1、ffmpeg的日志打印

include<libavutil/log.h>
av_log_set_level(AV_LOG_DEBUG)
av_log(NULL, AV_LOG_INFO,"...");AV_LOG_ERROR
AV_LOG_WARNING
AV_LOG_INFO
AV_LOG_DEBUG

具体例子：
ff_log.c :

#include<stdio.h>
#include<libavutil/log.h>int main(int argc, char *argv[]){av_log_set_level(AV_LOG_INFO);av_log(NULL, AV_LOG_DEBUG, "Hello world:%s%d\n","aaa",10);av_log(NULL, AV_LOG_INFO, "Hello world INFO!\n");av_log(NULL, AV_LOG_ERROR, "Hello world ERROR!\n");return 0;
}

vim ff_log.c clang -g -o ff_log ff_log.c -I/usr/local/ffmpeg/include -L/usr/local/ffmpeg/lib -lavutil
或者：
clang -g -o ff_log ff_log.c `pkg-config --cflags --libs libavutil`./ff_log
Hello world INFO!
Hello world ERROR!

mac中，使用第二种方式编译链接时报错如下：

Package libavutil was not found in the pkg-config search path.
Perhaps you should add the directory containing `libavutil.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libavutil' found
ff_log.c:2:9: fatal error: 'libavutil/log.h' file not found
#include<libavutil/log.h>^~~~~~~~~~~~~~~~~
1 error generated.

解决办法如下：

vim ~/.bash_profile
source ~/.bash_profile

在文件中添加最后两行export：

# HomeBrew
export HOMEBREW_BOTTLE_DOMAIN=https://mirrors.ustc.edu.cn/homebrew-bottles
export PATH="/usr/local/bin:$PATH"
export PATH="/usr/local/sbin:$PATH"
export PATH="/usr/local/ffmpeg/bin:$PATH"export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/ffmpeg/lib/pkgconfig
export LD_LIBRARY_PATH=$LIB_LIBRARY_PATH:/usr/local/ffmpeg/lib
# HomeBrew END

2、ffmpeg文件与目录操作

文件删除与重命名：

avpriv_io_delete()avpriv_io_move()

ffmpeg_file.c:

#include<stdio.h>
#include<libavutil/log.h>
#include<libavformat/avformat.h>int main(int argc, char* argv[]){int ret;// 重命名文件ret = avpriv_io_move("111.txt", "222.txt");if(ret < 0){av_log(NULL, AV_LOG_ERROR, "Failed to rename\n");return -1;}av_log(NULL, AV_LOG_INFO, "Success to rename\n");// 删除文件// urlret = avpriv_io_delete("./mytestfile.txt");if(ret < 0){av_log(NULL, AV_LOG_ERROR, "Fail to delete file mytestfile.txt\n");return -1;}av_log(NULL, AV_LOG_INFO, "Success to delete mytestfile.txt\n");return 0;
}

编译运行：

ffmpeg_file % clang -g -o ffmpeg_mov_del ffmpeg_file.c `pkg-config --cflags --libs libavutil --libs libavformat`
./ffmpeg_mov_del

3、ffmpeg操作目录

avio_open_dir()avio_read_dir()avio_close_dir()AVIODirContext 操作目录的上下文AVIODirEntry    目录项 存放文件名，文件大小等信息

实现一个简单的ls命令：

ffmpeg_file_list.c:

#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, "Cannot open dir:%s\n", av_err2str(ret));}while(1){ret = avio_read_dir(ctx, &entry);if(ret < 0){av_log(NULL, AV_LOG_ERROR, "Cannot read dir:%s\n", 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;
}

编译运行：

clang -g -o ffmpeg_list ffmpeg_file_list.c `pkg-config --cflags --libs libavutil --libs libavformat`./ffmpeg_list6148 .DS_Store 96 ffmpeg_del.dSYM 49848 ffmpeg_del 0 222.txt 536 ffmpeg_file.c 689 ffmpeg_file_list.c 50408 ffmpeg_list 96 ffmpeg_list.dSYM

