ffmpeg 解封装解码实战

本代码主要讲解了如何打开流媒体封装格式flv、mp4，获取音视频的信息，打印了前十帧音视频信息作为分析对象。

源代码：

#include <stdio.h>
#include <libavformat/avformat.h>


int main(int argc, char **argv)
{
    //打开网络流。这里如果只需要读取本地媒体文件，不需要用到网络功能，可以不用加上这一句
//    avformat_network_init();

    const char *default_filename = "believe.mp4";

    char *in_filename = NULL;

    if(argv[1] == NULL)
    {
        in_filename = default_filename;
    }
    else
    {
        in_filename = argv[1];
    }
    printf("in_filename = %s\n", in_filename);

    //AVFormatContext是描述一个媒体文件或媒体流的构成和基本信息的结构体
    AVFormatContext *ifmt_ctx = NULL;           // 输入文件的demux

    int videoindex = -1;        // 视频索引
    int audioindex = -1;        // 音频索引


    // 打开文件，主要是探测协议类型，如果是网络文件则创建网络链接
    int ret = avformat_open_input(&ifmt_ctx, in_filename, NULL, NULL);
    if (ret < 0)  //如果打开媒体文件失败，打印失败原因
    {
        char buf[1024] = { 0 };
        av_strerror(ret, buf, sizeof(buf) - 1);
        printf("open %s failed:%s\n", in_filename, buf);
        goto failed;
    }

    ret = avformat_find_stream_info(ifmt_ctx, NULL);
    if (ret < 0)  //如果打开媒体文件失败，打印失败原因
    {
        char buf[1024] = { 0 };
        av_strerror(ret, buf, sizeof(buf) - 1);
        printf("avformat_find_stream_info %s failed:%s\n", in_filename, buf);
        goto failed;
    }

    //打开媒体文件成功
    printf_s("\n==== av_dump_format in_filename:%s ===\n", in_filename);
    av_dump_format(ifmt_ctx, 0, in_filename, 0);
    printf_s("\n==== av_dump_format finish =======\n\n");
    // url: 调用avformat_open_input读取到的媒体文件的路径/名字
    printf("media name:%s\n", ifmt_ctx->url);
    // nb_streams: nb_streams媒体流数量
    printf("stream number:%d\n", ifmt_ctx->nb_streams);
    // bit_rate: 媒体文件的码率,单位为bps
    printf("media average ratio:%lldkbps\n",(int64_t)(ifmt_ctx->bit_rate/1024));
    // 时间
    int total_seconds, hour, minute, second;
    // duration: 媒体文件时长，单位微妙
    total_seconds = (ifmt_ctx->duration) / AV_TIME_BASE;  // 1000us = 1ms, 1000ms = 1秒
    hour = total_seconds / 3600;
    minute = (total_seconds % 3600) / 60;
    second = (total_seconds % 60);
    //通过上述运算，可以得到媒体文件的总时长
    printf("total duration: %02d:%02d:%02d\n", hour, minute, second);
    printf("\n");
    /*
     * 老版本通过遍历的方式读取媒体文件视频和音频的信息
     * 新版本的FFmpeg新增加了函数av_find_best_stream，也可以取得同样的效果
     */
    for (uint32_t i = 0; i < ifmt_ctx->nb_streams; i++)
    {
        AVStream *in_stream = ifmt_ctx->streams[i];// 音频流、视频流、字幕流
        //如果是音频流，则打印音频的信息
        if (AVMEDIA_TYPE_AUDIO == in_stream->codecpar->codec_type)
        {
            printf("----- Audio info:\n");
            // index: 每个流成分在ffmpeg解复用分析后都有唯一的index作为标识
            printf("index:%d\n", in_stream->index);
            // sample_rate: 音频编解码器的采样率，单位为Hz
            printf("samplerate:%dHz\n", in_stream->codecpar->sample_rate);
            // codecpar->format: 音频采样格式
            if (AV_SAMPLE_FMT_FLTP == in_stream->codecpar->format)
            {
                printf("sampleformat:AV_SAMPLE_FMT_FLTP\n");
            }
            else if (AV_SAMPLE_FMT_S16P == in_stream->codecpar->format)
            {
                printf("sampleformat:AV_SAMPLE_FMT_S16P\n");
            }
            // channels: 音频信道数目
            printf("channel number:%d\n", in_stream->codecpar->channels);
            // codec_id: 音频压缩编码格式
            if (AV_CODEC_ID_AAC == in_stream->codecpar->codec_id)
            {
                printf("audio codec:AAC\n");
            }
            else if (AV_CODEC_ID_MP3 == in_stream->codecpar->codec_id)
            {
                printf("audio codec:MP3\n");
            }
            else
            {
                printf("audio codec_id:%d\n", in_stream->codecpar->codec_id);
            }
            // 音频总时长，单位为秒。注意如果把单位放大为毫秒或者微妙，音频总时长跟视频总时长不一定相等的
            if(in_stream->duration != AV_NOPTS_VALUE)
            {
                int duration_audio = (in_stream->duration) * av_q2d(in_stream->time_base);
                //将音频总时长转换为时分秒的格式打印到控制台上
                printf("audio duration: %02d:%02d:%02d\n",
                       duration_audio / 3600, (duration_audio % 3600) / 60, (duration_audio % 60));
            }
            else
            {
                printf("audio duration unknown");
            }

