Subtitles

 I was watching a French movie today and realised that the subtitle was coming up to early - about 1 second too early. It's a bit annoying. So I decided to fix it with a simple Javascript - it runs under Node.js.

//srt_update.js
function main() {
    // syntax: node srt_update.js filename
    // therefore the first argument is the 3rd word in the command line.
    const args = process.argv.slice(2);
    var filename = args[0];
    if (filename == null) {
        console.log("please specify file name.");
        return;
    }
    const readLine = require('readline');
    const f = require('fs');
    var rl = readLine.createInterface({
        input : f.createReadStream(filename),
        output : process.stdout,
        terminal: false
    });
    //const re=/(?<order>\d+)\n(?<start>[\d:,]+)\s+-{2}\>\s+(?<end>[\d:,]+)\n(?<text>[\s\S]*?(?=\n{2}|$))/gi;
    //const re=/(?<start>[\d:,]+)\s+-{2}\>\s+(?<end>[\d:,]+)/gi;
    const re=/(?<shour>[\d]+)[:](?<sminute>[\d]+)[:](?<ssecond>[\d]+)[,](?<smilli>[\d]+)\s+-{2}\>\s+(?<ehour>[\d]+)[:](?<eminute>[\d]+)[:](?<esecond>[\d]+)[,](?<emilli>[\d]+)/gi;
    rl.on('line', function (line) {
        var elements=re.exec(line);
        if (elements!=null) {
            var ssecond = parseInt( elements.groups.ssecond);
            if (ssecond!=59)
                ssecond=String(ssecond+1).padStart(2,'0');
            var esecond = parseInt(elements.groups.esecond);
            if (esecond!=59)
                esecond=String(esecond+1).padStart(2,'0');
            //console.log(`${line} => ${elements.groups.shour}-${elements.groups.sminute}-${ssecond}-${elements.groups.smilli}, ${elements.groups.ehour}-${elements.groups.eminute}-${esecond}-${elements.groups.emilli}`);
            console.log(`${elements.groups.shour}:${elements.groups.sminute}:${ssecond},${elements.groups.smilli} --> ${elements.groups.ehour}:${elements.groups.eminute}:${esecond},${elements.groups.emilli}`);
        } else 
            console.log(line);
    });
}
main();

To run it in a command shell:

$ time node srt_update.js input.srt > output.srt

real    0m1.321s
user    0m0.701s
sys     0m0.062s

An alternative version by not using regular expression:

//srt_update2.js

function main() {

    // syntax: node srt_update.js filename

    // therefore the first argument is the 3rd word in the command line.

    const args = process.argv.slice(2);

    var filename = args[0];

    if (filename == null) {

        console.log("please specify file name.");

        return;

    }

    const readLine = require('readline');

    const f = require('fs');

    var rl = readLine.createInterface({

        input : f.createReadStream(filename),

        output : process.stdout,

        terminal: false

    });

   

    rl.on('line', function (line) {

        var elements = line.split(" --> ", 2);

        if (elements.length==2) {    

            var ssecond=parseInt(elements[0].substring(6, 8));

            var esecond=parseInt(elements[1].substring(6, 8));

            if (ssecond!=59)

                ssecond=String(ssecond+1).padStart(2,'0');

            if (esecond!=59)

                esecond=String(esecond+1).padStart(2,'0');

            console.log(`${elements[0].substring(0,6)}${ssecond}${elements[0].substring(8)} --> ${elements[1].substring(0,6)}${esecond}${elements[1].substring(8)}`);

        } else

            console.log(line);

    });

}

main();

Running result:

$ time node srt_update2.js input.srt > output.srt

real    0m1.304s
user    0m0.701s
sys     0m0.049s

The performance of the two versions seem to be very similar.

Merry Christmas 2021!

 It has been another great year. Merry Christmas and Happy New Year 2022!