用ffmpeg解析mp4文件得到时长、比特率、音视频信息

以下是使用C++语言调用FFmpeg获取视频流和音频流信息的示例代码：

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>

extern "C" {
    #include <libavformat/avformat.h>
}

class MediaInfo {
public:
    std::string filename;
    double duration;
    int bitrate;
    std::vector<std::pair<int, int>> video_streams; // (width, height)
    std::vector<std::pair<int, int>> audio_streams; // (sample_rate, channels)

    MediaInfo(const std::string& filename_) : filename(filename_) {}
};

MediaInfo get_media_info(const std::string& filename) {
    int ret=0;
    MediaInfo info(filename);

    av_register_all();

    AVFormatContext* format_ctx = nullptr;
    ret=avformat_open_input(&format_ctx, filename.c_str(), nullptr, nullptr);
    if(ret < 0)
    {
        std::cout << "avformat_open_input error\n";
        return info;
    }
    avformat_find_stream_info(format_ctx, nullptr);

    info.duration = static_cast<double>(format_ctx->duration) / AV_TIME_BASE;
    info.bitrate = format_ctx->bit_rate;

    for (unsigned int i = 0; i < format_ctx->nb_streams; i++) {
        if (format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            int width = format_ctx->streams[i]->codecpar->width;
            int height = format_ctx->streams[i]->codecpar->height;
            info.video_streams.push_back({width, height});
        }
        else if (format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            int sample_rate = format_ctx->streams[i]->codecpar->sample_rate;
            int channels = format_ctx->streams[i]->codecpar->channels;
            info.audio_streams.push_back({sample_rate, channels});
        }
    }

    avformat_close_input(&format_ctx);

    return info;
}

// 测试
int main() {
    MediaInfo info = get_media_info("./example.mp4");

    std::cout << "文件名：" << info.filename << std::endl;
    std::cout << "时长：" << info.duration << "秒" << std::endl;
    std::cout << "比特率：" << info.bitrate << "bps" << std::endl;

    std::cout << "视频流信息：" << std::endl;
    for (unsigned int i = 0; i < info.video_streams.size(); i++) {
        std::cout << "  分辨率：" << info.video_streams[i].first << "x" << info.video_streams[i].second << std::endl;
    }

    std::cout << "音频流信息：" << std::endl;
    for (unsigned int i = 0; i < info.audio_streams.size(); i++) {
        std::cout << "  采样率：" << info.audio_streams[i].first << "Hz"
                  << ", 声道数：" << info.audio_streams[i].second << std::endl;
    }

    return 0;
}

上述代码通过AVFormatContext结构体和FFmpeg库函数avformat_open_input、avformat_find_stream_info等，获取MP4文件的视频流和音频流信息，并将结果存储到MediaInfo类中。在实际应用中，可以将上述代码封装成一个函数，方便地在程序中调用，达到自动化处理多个视频文件的目的。

编译运行：

book@ubuntu:~/Desktop/c++_study$ g++ -g -o test_ff test_ff.cpp -lavformat 
book@ubuntu:~/Desktop/c++_study$ ./test_ff 
文件名：./example.mp4
时长：5.888秒
比特率：434519bps
视频流信息：
  分辨率：720x480
音频流信息：
  采样率：16000Hz, 声道数：1