yuvData, AV_PIX_FMT_YUV420P, videoWidth, videoHeight, 1);
    //视频图像转换(转yuv420)
    yuvSwsCtx = sws_getContext(videoWidth, videoHeight, srcFormat, videoWidth, videoHeight, AV_PIX_FMT_YUV420P, flags, NULL, NULL, NULL);

    //分配视频帧数据(转rgb)
    int imageSize = av_image_get_buffer_size(AV_PIX_FMT_RGB24, videoWidth, videoHeight, 1);
    imageData = (quint8 *)av_malloc(imageSize * sizeof(quint8));
    av_image_fill_arrays(imageFrame->data, imageFrame->linesize, imageData, AV_PIX_FMT_RGB24, videoWidth, videoHeight, 1);
    //视频图像转换(转rgb)
    imageSwsCtx = sws_getContext(videoWidth, videoHeight, AV_PIX_FMT_YUV420P, videoWidth, videoHeight, AV_PIX_FMT_RGB24, flags, NULL, NULL, NULL);

    //打印媒体信息
    //av_dump_format(formatCtx, 0, 0, 0);
    QString msg = QString("源头: %1 目标: %2").arg(srcFormat).arg(videoMode == VideoMode_Painter ? AV_PIX_FMT_RGB24 : AV_PIX_FMT_YUV420P);
    debug("格式信息", msg);

    //初始化音频播放
    this->initAudioPlayer();
    //初始化滤镜
    this->initFilter();

    int time = timer.elapsed();
    debug("打开成功", QString("用时: %1 毫秒").arg(time));
    emit receivePlayStart(time);
    emit recorderStateChanged(RecorderState_Stopped, fileName);
    isOk = true;
    return isOk;
}