rakuzen25/subsrt-ts

Subtitle JavaScript library and command line tool with no dependencies.

subsrt-ts

Docs · npm package

Subtitle JavaScript library and command line tool with no dependencies.

This is a rewrite of the original subsrt package in TypeScript and using ESM syntax.

Table of Contents

1. Getting started
2. Supported subtitle formats
3. Command line arguments
4. Using in JavaScript
   • List supported formats
   • Detect
   • Parse
   • Build
   • Convert
   • Timeshift (+/- offset)
   • Change FPS
   • Advanced resync options
5. Source code
6. License

Getting started

Install the module

npm install -g subsrt

Command line

subsrt --help
subsrt convert sample.sub sample.srt

Using as Node.js library

import subsrt from "subsrt";

// MicroDVD (.sub) content
const sub = "{14975}{104000}Hi, my name is...";

// Convert to SubRip (.srt) content
const srt = subsrt.convert(sub, { format: "srt", fps: 25 });

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Supported subtitle formats

• MicroDVD SUB (.sub)
• SubRip (.srt)
• SubViewer (.sbv)
• WebVTT (.vtt)
• SubStation Alpha (.ssa and .ass)
• SAMI (.smi) aka Synchronized Accessible Media Interchange
• LRC (.lrc) aka LyRiCs
• JSON (.json)

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Command line arguments

Usage:
  subsrt [command] [options]

Commands:
  list                   List supported formats
  parse [src] [json]     Parse a subtitle file
  build [json] [dst]     Create a subtitle file from captions
  detect [src]           Detect subtitle file format, if supported
  resync [src] [dst]     Resync FPS or shift time (+/- offset)
  convert [src] [dst]    Converts a subtitle format

Options:
  --help                 Print this message
  --eol [chars]          End of line chars, e.g. \r\n
  --fps [fps]            Frames per second for .sub format
  --offset [time]        Resync time shift offset in ms
  --format [ext]         Subtitle format to convert/build/parse
  --verbose              Enable detailed logging
  --version              Print version number

Examples:
  subsrt parse sample.sbv
  subsrt parse sample.srt output.json
  subsrt parse sample.sub --fps 30
  subsrt build input.json output.vtt
  subsrt build input.json --format sbv
  subsrt detect unknown.txt
  subsrt convert sample.srt sample.vtt
  subsrt convert --offset -250 sample.srt sample.ssa
  subsrt resync --offset +3000 input.srt output.srt
  subsrt resync --fps 25-30 input.sub output.sub

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Using in JavaScript

The Node.js library supports converting, parsing and building subtitle file formats. Subtitles can also be resynced by shifting time offset, extending the duration or changing FPS.

List supported formats

import subsrt from "subsrt";

const list = subsrt.list();

console.log(list.join(", "));
// vtt, lrc, smi, ssa, ass, sub, srt, sbv, json

Format name is used in conversion options, e.g. { format: "srt" }

Use subsrt.format.name to access functions directly

import subsrt from "subsrt";
const handler = subsrt.format.srt;
// handler = { name: 'srt', helper: [object], parse: [function], build: [function] }

To implement a new subtitle format handler do the following

import subsrt from "subsrt";
subsrt.format.my = {
    // "my" is the format name
    name: "my",
    parse: (content, options) => {
        const captions = [];
        // ...
        return captions;
    },
    build: (captions, options) => {
        const content = "";
        // ...
        return content;
    },
    detect: (content) => {
        if (content.indexOf("my") > 0) {
            return true; // Recognized
        }
    },
};

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Detect

Recognizes format by content

import subsrt from "subsrt";

let content = "";
content += "5" + "\r\n";
content += "00:00:16,700 --> 00:00:21,480" + "\r\n";
content += "Okay, so we have all the ingredients laid out here" + "\r\n";

const format = subsrt.detect(content);
// format = "srt"

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Parse

Parse a subtitle file

import { readFileSync } from "fs";

import subsrt from "subsrt";

// Read a .srt file
const content = readFileSync("sample.srt", "utf8");

// Parse the content
const options = { verbose: true };
const captions = subsrt.parse(content, options);

