ffmpeg源代码：ffmpeg_parse_options()函数

ftools&＃xff0f;ffmpeg.c 文件&＃xff0c;包含ffmpeg指令信息&＃xff0c;其主函数如下:

int main(int argc, char **argv)
{int i, ret;BenchmarkTimeStamps ti;init_dynload();register_exit(ffmpeg_cleanup);setvbuf(stderr,NULL,_IONBF,0); /* win32 runtime needs this */av_log_set_flags(AV_LOG_SKIP_REPEATED);parse_loglevel(argc, argv, options);if(argc>1 && !strcmp(argv[1], "-d")){run_as_daemon&＃61;1;av_log_set_callback(log_callback_null);argc--;argv&＃43;&＃43;;}#if CONFIG_AVDEVICEavdevice_register_all();
#endifavformat_network_init();show_banner(argc, argv, options);/* parse options and open all input/output files */ret &＃61; f(argc, argv);if (ret <0)exit_program(1);if (nb_output_files <&＃61; 0 && nb_input_files &＃61;&＃61; 0) {show_usage();av_log(NULL, AV_LOG_WARNING, "Use -h to get full help or, even better, run &＃39;man %s&＃39;\n", program_name);exit_program(1);}/* file converter / grab */if (nb_output_files <&＃61; 0) {av_log(NULL, AV_LOG_FATAL, "At least one output file must be specified\n");exit_program(1);}for (i &＃61; 0; i ctx->oformat->name, "rtp"))want_sdp &＃61; 0;}current_time &＃61; ti &＃61; get_benchmark_time_stamps();if (transcode() <0)exit_program(1);if (do_benchmark) {int64_t utime, stime, rtime;current_time &＃61; get_benchmark_time_stamps();utime &＃61; current_time.user_usec - ti.user_usec;stime &＃61; current_time.sys_usec - ti.sys_usec;rtime &＃61; current_time.real_usec - ti.real_usec;av_log(NULL, AV_LOG_INFO,"bench: utime&＃61;%0.3fs stime&＃61;%0.3fs rtime&＃61;%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] &＃43; decode_error_stat[1]) * max_error_rate }

主函数中包含ffmpeg_parse_options()函数&＃xff0c;主要用于解析命令行参数&＃xff0c;其基本调用结构如下&＃xff1a;

解析过程中主要起作用的函数为split_commandline()函数&＃xff1a;

ret &＃61; split_commandline(&octx, argc, argv, options, groups,FF_ARRAY_ELEMS(groups));


OptionParseContext octx&＃xff0c;用来存储被解析后的数据&＃xff0c;全局参数&＃xff0c;输入输出参数 

typedef struct OptionParseContext {OptionGroup global_opts;OptionGroupList *groups;int nb_groups;/* parsing state */OptionGroup cur_group;
} OptionParseContext;

options参数定义在ffmpeg_opt.c中&＃xff0c;以下为其部分定义&＃xff1a;

const OptionDef options[] &＃61; {/* main options */CMDUTILS_COMMON_OPTIONS{ "f", HAS_ARG | OPT_STRING | OPT_OFFSET |OPT_INPUT | OPT_OUTPUT, { .off &＃61; OFFSET(format) },"force format", "fmt" },{ "y", OPT_BOOL, { &file_overwrite },"overwrite output files" },{ "n", OPT_BOOL, { &no_file_overwrite },"never overwrite output files" },{ "ignore_unknown", OPT_BOOL, { &ignore_unknown_streams },"Ignore unknown stream types" },{ "copy_unknown", OPT_BOOL | OPT_EXPERT, { ©_unknown_streams },"Copy unknown stream types" },{ "c", HAS_ARG | OPT_STRING | OPT_SPEC |OPT_INPUT | OPT_OUTPUT, { .off &＃61; OFFSET(codec_names) },"codec name", "codec" },{ "codec", HAS_ARG | OPT_STRING | OPT_SPEC |OPT_INPUT | OPT_OUTPUT, { .off &＃61; OFFSET(codec_names) },"codec name", "codec" },{ "pre", HAS_ARG | OPT_STRING | OPT_SPEC |OPT_OUTPUT, { .off &＃61; OFFSET(presets) },"preset name", "preset" },

typedef struct OptionDef {const char *name;int flags;
#define HAS_ARG 0x0001
#define OPT_BOOL 0x0002
#define OPT_EXPERT 0x0004
#define OPT_STRING 0x0008
#define OPT_VIDEO 0x0010
#define OPT_AUDIO 0x0020
#define OPT_INT 0x0080
#define OPT_FLOAT 0x0100
#define OPT_SUBTITLE 0x0200
#define OPT_INT64 0x0400
#define OPT_EXIT 0x0800
#define OPT_DATA 0x1000
#define OPT_PERFILE 0x2000 /* the option is per-file (currently ffmpeg-only).implied by OPT_OFFSET or OPT_SPEC */
#define OPT_OFFSET 0x4000 /* option is specified as an offset in a passed optctx */
#define OPT_SPEC 0x8000 /* option is to be stored in an array of SpecifierOpt.Implies OPT_OFFSET. Next element after the offset isan int containing element count in the array. */
#define OPT_TIME 0x10000
#define OPT_DOUBLE 0x20000
#define OPT_INPUT 0x40000
#define OPT_OUTPUT 0x80000union {void *dst_ptr;int (*func_arg)(void *, const char *, const char *);size_t off;} u;const char *help;const char *argname;
} OptionDef;

groups参数为输入输出参数

static const OptionGroupDef groups[] &＃61; {[GROUP_OUTFILE] &＃61; { "output url", NULL, OPT_OUTPUT },[GROUP_INFILE] &＃61; { "input url", "i", OPT_INPUT },
};

typedef struct OptionGroupDef {/**} OptionGroupDef;