            printf("\n");

            audioindex = i; // 获取音频的索引
        }
        else if (AVMEDIA_TYPE_VIDEO == in_stream->codecpar->codec_type)  //如果是视频流，则打印视频的信息
        {
            printf("----- Video info:\n");
            printf("index:%d\n", in_stream->index);
            // avg_frame_rate: 视频帧率,单位为fps，表示每秒出现多少帧
            printf("fps:%lffps\n", av_q2d(in_stream->avg_frame_rate));
            if (AV_CODEC_ID_MPEG4 == in_stream->codecpar->codec_id) //视频压缩编码格式
            {
                printf("video codec:MPEG4\n");
            }
            else if (AV_CODEC_ID_H264 == in_stream->codecpar->codec_id) //视频压缩编码格式
            {
                printf("video codec:H264\n");
            }
            else
            {
                printf("video codec_id:%d\n", in_stream->codecpar->codec_id);
            }
            // 视频帧宽度和帧高度
            printf("width:%d height:%d\n", in_stream->codecpar->width,
                   in_stream->codecpar->height);
            //视频总时长，单位为秒。注意如果把单位放大为毫秒或者微妙，音频总时长跟视频总时长不一定相等的
            if(in_stream->duration != AV_NOPTS_VALUE)
            {
                int duration_video = (in_stream->duration) * av_q2d(in_stream->time_base);
                printf("video duration: %02d:%02d:%02d\n",
                       duration_video / 3600,
                       (duration_video % 3600) / 60,
                       (duration_video % 60)); //将视频总时长转换为时分秒的格式打印到控制台上
            }
            else
            {
                printf("video duration unknown");
            }

            printf("\n");
            videoindex = i;
        }
    }

    AVPacket *pkt = av_packet_alloc();

    int pkt_count = 0;
    int print_max_count = 10;
    printf("\n-----av_read_frame start\n");
    while (1)
    {
        ret = av_read_frame(ifmt_ctx, pkt);
        if (ret < 0)
        {
            printf("av_read_frame end\n");
            break;
        }

        if(pkt_count++ < print_max_count)
        {
            if (pkt->stream_index == audioindex)
            {
                printf("audio pts: %lld\n", pkt->pts);
                printf("audio dts: %lld\n", pkt->dts);
                printf("audio size: %d\n", pkt->size);
                printf("audio pos: %lld\n", pkt->pos);
                printf("audio duration: %lf\n\n",
                       pkt->duration * av_q2d(ifmt_ctx->streams[audioindex]->time_base));
            }
            else if (pkt->stream_index == videoindex)
            {
                printf("video pts: %lld\n", pkt->pts);
                printf("video dts: %lld\n", pkt->dts);
                printf("video size: %d\n", pkt->size);
                printf("video pos: %lld\n", pkt->pos);
                printf("video duration: %lf\n\n",
                       pkt->duration * av_q2d(ifmt_ctx->streams[videoindex]->time_base));
            }
            else
            {
                printf("unknown stream_index:\n", pkt->stream_index);
            }
        }

        av_packet_unref(pkt);
    }

    if(pkt)
        av_packet_free(&pkt);
failed:
    if(ifmt_ctx)
        avformat_close_input(&ifmt_ctx);


    getchar(); //加上这一句，防止程序打印完信息马上退出
    return 0;
}

输出结果：

in_filename = believe.flv

==== av_dump_format in_filename:believe.flv ===
Input #0, flv, from 'believe.flv':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    comment         : www.ieway.cn
    encoder         : Lavf58.29.100
  Duration: 00:03:42.53, start: 0.000000, bitrate: 286 kb/s
    Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 1920x1080, 150 kb/s, 14.46 fps, 15 tbr, 1k tbn, 30 tbc
    Stream #0:1: Audio: aac (LC), 48000 Hz, stereo, fltp, 128 kb/s

==== av_dump_format finish =======

media name:believe.flv
stream number:2
media average ratio:279kbps
total duration: 00:03:42

----- Video info:
index:0
fps:14.464286fps
video codec:H264
width:1920 height:1080
video duration unknown
----- Audio info:
index:1
samplerate:48000Hz
sampleformat:AV_SAMPLE_FMT_FLTP
channel number:2
audio codec:AAC
audio duration unknown

-----av_read_frame start
audio pts: 0
audio dts: 0
audio size: 341
audio pos: 502
audio duration: 0.021000

video pts: 14
video dts: 14
video size: 66736
video pos: 860
video duration: 0.066000

audio pts: 21
audio dts: 21
audio size: 341
audio pos: 67616
audio duration: 0.021000

audio pts: 43
audio dts: 43
audio size: 342
audio pos: 67974
audio duration: 0.021000

audio pts: 64
audio dts: 64
audio size: 341
audio pos: 68333
audio duration: 0.021000

video pts: 81
video dts: 81
video size: 580
video pos: 68691
video duration: 0.066000

audio pts: 85
audio dts: 85
audio size: 341
audio pos: 69291
audio duration: 0.021000

audio pts: 107
audio dts: 107
audio size: 342
audio pos: 69649
audio duration: 0.021000

audio pts: 128
audio dts: 128
audio size: 341
audio pos: 70008
audio duration: 0.021000

video pts: 147
video dts: 147
video size: 11289
video pos: 70366
video duration: 0.066000

av_read_frame end