4、ffmpeg处理流数据

4.1 概念

多媒体文件其实就是容器，在容器中有很多流（流Stream/轨Track）；
从流中读出的数据称为包；
在一个包中包含着一个或多个帧。

4.2 重要结构体

AVFormatContext  格式上下文
AVStream    流
AVPacket    包

4.3 FFmpeg操作流数据的基本步骤

解复用打开容器
获取流拿到容器中的流
读数据包从流中取出一个个数据包
释放资源做完逻辑操作后释放资源

5、实战

5.1 打印音视频信息

新版本ffmpeg中弃用了这个函数：av_register_all() 所有ffmpeg代码开始前都得先调用此apiavformat_open_input() 和 avformat_close_input()  成对出现
打开多媒体文件，输出结构体AVFormatContext，借助这个格式上下文获取参数信息，最后关闭多媒体文件av_dump_format() 打印多媒体文件的meta信息

vim mediainfo.c输入内容如下：
#include<libavutil/log.h>
#include<libavformat/avformat.h>int main(int argc, char* argv[])
{int ret;AVFormatContext *fmt_ctx = NULL; // 定义上下文av_log_set_level(AV_LOG_INFO); // 设置日志级别//av_register_all(); // 注册多媒体格式协议，新版本ffmpeg中弃用了这个函数avformat_open_input(&fmt_ctx,"./test.mp4", NULL, NULL); // 打开多媒体文件 第3个参数NULL:指定输入格式，默认文件后缀名if(ret<0){ // 如果打开失败，就打印日志信息并退出av_log(NULL, AV_LOG_ERROR, "Can't open file: %s\n",av_err2str(ret));return -1;}// 打开成功，进入这里，执行下面的逻辑av_dump_format(fmt_ctx, 0, "./test.mp4", 0); // 打印多诶题文件的meta信息  no2填0记住即可；no4填0表示是输入文件，如果输出文件填1avformat_close_input(&fmt_ctx); // 关闭多媒体文件return 0;
}

编译：

clang -g -o mediainfo mediainfo.c `pkg-config --cflags --libs libavutil --libs libavformat`
有个警告：
mediainfo.c:11:2: warning: 'avcodec_register_all' is deprecated

执行：

 ./mediainfoInput #0, mov,mp4,m4a,3gp,3g2,mj2, from './test.mp4':Metadata:major_brand     : isomminor_version   : 512compatible_brands: isomiso2avc1mp41comment         : vid:v0300fa50000c08eg9qcf5vi1hpn9gfgencoder         : Lavf58.20.100Duration: 00:00:10.94, bitrate: N/AStream #0:0(und): Video: h264 (avc1 / 0x31637661), none, 720x1280, 1174 kb/s, SAR 1:1 DAR 9:16, 29.82 fps, 30 tbr, 15360 tbn (default)Metadata:handler_name    : VideoHandlerStream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, 2 channels, 128 kb/s (default)Metadata:handler_name    : SoundHandler

5.2 抽取音频数据

av_init_packet() 初始化的数据包av_find_best_stream() 找到想要拿到的最好的一路流av_read_frame() / av_packet_unref()  read获取流中的数据包，做一些处理，本例是写入aac文件；
每次用read读取数据包，会增加引用计数，使用unref可以释放引用计数，让ffmpeg自动释放包，避免内存泄漏

