libavcodec 提供了一系列编码器的实现
libavformat 实现流协议，容器格式及其本IO访问
libavutil 包含了hash器，解码器和各种工具函数
libavfilter 提供各种音视频过虑器
libavdevice 提供了访问捕获设备和回放设备的接口
libswresample 实现了混音和重采样
libswscale 实现了色彩转换和缩放功能

1.FFmpeg 开发入门Log系统

av_log_set_level(AV_LOG_DEBUG)
av_log(NULL,AV_LOG_INFO,"%s/n",option)
阀值 以上的日志都会打印出来（比如比debug高的error等信息）；

程序内容：

#include<stdio.h>
#include<libavutil/log.h>
int main(int argc,char *argv[]){
    av_log_set_level(AV_LOG_DEBUG);
    av_log(NULL,AV_LOG_INFO,"hello world\n");
    return 0;
}

使用命令编译：clang -g -o ffmpeg_log f -lavutil
运行程序：./ffmpeg_log

2.FFmpeg 文件的删除与重命名

avpriv_io_delete()
avpriv_io_move()
程序内容：

#include<libavformat/avformat.h>
int main(int argc, char *argv[]){

  int ret = avpriv_io_delete("./myfile.txt");
  if(ret < 0){
      av_log(NULL,AV_LOG_ERROR,"fail to delete file");
      //如果ret小于0，则是出错的情况
      return -1;
  }
  return 0;
}

使用命令编译：clang -g -o ffmpeg_file ffmpeg_file.c pkg-config --libs libavformat
运行程序：./ffmpeg_file
提示：brew安装 brew install pkg-config

3.FFmpeg操作目录以及list 的实现

avio_open_dir()
avio_read_dir()
avio_close_dir()
AVIODirContext //操作目录的上下文
AVIODirEntry //目录项、用于存放文件名、文件大小信息

程序内容：

#include<libavutil/log.h>
#include<libavformat/avformat.h>

int main (int argc ,char *argv[]){
    int ret;
    AVIODirContext *ctx = NULL;
    AVIODirEntry *entry = NULL;
    av_log_set_level(AV_LOG_INFO);
    ret = avio_open_dir(&ctx,"./",NULL);
    if(ret<0){
        av_log(NULL,AV_LOG_ERROR,"cant open dir%s\n",av_err2str(ret));
        return -1;
    }
    while(1){
        ret = avio_read_dir(ctx,&entry);
        if(ret<0){
            av_log(NULL,AV_LOG_ERROR,"cant read dir :%s",av_err2str(ret));
            goto __fail;
        }
        if(!entry){
            break;
        }
        av_log(NULL,AV_LOG_INFO,"%12"PRId64"  %s \n",entry->size,entry->name);
        avio_free_directory_entry(&entry);
    }
    __fail:
    avio_close_dir(&ctx);

    return 0 ;
}

使用命令编译： clang -g -o ffmpeg_list ffmpeg_list.c pkg-config --libs libavformat libavutil
运行程序：./ffmpeg_list

4.FFmpeg处理流数据
AVFormatContext //格式上下文
AVStream //流
AVPacket //包
av_register_all() //将FFpmeg中的编解码库协议注册到程序中
avformat_open_input() //获取文件的上下文 AVFormatContext
avformat_close_input() //关闭文件的上下文
av_dump_format() //将多媒体文件的信息打印出来

处理流程：
解复用-> 获取流-> 读数据包 -> 释放资源

程序内容：

#include<libavutil/log.h>
#include<libavformat/avformat.h>

int main (int argc,char *argv[]){
    int ret;
    AVFormatContext *fmt_ctx = NULL;
    av_log_set_level(AV_LOG_INFO);
    av_register_all();
    ret = avformat_open_input(&fmt_ctx,"./input.mp4",NULL,NULL);
    if(ret<0){
        av_log(NULL,AV_LOG_ERROR,"fail open input input.mp4");
        return -1;
    }
    av_dump_format(fmt_ctx, 0, "./test.mp4",0);
    avformat_close_input(&fmt_ctx);
    return 0;
}

使用命令编译： clang -g -o mediainfo mediainfo.c pkg-config --libs libavutil libavformat
运行程序：./mediainfo

5.FFmpeg 抽取音频数据

av_init_packet() //初始化一个数据包结构体
av_find_best_stream() //在多媒体文件中找到最好的一路流
av_read_frame()/av_packet_unref() //读取流中的数据包--释放frame的引用计数器

程序内容：(可能会编译不过)

