ffmepg源码中的 -re

原来ffmpeg中的参数对应是这样的

#define OFFSET(x) offsetof(OptionsContext, x)
const OptionDef options[] = {
    /* main options */
#include "cmdutils_common_opts.h"
    { "f",              HAS_ARG | OPT_STRING | OPT_OFFSET |
                        OPT_INPUT | OPT_OUTPUT,                      { .off       = 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,                       {              &copy_unknown_streams },
        "Copy unknown stream types" },
    { "c",              HAS_ARG | OPT_STRING | OPT_SPEC |
                        OPT_INPUT | OPT_OUTPUT,                      { .off       = OFFSET(codec_names) },
        "codec name", "codec" },
    { "codec",          HAS_ARG | OPT_STRING | OPT_SPEC |
                        OPT_INPUT | OPT_OUTPUT,                      { .off       = OFFSET(codec_names) },
        "codec name", "codec" },
    { "pre",            HAS_ARG | OPT_STRING | OPT_SPEC |
                        OPT_OUTPUT,                                  { .off       = OFFSET(presets) },
        "preset name", "preset" },
    { "map",            HAS_ARG | OPT_EXPERT | OPT_PERFILE |
                        OPT_OUTPUT,                                  { .func_arg = opt_map },
        "set input stream mapping",
        "[-]input_file_id[:stream_specifier][,sync_file_id[:stream_specifier]]" },
    { "map_channel",    HAS_ARG | OPT_EXPERT | OPT_PERFILE | OPT_OUTPUT, { .func_arg = opt_map_channel },
        "map an audio channel from one stream to another", "file.stream.channel[:syncfile.syncstream]" },
    { "map_metadata",   HAS_ARG | OPT_STRING | OPT_SPEC |
                        OPT_OUTPUT,                                  { .off       = OFFSET(metadata_map) },
        "set metadata information of outfile from infile",
        "outfile[,metadata]:infile[,metadata]" },
    { "map_chapters",   HAS_ARG | OPT_INT | OPT_EXPERT | OPT_OFFSET |
                        OPT_OUTPUT,                                  { .off = OFFSET(chapters_input_file) },
        "set chapters mapping", "input_file_index" },
    { "t",              HAS_ARG | OPT_TIME | OPT_OFFSET |
                        OPT_INPUT | OPT_OUTPUT,                      { .off = OFFSET(recording_time) },
        "record or transcode \"duration\" seconds of audio/video",
        "duration" },
    { "to",             HAS_ARG | OPT_TIME | OPT_OFFSET | OPT_OUTPUT,  { .off = OFFSET(stop_time) },
        "record or transcode stop time", "time_stop" },
    { "fs",             HAS_ARG | OPT_INT64 | OPT_OFFSET | OPT_OUTPUT, { .off = OFFSET(limit_filesize) },
        "set the limit file size in bytes", "limit_size" },
    { "ss",             HAS_ARG | OPT_TIME | OPT_OFFSET |
                        OPT_INPUT | OPT_OUTPUT,                      { .off = OFFSET(start_time) },
        "set the start time offset", "time_off" },
    { "sseof",          HAS_ARG | OPT_TIME | OPT_OFFSET |
                        OPT_INPUT | OPT_OUTPUT,                      { .off = OFFSET(start_time_eof) },
        "set the start time offset relative to EOF", "time_off" },
    { "seek_timestamp", HAS_ARG | OPT_INT | OPT_OFFSET |
                        OPT_INPUT,                                   { .off = OFFSET(seek_timestamp) },
        "enable/disable seeking by timestamp with -ss" },
    { "accurate_seek",  OPT_BOOL | OPT_OFFSET | OPT_EXPERT |
                        OPT_INPUT,                                   { .off = OFFSET(accurate_seek) },
        "enable/disable accurate seeking with -ss" },
    { "itsoffset",      HAS_ARG | OPT_TIME | OPT_OFFSET |
                        OPT_EXPERT | OPT_INPUT,                      { .off = OFFSET(input_ts_offset) },
        "set the input ts offset", "time_off" },
    { "itsscale",       HAS_ARG | OPT_DOUBLE | OPT_SPEC |