使用课程中的代码抽取音频：

#include<stdio.h>
#include<libavutil/log.h>
#include<libavformat/avformat.h>
#include <libavformat/avio.h>#define ADTS_HEADER_LEN  7;void adts_header(char *szAdtsHeader, int dataLen){int audio_object_type = 2; int sampling_frequency_index = 7;int channel_config = 2;int adtsLen = dataLen + 7;szAdtsHeader[0] = 0xff;         //syncword:0xfff                          高8bitsszAdtsHeader[1] = 0xf0;         //syncword:0xfff                          低4bitsszAdtsHeader[1] |= (0 << 3);    //MPEG Version:0 for MPEG-4,1 for MPEG-2  1bitszAdtsHeader[1] |= (0 << 1);    //Layer:0                                 2bits szAdtsHeader[1] |= 1;           //protection absent:1                     1bitszAdtsHeader[2] = (audio_object_type - 1)<<6;            //profile:audio_object_type - 1                      2bitsszAdtsHeader[2] |= (sampling_frequency_index & 0x0f)<<2; //sampling frequency index:sampling_frequency_index  4bits szAdtsHeader[2] |= (0 << 1);                             //private bit:0                                      1bitszAdtsHeader[2] |= (channel_config & 0x04)>>2;           //channel configuration:channel_config               高1bitszAdtsHeader[3] = (channel_config & 0x03)<<6;     //channel configuration:channel_config      低2bitsszAdtsHeader[3] |= (0 << 5);                      //original：0                               1bitszAdtsHeader[3] |= (0 << 4);                      //home：0                                   1bitszAdtsHeader[3] |= (0 << 3);                      //copyright id bit：0                       1bit  szAdtsHeader[3] |= (0 << 2);                      //copyright id start：0                     1bitszAdtsHeader[3] |= ((adtsLen & 0x1800) >> 11);           //frame length：value   高2bitsszAdtsHeader[4] = (uint8_t)((adtsLen & 0x7f8) >> 3);     //frame length:value    中间8bitsszAdtsHeader[5] = (uint8_t)((adtsLen & 0x7) << 5);       //frame length:value    低3bitsszAdtsHeader[5] |= 0x1f;                                 //buffer fullness:0x7ff 高5bitsszAdtsHeader[6] = 0xfc;
}int main(int argc, char* argv[])
{int ret;int len;int audio_index;char* src = NULL;char* dst = NULL;AVPacket pkt;AVFormatContext *fmt_ctx = NULL; // 定义上下文av_log_set_level(AV_LOG_INFO); // 设置日志级别// 1:read two params from consoleif(argc<3){av_log(NULL, AV_LOG_ERROR, "the count of params should be 3.\n");return -1;}   src = argv[1];dst = argv[2];if(!src || !dst){av_log(NULL, AV_LOG_ERROR, "src or dst is null!\n");return -1;}ret = avformat_open_input(&fmt_ctx, src, NULL, NULL); // 打开多媒文件if(ret<0){ // 如果打开失败，就打印日志信息并退出av_log(NULL, AV_LOG_ERROR, "Can't open file: %s\n",av_err2str(ret));return -1;}// 打开成功，进入这里，执行下面的逻辑FILE* dst_fd = fopen(dst, "wb");if(!dst_fd){av_log(NULL, AV_LOG_ERROR, "Can't open out file!\n");avformat_close_input(&fmt_ctx); // 此时输入流已打开了，需要关闭return -1;}av_dump_format(fmt_ctx, 0, src, 0); // 打印多诶题文件的meta信息  no2填0记住即可；no4填0表示是输入文件，如果输出文件填1// 2:get streamret = av_find_best_stream(fmt_ctx/*上下文*/, AVMEDIA_TYPE_AUDIO/*想要抽取的流的类型，音频流*/, -1/*流的索引号，此处不知道*/,-1/*音频流对应的视频流的索引号，此处不关心*/,NULL/*流的编解码器，不关心*/,0/*flag,一些标准，不关心*/ );       if(ret<0){av_log(NULL, AV_LOG_ERROR, "Cannot find the best stream!\n");avformat_close_input(&fmt_ctx);fclose(dst_fd);return -1;}audio_index = ret;av_init_packet(&pkt);while(av_read_frame(fmt_ctx, &pkt) >= 0){if(pkt.stream_index == audio_index){// 生成adts头，并写入文件char adts_header_buf[7];adts_header(adts_header_buf, pkt.size);fwrite(adts_header_buf, 1, 7, dst_fd);// 3:write audio data to aac filelen = fwrite(pkt.data/*待存内容*/, 1/*逐个字节写入*/, pkt.size/*写入多少个字节*/, dst_fd/*写入哪个文件*/);if(len != pkt.size){av_log(NULL, AV_LOG_WARNING, "warning, length of data is not equal size of pkt!");}}av_packet_unref(&pkt); // 不管是不是最好的那路流，到这里都要释放}avformat_close_input(&fmt_ctx);if(dst_fd){fclose(dst_fd);}avformat_close_input(&fmt_ctx); // 关闭多媒体文件return 0;
}