#include<libavutil/log.h>
#include<libavformat/avformat.h>

int main (int argc,char *argv[]){
    int ret;
    char * src = NULL;
    char * dst = NULL;
    AVFormatContext *fmt_ctx = NULL;
    av_log_set_level(AV_LOG_INFO);
    av_register_all();

    //1.read two params
    if(argc<3){
        av_log(NULL,AV_LOG_ERROR,"the count of params should be more than three !\n");
    }
    src = argv[1];
    dst = argv[2];

    if(!src || !dst){
        av_log(NULL,AV_LOG_ERROR,"souce input or destion input is null\n");
        return -1;
    }
    ret = avformat_open_input(&fmt_ctx,src,NULL,NULL);
    if(ret<0){
        av_log(NULL,AV_LOG_ERROR,"fail open input input.mp4\n");
        return -1;
    }
    FILE *dst_fd = fopen(dst,"wb");
    if(!dst_fd){
        av_log(NULL,AV_LOG_ERROR,"can't open output file \n");
        avformat_close_input(&fmt_ctx);
        return -1;
    }
    //打印输入视频信息
    av_dump_format(fmt_ctx, 0, src,0);
    //2.get best stream
    ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);

    if(ret<0){
        av_log(NULL,AV_LOG_ERROR,"find best stream error\n"); 
        avformat_close_input(&fmt_ctx);
        fclose(dst_fd);
        return -1;
    }
    //3.write audio data for aac
    AVPacket pkt;
    int audio_index = ret;  //第35行拿到音频流的index
    av_init_packet(&pkt);
    while(av_read_frame(fmt_ctx,&pkt)>=0){
        if(pkt.stream_index == audio_index){
            //添加adts头
            char adts_header_buf[7];
            adts_header(adts_header_buf,pkt.size); 
            fwrite(adts_header_buf,1,7,dst_fd);
            //将音频数据写入文件
            int len = fwrite(pkt.data, 1, pkt.size, dst_fd);
            if(len != pkt.size){
                av_log(NULL,AV_LOG_WARNING,"waring write audio info error\n");
            }
        }
        av_packet_unref(&pkt);
    }
    
    avformat_close_input(&fmt_ctx);
    if(dst_fd){
        //关闭输出文件的写操作；
        fclose(dst_fd);
    }

    return 0;
}

使用命令编译：clang -g -o extra_audio extra_audio.c pkg-config --libs -liavutil avformat
运行程序：./extra_audio input.mp4 output.aac

6.FFmpeg 抽取 H264数据

程序内容：

#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avio.h>
#include <libavformat/avformat.h>

#ifndef AV_WB32
#   define AV_WB32(p, val) do {                 \
        uint32_t d = (val);                     \
        ((uint8_t*)(p))[3] = (d);               \
        ((uint8_t*)(p))[2] = (d)>>8;            \
        ((uint8_t*)(p))[1] = (d)>>16;           \
        ((uint8_t*)(p))[0] = (d)>>24;           \
    } while(0)
#endif

#ifndef AV_RB16
#   define AV_RB16(x)                           \
    ((((const uint8_t*)(x))[0] << 8) |          \
      ((const uint8_t*)(x))[1])
#endif

static int alloc_and_copy(AVPacket *out,
                          const uint8_t *sps_pps, uint32_t sps_pps_size,
                          const uint8_t *in, uint32_t in_size)
{
    uint32_t offset         = out->size;
    uint8_t nal_header_size = offset ? 3 : 4;
    int err;

    err = av_grow_packet(out, sps_pps_size + in_size + nal_header_size);
    if (err < 0)
        return err;

    if (sps_pps)
        memcpy(out->data + offset, sps_pps, sps_pps_size);
    memcpy(out->data + sps_pps_size + nal_header_size + offset, in, in_size);
    if (!offset) {
        AV_WB32(out->data + sps_pps_size, 1);
    } else {
        (out->data + offset + sps_pps_size)[0] =
        (out->data + offset + sps_pps_size)[1] = 0;
        (out->data + offset + sps_pps_size)[2] = 1;
    }

    return 0;
}

int h264_extradata_to_annexb(const uint8_t *codec_extradata, const int codec_extradata_size, AVPacket *out_extradata, int padding)
{
    uint16_t unit_size;
    uint64_t total_size                 = 0;
    uint8_t *out                        = NULL, unit_nb, sps_done = 0,
             sps_seen                   = 0, pps_seen = 0, sps_offset = 0, pps_offset = 0;
    const uint8_t *extradata            = codec_extradata + 4;
    static const uint8_t nalu_header[4] = { 0, 0, 0, 1 };
    int length_size = (*extradata++ & 0x3) + 1; // retrieve length coded size, 用于指示表示编码数据长度所需字节数

    sps_offset = pps_offset = -1;