                        OPT_EXPERT | OPT_INPUT,                      { .off = OFFSET(ts_scale) },
        "set the input ts scale", "scale" },
    { "timestamp",      HAS_ARG | OPT_PERFILE | OPT_OUTPUT,          { .func_arg = opt_recording_timestamp },
        "set the recording timestamp ('now' to set the current time)", "time" },
    { "metadata",       HAS_ARG | OPT_STRING | OPT_SPEC | OPT_OUTPUT, { .off = OFFSET(metadata) },
        "add metadata", "string=string" },
    { "program",        HAS_ARG | OPT_STRING | OPT_SPEC | OPT_OUTPUT, { .off = OFFSET(program) },
        "add program with specified streams", "title=string:st=number..." },
    { "dframes",        HAS_ARG | OPT_PERFILE | OPT_EXPERT |
                        OPT_OUTPUT,                                  { .func_arg = opt_data_frames },
        "set the number of data frames to output", "number" },
    { "benchmark",      OPT_BOOL | OPT_EXPERT,                       { &do_benchmark },
        "add timings for benchmarking" },
    { "benchmark_all",  OPT_BOOL | OPT_EXPERT,                       { &do_benchmark_all },
      "add timings for each task" },
    { "progress",       HAS_ARG | OPT_EXPERT,                        { .func_arg = opt_progress },
      "write program-readable progress information", "url" },
    { "stdin",          OPT_BOOL | OPT_EXPERT,                       { &stdin_interaction },
      "enable or disable interaction on standard input" },
    { "timelimit",      HAS_ARG | OPT_EXPERT,                        { .func_arg = opt_timelimit },
        "set max runtime in seconds", "limit" },
    { "dump",           OPT_BOOL | OPT_EXPERT,                       { &do_pkt_dump },
        "dump each input packet" },
    { "hex",            OPT_BOOL | OPT_EXPERT,                       { &do_hex_dump },
        "when dumping packets, also dump the payload" },
   <span style="color:#ff0000;"> { </span><span style="color:#cc33cc;">"re", </span><span style="color:#ff0000;">            OPT_BOOL | OPT_EXPERT | OPT_OFFSET |
                        OPT_INPUT,                                   { .off = OFFSET(</span>rate_emu)<span style="color:#ff0000;"> },      //======说明参数  -re 对应 源码中的参数 rate_emu</span>
        "read input at native frame rate", "" },
    { "target",         HAS_ARG | OPT_PERFILE | OPT_OUTPUT,          { .func_arg = opt_target },
        "specify target file type (\"vcd\", \"svcd\", \"dvd\", \"dv\" or \"dv50\" "
        "with optional prefixes \"pal-\", \"ntsc-\" or \"film-\")", "type" },
    { "vsync",          HAS_ARG | OPT_EXPERT,                        { .func_arg = opt_vsync },
        "video sync method", "" },
    { "frame_drop_threshold", HAS_ARG | OPT_FLOAT | OPT_EXPERT,      { &frame_drop_threshold },
        "frame drop threshold", "" },
    。。。。。
   
};

源码中的相关代码是

---- rate_emu Matches (7 in 3 files) ----
Ffmpeg.c:        if (ifile->rate_emu)
Ffmpeg.c:    if (f->rate_emu) {
Ffmpeg.h:    int rate_emu;
Ffmpeg.h:    int rate_emu;
Ffmpeg_opt.c:    f->rate_emu   = o->rate_emu;
Ffmpeg_opt.c:                        OPT_INPUT,                                   { .off = OFFSET(rate_emu) },

再相应的找对应代码就OK了

主要代码是

static int get_input_packet(InputFile *f, AVPacket *pkt)
{
    if (f->rate_emu) {
        int i;
        for (i = 0; i < f->nb_streams; i++) {
            InputStream *ist = input_streams[f->ist_index + i];
            int64_t pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
            int64_t now = av_gettime_relative() - ist->start;
            if (pts > now)
                return AVERROR(EAGAIN);
        }
    }

#if HAVE_PTHREADS
    if (nb_input_files > 1)
        return get_input_packet_mt(f, pkt);
#endif
    return av_read_frame(f->ctx, pkt);
}

//也就是说控制读取数据来控制的速度