c++ - 在ffmpeg中使用复用读取编码数据

Question

我正在尝试使用 ffmpeg c++ 读取编码视频。当我尝试构建我的代码错误时出现标识符选项未定义。但它已经定义为 AVDictionary *options = NULL .

我的代码有什么问题？

void CFfmpegmethods::VideoRead(){

    const char *url = "H:/Sanduni_projects/ad_2.mp4";

    AVFormatContext *s = NULL;
    int ret = avformat_open_input(&s, url, NULL, NULL);
    if (ret < 0)
        abort();

    avformat_find_stream_info(s, &options);

    AVDictionary *options = NULL;

    av_dict_set(&options, "video_size", "640x480", 0);
    av_dict_set(&options, "pixel_format", "rgb24", 0);

    if (avformat_open_input(&s, url, NULL, &options) < 0){
        abort();
    }

    av_dict_free(&options);

    AVDictionaryEntry *e;

    if (e = av_dict_get(options, "", NULL, AV_DICT_IGNORE_SUFFIX)) {
        fprintf(stderr, "Option %s not recognized by the demuxer.\n", e->key);
        abort();
    }

    avformat_close_input(&s);
}

Answer 1

注释掉 about()带来了options 的声明if 范围内的变量，所以你的代码这样做:

if (ret < 0)
{
    //abort();

    AVDictionary *options = NULL;
}

最好在分支后始终打开一个新的 {} 以避免此类问题:

if (ret < 0)
{
    //abort(); // now commenting this line does not make scope to change
}
AVDictionary *options = NULL;