    /* retrieve sps and pps unit(s) */
    unit_nb = *extradata++ & 0x1f; /* number of sps unit(s) */
    if (!unit_nb) {
        goto pps;
    }else {
        sps_offset = 0;
        sps_seen = 1;
    }

    while (unit_nb--) {
        int err;

        unit_size   = AV_RB16(extradata);
        total_size += unit_size + 4;
        if (total_size > INT_MAX - padding) {
            av_log(NULL, AV_LOG_ERROR,
                   "Too big extradata size, corrupted stream or invalid MP4/AVCC bitstream\n");
            av_free(out);
            return AVERROR(EINVAL);
        }
        if (extradata + 2 + unit_size > codec_extradata + codec_extradata_size) {
            av_log(NULL, AV_LOG_ERROR, "Packet header is not contained in global extradata, "
                   "corrupted stream or invalid MP4/AVCC bitstream\n");
            av_free(out);
            return AVERROR(EINVAL);
        }
        if ((err = av_reallocp(&out, total_size + padding)) < 0)
            return err;
        memcpy(out + total_size - unit_size - 4, nalu_header, 4);
        memcpy(out + total_size - unit_size, extradata + 2, unit_size);
        extradata += 2 + unit_size;
pps:
        if (!unit_nb && !sps_done++) {
            unit_nb = *extradata++; /* number of pps unit(s) */
            if (unit_nb) {
                pps_offset = total_size;
                pps_seen = 1;
            }
        }
    }

    if (out)
        memset(out + total_size, 0, padding);

    if (!sps_seen)
        av_log(NULL, AV_LOG_WARNING,
               "Warning: SPS NALU missing or invalid. "
               "The resulting stream may not play.\n");

    if (!pps_seen)
        av_log(NULL, AV_LOG_WARNING,
               "Warning: PPS NALU missing or invalid. "
               "The resulting stream may not play.\n");

    out_extradata->data      = out;
    out_extradata->size      = total_size;

    return length_size;
}

int h264_mp4toannexb(AVFormatContext *fmt_ctx, AVPacket *in, FILE *dst_fd)
{

    AVPacket *out = NULL;
    AVPacket spspps_pkt;

    int len;
    uint8_t unit_type;
    int32_t nal_size;
    uint32_t cumul_size    = 0;
    const uint8_t *buf;
    const uint8_t *buf_end;
    int            buf_size;
    int ret = 0, i;

    out = av_packet_alloc();

    buf      = in->data;
    buf_size = in->size;
    buf_end  = in->data + in->size;

    do {
        ret= AVERROR(EINVAL);
        if (buf + 4 > buf_end)
            goto fail;

        for (nal_size = 0, i = 0; i<4; i++)
            nal_size = (nal_size << 8) | buf[i];

        buf += 4;
        unit_type = *buf & 0x1f;

        if (nal_size > buf_end - buf || nal_size < 0)
            goto fail;

        if (unit_type == 5) {

            h264_extradata_to_annexb( fmt_ctx->streams[in->stream_index]->codec->extradata,
                                      fmt_ctx->streams[in->stream_index]->codec->extradata_size,
                                      &spspps_pkt,
                                      AV_INPUT_BUFFER_PADDING_SIZE);

            if ((ret=alloc_and_copy(out,
                               spspps_pkt.data, spspps_pkt.size,
                               buf, nal_size)) < 0)
            {
                goto fail;
            }

        /* if only SPS has been seen, also insert PPS */
        }
         else {
            if ((ret=alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
                goto fail;
        }


        len = fwrite( out->data, 1, out->size, dst_fd);
        if(len != out->size){
            av_log(NULL, AV_LOG_DEBUG, "warning, length of writed data isn't equal pkt.size(%d, %d)\n",
                    len,
                    out->size);
        }
        fflush(dst_fd);

next_nal:
        buf        += nal_size;
        cumul_size += nal_size + 4;//s->length_size;
    } while (cumul_size < buf_size);
fail:
    av_packet_free(&out);

    return ret;
}

int main(int argc, char *argv[])
{
    int err_code;
    char errors[1024];
    char *src_filename = NULL;
    char *dst_filename = NULL;
    FILE *dst_fd = NULL;
    int video_stream_index = -1;
    AVFormatContext *fmt_ctx = NULL;
    AVPacket pkt;

    av_log_set_level(AV_LOG_DEBUG);

    if(argc < 3){
        av_log(NULL, AV_LOG_DEBUG, "the count of parameters should be more than three!\n");
        return -1;
    }

    src_filename = argv[1];
    dst_filename = argv[2];

    if(src_filename == NULL || dst_filename == NULL){
        av_log(NULL, AV_LOG_ERROR, "src or dts file is null, plz check them!\n");
        return -1;
    }

