change vtt format to srt format in order to be loaded by player

change_vtt_to_srt.cc

#include <iostream>
#include <string>
#include <fstream>
#include <thread>
#include <regex>
#include <cstdio>

using namespace std;

int main(int argc,char* argv[])
{
        if (argc < 2) {
                printf("filename not given\n");
                exit(-1);
        }
        int i = 1;
        while (i < argc) {
                string filename(argv[i++]);
                string line;
                ifstream in(filename);

                //把文件后缀.vtt换成.srt,
                regex name_pattern("(.*\\.)vtt");
                //regex name_pattern("(.*\\.)en.vtt");
                string replace = "$1srt";
                string newname = regex_replace(filename,name_pattern,replace);

                ofstream fout(newname);

                regex ecma_pattern("(\\d{2}):(\\d{2}).*");
                //regex basic_pattern("[0-9]\\{2\\}:[0-9]\\{2\\}.*",regex::basic);

                //用来把点号换成逗号
                regex replace_period("(\\d{2}:\\d{2}:\\d{2})\\.(\\d{3} --> )(\\d{2}:\\d{2}:\\d{2})\\.");
                string replace2 = "$1,$2$3,";

                int cnt = 1;
                int ignore = 0;
                while (std::getline(in,line)) {
                        /*
                           前三行是这三行，忽略
                                WEBVTT
                                Kind: captions
                                Language: en
                        */
                        if (ignore++ < 3) continue;

                        if (regex_match(line,ecma_pattern)) {
                                fout << cnt++ << endl;
                                fout << regex_replace(line,replace_period,replace2) << endl;
                                continue;
                        }
                        fout << line << endl;
                }

                in.close();
                fout.close();
                //std::remove(filename.c_str());//也许手工删除vtt文件要好
        }
        return 0;
}

ffmpeg -i vtt srt