为什么我使用课程中的程序无法成功抽取AAC音频？
利用ffmpeg中的api实现音频抽取

#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avio.h>
#include <libavformat/avformat.h>#define ERROR_STR_SIZE 1024int main(int argc, char *argv[])
{int err_code;char errors[1024];char *src_filename = NULL;char *dst_filename = NULL;FILE *dst_fd = NULL;int audio_stream_index = -1;int len;AVFormatContext *ofmt_ctx = NULL;AVOutputFormat *output_fmt = NULL;AVStream *in_stream = NULL;AVStream *out_stream = NULL;AVFormatContext *fmt_ctx = NULL;//AVFrame *frame = 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_DEBUG, "src or dts file is null, plz check them!\n");return -1;}/*register all formats and codec*/av_register_all();/*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;}/*retrieve audio stream*/if((err_code = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {av_strerror(err_code, errors, 1024);av_log(NULL, AV_LOG_DEBUG, "failed to find stream information: %s, %d(%s)\n",src_filename,err_code,errors);return -1;}/*dump input information*/av_dump_format(fmt_ctx, 0, src_filename, 0);in_stream = fmt_ctx->streams[1];AVCodecParameters *in_codecpar = in_stream->codecpar;if(in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO){av_log(NULL, AV_LOG_ERROR, "The Codec type is invalid!\n");exit(1);}//out fileofmt_ctx = avformat_alloc_context();output_fmt = av_guess_format(NULL, dst_filename, NULL);if(!output_fmt){av_log(NULL, AV_LOG_DEBUG, "Cloud not guess file format \n");exit(1);}ofmt_ctx->oformat = output_fmt;out_stream = avformat_new_stream(ofmt_ctx, NULL);if(!out_stream){av_log(NULL, AV_LOG_DEBUG, "Failed to create out stream!\n");exit(1);}if(fmt_ctx->nb_streams<2){av_log(NULL, AV_LOG_ERROR, "the number of stream is too less!\n");exit(1);}if((err_code = avcodec_parameters_copy(out_stream->codecpar, in_codecpar)) < 0 ){av_strerror(err_code, errors, ERROR_STR_SIZE);av_log(NULL, AV_LOG_ERROR,"Failed to copy codec parameter, %d(%s)\n",err_code, errors);}out_stream->codecpar->codec_tag = 0;if((err_code = avio_open(&ofmt_ctx->pb, dst_filename, AVIO_FLAG_WRITE)) < 0) {av_strerror(err_code, errors, 1024);av_log(NULL, AV_LOG_DEBUG, "Could not open file %s, %d(%s)\n",dst_filename,err_code,errors);exit(1);}/*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;}*//*dump output information*/av_dump_format(ofmt_ctx, 0, dst_filename, 1);/*frame = av_frame_alloc();if(!frame){av_log(NULL, AV_LOG_DEBUG, "Could not allocate frame\n");return AVERROR(ENOMEM);}*//*initialize packet*/av_init_packet(&pkt);pkt.data = NULL;pkt.size = 0;/*find best audio stream*/audio_stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);if(audio_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_AUDIO),src_filename);return AVERROR(EINVAL);}if (avformat_write_header(ofmt_ctx, NULL) < 0) {av_log(NULL, AV_LOG_DEBUG, "Error occurred when opening output file");exit(1);}/*read frames from media file*/while(av_read_frame(fmt_ctx, &pkt) >=0 ){if(pkt.stream_index == audio_stream_index){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 = pkt.pts;pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);pkt.pos = -1;pkt.stream_index = 0;av_interleaved_write_frame(ofmt_ctx, &pkt);av_packet_unref(&pkt);}}av_write_trailer(ofmt_ctx);/*close input media file*/avformat_close_input(&fmt_ctx);if(dst_fd) {fclose(dst_fd);}avio_close(ofmt_ctx->pb);return 0;
}

5.3 抽取视频数据

Start code 在每一帧前面的关键字
将一帧一帧数据区分开：可以在每一帧前面加该帧的长度；也可以在每一帧前面加关键字或特征码；SPS / PPS 解码的视频帧的参数 每个关键帧前加codec->extradata 获取SPS和PPS是从编码器的扩展数据中获取，而非从数据包中

目的：
在每一个帧的前面增加Start Code特征码；
在每个关键帧前面增加SPS和PPS，同时也增加了特征码。

5.4 将MP4转成FLV格式

avformat_alloc_output_context2() / avformat_free_context()avformat_new_stream()avcodec_parameters_copy()avformat_write_header() 生成多媒体文件头av_write_frame() / av_interleaved_write_frame()av_write_trailer()

可以将test.mpt 转换成 test.flv

#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];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 write_header\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;
}

5.5 从MP4截取一段视频

av_seek_frame()

截取时，./cut 5 15 srcVideo toVideo将视频srcVideo的第5秒到第15秒存入toVideo

#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, NULL);if (!out_stream) {fprintf(stderr, "Failed allocating output stream\n");ret = AVERROR_UNKNOWN;goto end;}ret = avcodec_parameters_copy(out_stream->codecpar, in_stream->codecpar);if (ret < 0) {fprintf(stderr, "Failed to copy context from input to output stream codec context\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;}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_packet_unref(&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;}if(pkt.pts < pkt.dts) continue;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_packet_unref(&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;
}

5.6 一个简单的小咖秀

将两个媒体文件中分别抽取音频与视频
将音频与视频轨合并成一个新文件
对音频与视频轨进行裁剪

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