    /*register all formats and codec*/
    av_register_all();

    dst_fd = fopen(dst_filename, "wb");
    if (!dst_fd) {
        av_log(NULL, AV_LOG_DEBUG, "Could not open destination file %s\n", dst_filename);
        return -1;
    }

    /*open input media file, and allocate format context*/
    if((err_code = avformat_open_input(&fmt_ctx, src_filename, NULL, NULL)) < 0){
        av_strerror(err_code, errors, 1024);
        av_log(NULL, AV_LOG_DEBUG, "Could not open source file: %s, %d(%s)\n",
               src_filename,
               err_code,
               errors);
        return -1;
    }

    /*dump input information*/
    av_dump_format(fmt_ctx, 0, src_filename, 0);

    /*initialize packet*/
    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    /*find best video stream*/
    video_stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
    if(video_stream_index < 0){
        av_log(NULL, AV_LOG_DEBUG, "Could not find %s stream in input file %s\n",
               av_get_media_type_string(AVMEDIA_TYPE_VIDEO),
               src_filename);
        return AVERROR(EINVAL);
    }
    /*read frames from media file*/
    while(av_read_frame(fmt_ctx, &pkt) >=0 ){
        if(pkt.stream_index == video_stream_index){
            h264_mp4toannexb(fmt_ctx, &pkt, dst_fd);
        }
        av_packet_unref(&pkt);
    }

    /*close input media file*/
    avformat_close_input(&fmt_ctx);
    if(dst_fd) {
        fclose(dst_fd);
    }

    return 0;
}

使用命令编译：
clang -g -o extr_video extr_video.c pkg-config --libs libavutil libavformat
运行程序：
./extr_video input.mp4 inpu4.h264
ffplay input.h264

7.ffmpeg 将mp4转成flv

avformat_alloc_output_context2() //多媒体输出文件输的的上下文
avformat_free_context() //释放多媒体输出上下文
avformat_new_stream() //输出的多媒体文件中输出新的流
avcodec_parameters_copy() //拷贝多媒体参数
avformat_write_header() //多媒体文件头
av_write_frame()/av_interleaved_write_frame() // 向多媒体文件写入frame数据
av_write_trailer() //写入多媒体文件尾部信息

程序内容：

#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>

static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *tag)
{
    AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;

    printf("%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
           tag,
           av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
           av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
           av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),
           pkt->stream_index);
}

int main(int argc, char **argv)
{
    AVOutputFormat *ofmt = NULL;
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    const char *in_filename, *out_filename;
    int ret, i;
    int stream_index = 0;
    int *stream_mapping = NULL;
    int stream_mapping_size = 0;

    if (argc < 3) {
        printf("usage: %s input output\n"
               "API example program to remux a media file with libavformat and libavcodec.\n"
               "The output format is guessed according to the file extension.\n"
               "\n", argv[0]);
        return 1;
    }

    in_filename  = argv[1];
    out_filename = argv[2];

    av_register_all();

    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
        fprintf(stderr, "Could not open input file '%s'", in_filename);
        goto end;
    }

    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        fprintf(stderr, "Failed to retrieve input stream information");
        goto end;
    }

    av_dump_format(ifmt_ctx, 0, in_filename, 0);

    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }

    stream_mapping_size = ifmt_ctx->nb_streams;
    stream_mapping = av_mallocz_array(stream_mapping_size, sizeof(*stream_mapping));
    if (!stream_mapping) {
        ret = AVERROR(ENOMEM);
        goto end;
    }

    ofmt = ofmt_ctx->oformat;

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        AVStream *out_stream;
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVCodecParameters *in_codecpar = in_stream->codecpar;

        if (in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO &&
            in_codecpar->codec_type != AVMEDIA_TYPE_VIDEO &&
            in_codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE) {
            stream_mapping[i] = -1;
            continue;
        }

        stream_mapping[i] = stream_index++;

        out_stream = avformat_new_stream(ofmt_ctx, NULL);
        if (!out_stream) {
            fprintf(stderr, "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }

        ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar);
        if (ret < 0) {
            fprintf(stderr, "Failed to copy codec parameters\n");
            goto end;
        }
        out_stream->codecpar->codec_tag = 0;
    }
    av_dump_format(ofmt_ctx, 0, out_filename, 1);

    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "Could not open output file '%s'", out_filename);
            goto end;
        }
    }

    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error occurred when opening output file\n");
        goto end;
    }

    while (1) {
        AVStream *in_stream, *out_stream;

