ffmpeg学习日记11-使用ffmpeg将视频格式转换为视频编码h264格式

前言

将一种视频格式，例如mp4的视频，转换成对饮的视频编码h264格式的文件，实现功能的方式有两种，一种是调用ffmpeg工具，通过命令行进行转换，另一种是通过调用ffmpeg的函数，自己写代码进行转换，我们现在的要用第二种实现来完成这个功能。

ffmpeg工具源码分析

ffmpeg源码版本：4.1
通过全文检索，确定生成ffmpeg工具的Makefile是在/fftools/Makefile中，makefile的内容比较简单，不做过多分析

先看fftools/ffmpeg.c文件中的main：

int main(int argc, char **argv)
{int i, ret;BenchmarkTimeStamps ti;init_dynload();		//对应win平台的dll加载register_exit(ffmpeg_cleanup);	//相当于c++的析构，这里用了回调，用来释放空间setvbuf(stderr,NULL,_IONBF,0); /* win32 runtime needs this */  //设置环境变量av_log_set_flags(AV_LOG_SKIP_REPEATED);parse_loglevel(argc, argv, options);if(argc>1 && !strcmp(argv[1], "-d")){run_as_daemon=1;av_log_set_callback(log_callback_null);argc--;argv++;}#if CONFIG_AVDEVICEavdevice_register_all();			//驱动设备注册
#endifavformat_network_init();			//网络驱动初始化show_banner(argc, argv, options);/* parse options and open all input/output files */ret = ffmpeg_parse_options(argc, argv);			//参数解析if (ret < 0)exit_program(1);if (nb_output_files <= 0 && nb_input_files == 0) {show_usage();av_log(NULL, AV_LOG_WARNING, "Use -h to get full help or, even better, run 'man %s'\n", program_name);exit_program(1);}/* file converter / grab */if (nb_output_files <= 0) {av_log(NULL, AV_LOG_FATAL, "At least one output file must be specified\n");exit_program(1);}for (i = 0; i < nb_output_files; i++) {if (strcmp(output_files[i]->ctx->oformat->name, "rtp"))want_sdp = 0;}current_time = ti = get_benchmark_time_stamps();if (transcode() < 0)exit_program(1);if (do_benchmark) {int64_t utime, stime, rtime;current_time = get_benchmark_time_stamps();utime = current_time.user_usec - ti.user_usec;stime = current_time.sys_usec  - ti.sys_usec;rtime = current_time.real_usec - ti.real_usec;av_log(NULL, AV_LOG_INFO,"bench: utime=%0.3fs stime=%0.3fs rtime=%0.3fs\n",utime / 1000000.0, stime / 1000000.0, rtime / 1000000.0);}av_log(NULL, AV_LOG_DEBUG, "%"PRIu64" frames successfully decoded, %"PRIu64" decoding errors\n",decode_error_stat[0], decode_error_stat[1]);if ((decode_error_stat[0] + decode_error_stat[1]) * max_error_rate < decode_error_stat[1])exit_program(69);exit_program(received_nb_signals ? 255 : main_return_code);return main_return_code;
}

ffmpeg_parse_options函数在ffmpeg_opt.c文件中：

int ffmpeg_parse_options(int argc, char **argv)
{OptionParseContext octx;uint8_t error[128];int ret;memset(&octx, 0, sizeof(octx));/* split the commandline into an internal representation */ret = split_commandline(&octx, argc, argv, options, groups,FF_ARRAY_ELEMS(groups));if (ret < 0) {av_log(NULL, AV_LOG_FATAL, "Error splitting the argument list: ");goto fail;}/* apply global options */ret = parse_optgroup(NULL, &octx.global_opts);if (ret < 0) {av_log(NULL, AV_LOG_FATAL, "Error parsing global options: ");goto fail;}/* configure terminal and setup signal handlers */term_init();/* open input files */ret = open_files(&octx.groups[GROUP_INFILE], "input", open_input_file);if (ret < 0) {av_log(NULL, AV_LOG_FATAL, "Error opening input files: ");goto fail;}/* create the complex filtergraphs */ret = init_complex_filters();if (ret < 0) {av_log(NULL, AV_LOG_FATAL, "Error initializing complex filters.\n");goto fail;}/* open output files */ret = open_files(&octx.groups[GROUP_OUTFILE], "output", open_output_file);if (ret < 0) {av_log(NULL, AV_LOG_FATAL, "Error opening output files: ");goto fail;}check_filter_outputs();fail:uninit_parse_context(&octx);if (ret < 0) {av_strerror(ret, error, sizeof(error));av_log(NULL, AV_LOG_FATAL, "%s\n", error);}return ret;
}

个人理解

示例代码

函数释义

解码步骤

参考

• 最简单的基于FFMPEG的封装格式转换器（无编解码）
• FFmpeg音视频文件解封装实现
• RTSP再学习 – 利用FFmpeg 将 rtsp 获取H264裸流并保存到文件中
• 音视频数据处理（一）-H264/AVC视频码流分析
• 【音视频技术】AVC H264的一些基本概念和知识点
• 视音频数据处理入门：H.264视频码流解析