一、通过此文可以得到什么

通过此练习：

1、知道了如何计算一个音频和视频的播放时间；2、知道了音视频解码的思路的大体流程，之后无非就是在这个流程上进行扩充细节；3、知道了如何通过C语言或者C++编程语言结合ffmpeg拿到一些音视频的关键信息，例如：帧率等；二、实现思路

关注+私信扣1，无偿分享2022最新最全学习提升资料包,资料内容包括《Andoird音视频开发必备手册+音视频最新学习视频+大厂面试真题+2022最新学习路线图+项目实战源码》（C/C++，Linux，FFmpeg ，webRTC ，rtmp ，hls ，rtsp ，ffplay ，srs）等等

三、实现效果

zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ makemake allmake[1]: 进入目录“/data/project/VSCProject/ffmpegStudy/src”Compiling main.cpp to main.o ..cp hello /data/project/VSCProject/ffmpegStudy/src/../# make 【hello】 finish !!!	make[1]: 离开目录“/data/project/VSCProject/ffmpegStudy/src”zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ ./hello Hello World !decode video fileName=/home/zhenghui/视频/1080P.mp4 [NULL @ 0x5654cc332d80] Opening '/home/zhenghui/视频/1080P.mp4' for reading[file @ 0x5654cc333380] Setting default whitelist 'file,crypto,data'[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Format mov,mp4,m4a,3gp,3g2,mj2 probed with size=2048 and score=100[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] ISO: File Type Major Brand: isom[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Unknown dref type 0x206c7275 size 12[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Processing st: 0, edit list 0 - media time: 1072, duration: 3621888[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Offset DTS by 1072 to make first pts zero.[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Setting codecpar->delay to 2 for stream st: 0[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Unknown dref type 0x206c7275 size 12[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Processing st: 1, edit list 0 - media time: 0, duration: 9990149[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 29.916667 0.006250[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 30.000000 0.000066[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 60.000000 0.000265[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 120.000000 0.001061[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 240.000000 0.004244[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 29.970030 0.000868[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 59.940060 0.003473[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Before avformat_find_stream_info() pos: 87425182 bytes read:315205 seeks:1 nb_streams:2[h264 @ 0x5654cc3340c0] nal_unit_type: 7(SPS), nal_ref_idc: 3[h264 @ 0x5654cc3340c0] nal_unit_type: 8(PPS), nal_ref_idc: 3[h264 @ 0x5654cc3340c0] nal_unit_type: 7(SPS), nal_ref_idc: 3[h264 @ 0x5654cc3340c0] nal_unit_type: 8(PPS), nal_ref_idc: 3[h264 @ 0x5654cc3340c0] nal_unit_type: 6(SEI), nal_ref_idc: 0[h264 @ 0x5654cc3340c0] nal_unit_type: 5(IDR), nal_ref_idc: 3[h264 @ 0x5654cc3340c0] Format yuv420p chosen by get_format().[h264 @ 0x5654cc3340c0] Reinit context to 1920x1088, pix_fmt: yuv420p[h264 @ 0x5654cc3340c0] no picture [mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] All info found[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] After avformat_find_stream_info() pos: 53231 bytes read:393067 seeks:2 frames:4video_index=0 audio_index=1 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/zhenghui/视频/1080P.mp4':  Metadata:    major_brand     : isom    minor_version   : 512    compatible_brands: isomiso2avc1mp41    encoder         : Lavf58.29.100    description     : Packed by Bilibili XCoder v2.0.2  Duration: 00:03:46.53, start: 0.000000, bitrate: 3087 kb/s  Stream #0:0[0x1](und), 3, 1/16000: Video: h264 (High), 1 reference frame (avc1 / 0x31637661), yuv420p(progressive, left), 1920x1080 (1920x1088) [SAR 1:1 DAR 16:9], 0/1, 2951 kb/s, 30 fps, 30 tbr, 16k tbn (default)    Metadata:      handler_name    : VideoHandler      vendor_id       : [0][0][0][0]  Stream #0:1[0x2](und), 1, 1/44100: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)    Metadata:      handler_name    : SoundHandler      vendor_id       : [0][0][0][0]media name =/home/zhenghui/视频/1080P.mp4 stream number: 2 media average ratio: 3015 kbpsmedia total time: 0:3:46 ######## Video info: ######## stream index : 0 fps:29.999914 fpsvideo codec : H264 video_time : 00:03:46######## Audio info: ######## stream index : 1 stream sample_rate : 44100 Hz stream format : AV_SAMPLE_FMT_FLTP channels number:2 audio codec:AAC audio_time : 00:03:46[AVIOContext @ 0x5654cc33b7c0] Statistics: 393067 bytes read, 2 seekszhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ 