通过代码来分析split_commandline()函数的执行过程&＃xff1a;

/*** 解析命令行参数* &＃64;param octx: 用来将命令行中的参数通过分析分别存入此结构对应变量中* &＃64;param options: 默认参数的定义 (具体参见ffmpeg_opt.c文件中的 const OptionDef options[] 定义)* &＃64;param groups: 存储输入文件和输出文件相关参数* &＃64;param nb_groups: 2*/
int split_commandline(OptionParseContext *octx, int argc, char *argv[],const OptionDef *options,const OptionGroupDef *groups, int nb_groups)
{int optindex &＃61; 1;int dashdash &＃61; -2;/* perform system-dependent conversions for arguments list */prepare_app_arguments(&argc, &argv);/* 基本的内存分配&＃xff0c;OptionGroupDef 与 OptionParseContext 建立联系 */init_parse_context(octx, groups, nb_groups, data);av_log(NULL, AV_LOG_DEBUG, "Splitting the commandline.\n");/* 循环取出参数 */while (optindex cur_group数组的值以及专属参数&＃xff0c;存储到 * octx->groups[0]结构体中,并清空 octx->cur_group 数组的值*/finish_group(octx, 0, opt);av_log(NULL, AV_LOG_DEBUG, " matched as %s.\n", groups[0].name);continue;}/* 排除以 -- 开头 & 输出文件定义&＃xff0c;剩下的就是标准参数形式将参数的类型指针 &＃43;1&＃xff0c;把 - 去掉 */opt&＃43;&＃43;;#define GET_ARG(arg) \
do { \arg &＃61; argv[optindex&＃43;&＃43;]; \if (!arg) { \av_log(NULL, AV_LOG_ERROR, "Missing argument for option &＃39;%s&＃39;.\n", opt);\return AVERROR(EINVAL); \} \
} while (0)/* 参数格式是否为“-i xxx”&＃xff0c;如果匹配&＃xff0c;返回1 */if ((ret &＃61; match_group_separator(groups, nb_groups, opt)) >&＃61; 0) {// 获取参数对应的值GET_ARG(arg);/** * 将输入的路径、octx->cur_group数组的值以及专属参数&＃xff0c;存储到 * octx->groups[0]结构体中,并清空 octx->cur_group 数组的值*/finish_group(octx, ret, arg);av_log(NULL, AV_LOG_DEBUG, " matched as %s with argument &＃39;%s&＃39;.\n",groups[ret].name, arg);continue;}// 判断此 opt 是否为 options 中定义的参数po &＃61; find_option(options, opt);if (po->name) {if (po->flags & OPT_EXIT) {arg &＃61; argv[optindex&＃43;&＃43;];} else if (po->flags & HAS_ARG) {/* 获取参数 */GET_ARG(arg);} else {// 允许参数后面的值缺失&＃xff0c;直接设置为1arg &＃61; "1";}/*** 判断参数类型(opt->flags)&＃xff0c;存入 octx->global_opts(全局参数) 或 * octx->cur_group(临时数组)*/add_opt(octx, po, opt, arg);av_log(NULL, AV_LOG_DEBUG, " matched as option &＃39;%s&＃39; (%s) with ""argument &＃39;%s&＃39;.\n", po->name, po->help, arg);continue;}if (argv[optindex]) {/*** 在 avcodec_options、avformat_options、avresample_options、 * swscale_options、swresample 中的 options 参数中不断查找&＃xff0c;查找专属 * 并存入 AVDictionary*/ret &＃61; opt_default(NULL, opt, argv[optindex]);if (ret >&＃61; 0) {av_log(NULL, AV_LOG_DEBUG, " matched as AVOption &＃39;%s&＃39; with ""argument &＃39;%s&＃39;.\n", opt, argv[optindex]);optindex&＃43;&＃43;;continue;} else if (ret !&＃61; AVERROR_OPTION_NOT_FOUND) {// 参数格式错误av_log(NULL, AV_LOG_ERROR, "Error parsing option &＃39;%s&＃39; ""with argument &＃39;%s&＃39;.\n", opt, argv[optindex]);return ret;}}/* 处理 “-noxx" 格式参数 */if (opt[0] &＃61;&＃61; &＃39;n&＃39; && opt[1] &＃61;&＃61; &＃39;o&＃39; &&(po &＃61; find_option(options, opt &＃43; 2)) &&po->name && po->flags & OPT_BOOL) {// 存入默认值 ”0“add_opt(octx, po, opt, "0");av_log(NULL, AV_LOG_DEBUG, " matched as option &＃39;%s&＃39; (%s) with ""argument 0.\n", po->name, po->help);continue;}// 没有匹配的参数&＃xff0c;返回错误av_log(NULL, AV_LOG_ERROR, "Unrecognized option &＃39;%s&＃39;.\n", opt);return AVERROR_OPTION_NOT_FOUND;}// 循环结束后&＃xff0c;临时参数及专属参数还存在值&＃xff0c;没有存储到输入&输出相关参数数组中if (octx->cur_group.nb_opts || codec_opts || format_opts || resample_opts)av_log(NULL, AV_LOG_WARNING, "Trailing options were found on the ""commandline.\n");av_log(NULL, AV_LOG_DEBUG, "Finished splitting the commandline.\n");return 0;
}


总结&＃xff1a;跳过“--”开头的参数&＃xff0c;分别解析“-”、“-no”、“-i”开头的参数以及输出参数&＃xff0c;存入OptionParseContext *octx中。