// Output to console
console.log(captions);

Example of output

[
    {
        "type": "caption", // "caption" or "meta"
        "index": 1, // Caption id, usually a sequential number
        "start": 599, // Time to show caption in milliseconds
        "end": 4160, // Time to hide caption in milliseconds
        "duration": 3561, // Calculated caption duration
        "content": ">> ALICE: Hi, my name is Alice Miller and this is John Brown", // Formatted content
        "text": "Hi, my name is Alice Miller and this is John Brown" // Plain text content
    },
    {
        "type": "caption",
        "index": 2,
        "start": 4160,
        "end": 6770,
        "duration": 2610,
        "content": ">> JOHN: and we're the owners of Miller Bakery.",
        "text": "and we're the owners of Miller Bakery."
    }
    // ...
]

List of options

• format: explicitly select a parser, values: sub, srt, sbv, vtt, lrc, smi, ssa, ass, json, default is undefined to auto detect
• verbose: set to true for extra messages, console only, default: false
• eol: end of line character(s), default: \r\n
• fps: frames per second, sub format only
• preserveSpaces: keep white space lines, smi format only

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Build

Build a subtitle file

import { writeFileSync } from "fs";

import subsrt from "subsrt";

// Sample captions
const captions = [
    {
        start: 599, // Time to show caption in milliseconds
        end: 4160, // Time to hide caption in milliseconds
        text: "Hi, my name is Alice Miller and this is John Brown", // Plain text content
    },
    {
        start: 4160,
        end: 6770,
        text: "and we're the owners of Miller Bakery.",
    },
];

// Build the WebVTT content
const options = { format: "vtt" };
const content = subsrt.build(captions, options);

// Write content to .vtt file
writeFileSync("generated.vtt", content);

List of options

• format: required, output subtitle format, values: sub, srt, sbv, vtt, lrc, smi, ssa, ass, json, default: srt
• verbose: set to true for extra messages, console only, default: false
• fps: frames per second, sub format only
• closeTags: set to true to close tags, smi format only

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Convert

Using a single action to convert from one to another subtitle format

import { readFileSync, writeFileSync } from "fs";

import subsrt from "subsrt";

// Read a .srt file
const srt = readFileSync("sample.srt", "utf8");

// Convert .srt to .sbv
const sbv = subsrt.convert(srt, { format: "sbv" });

// Write content to .sbv file
writeFileSync("converted.sbv", sbv);

List of options

• format: required, output subtitle format, values: sub, srt, sbv, vtt, lrc, smi, ssa, ass, json, default: srt
• verbose: set to true for extra messages, console only, default: false
• eol: end of line character(s), default: \r\n
• fps: frames per second, sub format only
• resync: resync options, see below

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Timeshift (+/- offset)

An example to make an extra 3-second delay

import { readFileSync } from "fs";

import subsrt from "subsrt";

// Read a .srt file
const content = readFileSync("sample.srt", "utf8");
const captions = subsrt.parse(content);

// Returns updated captions
const resynced = subsrt.resync(captions, { offset: 3000 });

Use minus sign to display captions earlier

const resynced = subsrt.resync(captions, { offset: -3000 });

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Change FPS

The .sub format has captions saved in frame units. To shift from 25 FPS to 30 FPS do the following

import { readFileSync } from "fs";

import subsrt from "subsrt";

// Read a .sub file
const content = readFileSync("sample.sub", "utf8");
const captions = subsrt.parse(content, { fps: 25 }); // The .sub file content is saved in 25 FPS units

// Convert to 30 FPS, make sure to set 'frame' to true to convert frames instead of time
const resynced = subsrt.resync(content, { ratio: 30 / 25, frame: true });

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Advanced resync options

Extend caption duration by 500 ms

// Argument 'a' is an array with two elements: [ start, end ]
// Return shifted [ start, end ] values
const resynced = subsrt.resync(content, (a) => [a[0], a[1] + 500]);

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Source code

Download the source code from the GitHub repository.

Install required packages if any

pnpm install

Run the unit tests

pnpm test

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License

Distributed under the MIT License. See LICENSE.txt for more information.

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