#include <iostream>#include <stdio.h>#ifdef __cplusplus //表示是一个c++程序extern "C"{#endif#include <libavdevice/avdevice.h>#include <libavutil/frame.h>#include <libavutil/imgutils.h>#include <libavutil/log.h>#include <libswscale/swscale.h>#include <libavformat/avformat.h>#include <libavcodec/avcodec.h>#ifdef __cplusplus}#endif//g++ -I ../include/ hello_world.cpp -o hello_world -L../lib/ -lavcodec -lavdevice -lavfilter -lavformat -lavutilvoid decode(){    char *fileName = "/home/zhenghui/视频/1080P.mp4";     printf("decode video fileName=%s \n",fileName);    int ret = 0;    // 1、分配解复用器上下文    AVFormatContext *ctx = NULL;    ctx = avformat_alloc_context();     // 2、根据url打开本地文件或网络流    ret = avformat_open_input(&ctx,fileName,NULL,NULL);    if(ret < 0)    {        printf("打开%s失败 ! \n",fileName);        return;    }    // 3、读取媒体的部分数据包，获取码流信息    ret = avformat_find_stream_info(ctx,NULL);    if(ret < 0){        printf("获取码流信息失败 !\n");        return;    }    // 3、获取音频流和视频流的索引    int video_index = -1;    int audio_index = -1;    video_index = av_find_best_stream(ctx,AVMEDIA_TYPE_VIDEO,-1,-1,NULL,0);    printf("video_index=%d \n",video_index);    audio_index = av_find_best_stream(ctx,AVMEDIA_TYPE_AUDIO,-1,-1,NULL,0);    printf("audio_index=%d \n",audio_index);    // 打印流信息    av_dump_format(ctx,0,fileName,0);    //打印媒体文件url    printf("media name =%s \n",ctx->url);    //打印流数量    printf("stream number: %d \n",ctx->nb_streams);    //打印码率    printf("media average ratio: %lld kbps\n",(int64_t)(ctx->bit_rate/1024));    //打印时长    int total_seconds,hour,minute,second;    //ctx->duration的单位是微妙，先转换成秒，再进行转换成其他的时间单位就比较简单了    total_seconds = (ctx->duration) / AV_TIME_BASE;    hour = total_seconds / 3600;    minute = (total_seconds % 3600) /60;    second = (total_seconds % 60);    // 文件总时长    printf("media total time: %d:%d:%d \n",hour,minute,second);    //老版本查找流索引    for(int i = 0;i < ctx->nb_streams;i++){        AVStream  *av_stream = ctx->streams[i];        //判断流是什么类型        //视频流        if( AVMEDIA_TYPE_VIDEO == av_stream->codecpar->codec_type)        {            printf("######## Video info: ######## \n");            // 流索引            printf("stream index : %d \n",av_stream->index);            //帧率            printf("fps:%lf fps\n",av_q2d(av_stream->avg_frame_rate));            if(AV_CODEC_ID_MPEG4 == av_stream->codecpar->codec_id)            {                printf("video codec : MPEG4 \n");            }            else if(AV_CODEC_ID_H264 == av_stream->codecpar->codec_id)            {                printf("video codec : H264 \n");            }else             {                printf("video codec other value=%d \n", av_stream->codecpar->codec_id);            }            //获取视频总时长            if(AV_NOPTS_VALUE != av_stream->duration)            {                int video_time =av_stream->duration * av_q2d(av_stream->time_base);                printf("video_time : %02d:%02d:%02d\n" ,                (video_time / 3600),                (video_time % 3600) / 60,                (video_time % 60)                );            }            else{                printf("audio duration unknown ! \n");            }        }        //音频流        else if(AVMEDIA_TYPE_AUDIO == av_stream->codecpar->codec_type)        {            printf("######## Audio info: ######## \n");            // 流索引            printf("stream index : %d \n",av_stream->index);            // 音频编解码器的采样率 单位Hz            printf("stream sample_rate : %d Hz \n",av_stream->codecpar->sample_rate);            //音频采样格式            if(AV_SAMPLE_FMT_FLTP == av_stream->codecpar->format)            {                printf("stream format : AV_SAMPLE_FMT_FLTP \n");            }            else  if(AV_SAMPLE_FMT_S16P == av_stream->codecpar->format)            {                printf("stream format : AV_SAMPLE_FMT_S16P \n");            }else{                printf("stream format : other； value=%d \n",av_stream->codecpar->format);            }            // 音频信道数目            printf("channels number:%d \n",av_stream->codecpar->channels);            //音频压缩编码格式            if(AV_CODEC_ID_AAC == av_stream->codecpar->codec_id)            {                printf("audio codec:AAC \n");            }else if(AV_CODEC_ID_MP3 == av_stream->codecpar->codec_id)            {                printf("audio codec:MP3 \n");            }else{                printf("audio codec : other； value=%d \n",av_stream->codecpar->codec_id);            }            //获取视频总时长            if(AV_NOPTS_VALUE != av_stream->duration)            {                int audio_time =av_stream->duration * av_q2d(av_stream->time_base);                printf("audio_time : %02d:%02d:%02d\n" ,                (audio_time / 3600),                (audio_time % 3600) / 60,                (audio_time % 60)                );            }            else{                printf("audio duration unknown ! \n");            }            audio_index = i;        }    }    if(ctx)        avformat_close_input(&ctx);}int main() {    // 设置控制台输出级别    av_log_set_level(AV_LOG_DEBUG);    // // 打印输出字符串Hello World ！    av_log(NULL, AV_LOG_DEBUG, "%s", "Hello World !\n");    decode();    return 0;}