        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;

        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        if (pkt.stream_index >= stream_mapping_size ||
            stream_mapping[pkt.stream_index] < 0) {
            av_packet_unref(&pkt);
            continue;
        }

        pkt.stream_index = stream_mapping[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];
        log_packet(ifmt_ctx, &pkt, "in");

        /* copy packet */
        pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
        log_packet(ofmt_ctx, &pkt, "out");

        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error muxing packet\n");
            break;
        }
        av_packet_unref(&pkt);
    }

    av_write_trailer(ofmt_ctx);
end:

    avformat_close_input(&ifmt_ctx);

    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

    av_freep(&stream_mapping);

    if (ret < 0 && ret != AVERROR_EOF) {
        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
        return 1;
    }

    return 0;
}

使用命令编译：
clang -g -o remuxing remuxing pkg-config --libs libavutil libavformat
运行程序：
./remuxing input.mp4 output.flv
ffplay output.flv

8.FFmpeg音视频裁剪

程序内容：

#include <stdlib.h>
#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>

static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *tag)
{
    AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;

    printf("%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
           tag,
           av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
           av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
           av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),
           pkt->stream_index);
}

int cut_video(double from_seconds, double end_seconds, const char* in_filename, const char* out_filename) {
    AVOutputFormat *ofmt = NULL;
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    int ret, i;

    av_register_all();

    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
        fprintf(stderr, "Could not open input file '%s'", in_filename);
        goto end;
    }

    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        fprintf(stderr, "Failed to retrieve input stream information");
        goto end;
    }

    av_dump_format(ifmt_ctx, 0, in_filename, 0);

    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }

    ofmt = ofmt_ctx->oformat;

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
        if (!out_stream) {
            fprintf(stderr, "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }

        ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
        if (ret < 0) {
            fprintf(stderr, "Failed to copy context from input to output stream codec context\n");
            goto end;
        }
        out_stream->codec->codec_tag = 0;
        if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
            out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }
    av_dump_format(ofmt_ctx, 0, out_filename, 1);

    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "Could not open output file '%s'", out_filename);
            goto end;
        }
    }

    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error occurred when opening output file\n");
        goto end;
    }

    //    int indexs[8] = {0};


    //    int64_t start_from = 8*AV_TIME_BASE;
    ret = av_seek_frame(ifmt_ctx, -1, from_seconds*AV_TIME_BASE, AVSEEK_FLAG_ANY);
    if (ret < 0) {
        fprintf(stderr, "Error seek\n");
        goto end;
    }

    int64_t *dts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
    memset(dts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);
    int64_t *pts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
    memset(pts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);

    while (1) {
        AVStream *in_stream, *out_stream;

        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;

        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];

        log_packet(ifmt_ctx, &pkt, "in");

        if (av_q2d(in_stream->time_base) * pkt.pts > end_seconds) {
            av_free_packet(&pkt);
            break;
        }

        if (dts_start_from[pkt.stream_index] == 0) {
            dts_start_from[pkt.stream_index] = pkt.dts;
            printf("dts_start_from: %s\n", av_ts2str(dts_start_from[pkt.stream_index]));
        }
        if (pts_start_from[pkt.stream_index] == 0) {
            pts_start_from[pkt.stream_index] = pkt.pts;
            printf("pts_start_from: %s\n", av_ts2str(pts_start_from[pkt.stream_index]));
        }

        /* copy packet */
        pkt.pts = av_rescale_q_rnd(pkt.pts - pts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.dts = av_rescale_q_rnd(pkt.dts - dts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        if (pkt.pts < 0) {
            pkt.pts = 0;
        }
        if (pkt.dts < 0) {
            pkt.dts = 0;
        }
        pkt.duration = (int)av_rescale_q((int64_t)pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
        log_packet(ofmt_ctx, &pkt, "out");
        printf("\n");

        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error muxing packet\n");
            break;
        }
        av_free_packet(&pkt);
    }
    free(dts_start_from);
    free(pts_start_from);

    av_write_trailer(ofmt_ctx);
end:

    avformat_close_input(&ifmt_ctx);

    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

    if (ret < 0 && ret != AVERROR_EOF) {
        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
        return 1;
    }

    return 0;
}

int main(int argc, char *argv[]){
    if(argc < 5){
        fprintf(stderr, "Usage: \
                command startime, endtime, srcfile, outfile");
        return -1;
    }

    double startime = atoi(argv[1]);
    double endtime = atoi(argv[2]);
    cut_video(startime, endtime, argv[3], argv[4]);

    return 0;
}

使用命令编译：
运行程序：