npm package: @oltodo/subsrt
Description: Subtitle converter
Author: Papn Kukn
Latest version: 1.0.0

# subsrt

Subtitle converter JavaScript library and command line tool.

## Getting Started

Install the module
```
npm install -g subsrt
```

Command line
```
subsrt --help
subsrt convert sample.sub sample.srt
```

Using as Node.js library
```javascript
var subsrt = require('subsrt');

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

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

## Supported subtitle formats

* [MicroDVD SUB](https://en.wikipedia.org/wiki/MicroDVD) (.sub)
* [SubRip](https://en.wikipedia.org/wiki/SubRip) (.srt)
* [SubViewer](https://en.wikipedia.org/wiki/SubViewer) (.sbv)
* [WebVTT](https://w3c.github.io/webvtt/) (.vtt)
* [SubStation Alpha](https://en.wikipedia.org/wiki/SubStation_Alpha) (.ssa and .ass)
* [SAMI](https://en.wikipedia.org/wiki/SAMI) (.smi) aka Synchronized Accessible Media Interchange
* [LRC](https://en.wikipedia.org/wiki/LRC_%28file_format%29) (.lrc) aka LyRiCs
* JSON (.json)

## 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
```

## 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 duration or changing FPS.

### List supported formats

```javascript
var subsrt = require('subsrt');
var 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
```javascript
var subsrt = require('subsrt');
var handler = subsrt.format['srt'];
//handler = { name: 'srt', helper: [object], parse: [function], build: [function] }
```

To implement a new subtitle format handler do the following
```javascript
var subsrt = require('subsrt');
subsrt.format['my'] = { //'my' is the format name
  name: 'my',
  parse: function(content, options) {
    var captions = [ ];
    //...
    return captions;
  },
  build: function(captions, options) {
    var content = "";
    //...
    return content;
  },
  detect: function(captions, options) {
    if (content.indexOf("my") > 0) {
      return true; //Recognized
    }
  }
};
```

### Detect

Recognizes format by content
```javascript
var subsrt = require('subsrt');

var 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';

var format = subsrt.detect(content);
//format = 'srt'
```

### Parse

Parse a subtitle file
```javascript
var fs = require('fs');
var subsrt = require('subsrt');

//Read a .srt file
var content = fs.readFileSync('sample.srt', 'utf8');

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

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

Example of output
```javascript
[
  {
    "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 seconds, `sub` format only
* `preserveSpaces`: keep white space lines, `smi` format only

### Build

Build a subtitle file
```javascript
var fs = require('fs');
var subsrt = require('subsrt');

//Sample captions
var 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
var options = { format: 'vtt' };
var content = subsrt.build(captions, options);

//Write content to .vtt file
fs.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 seconds, `sub` format only
* `closeTags`: set to true to close tags, `smi` format only

### Convert

Using a single action to convert from one to another subtitle format
```javascript
var fs = require('fs');
var subsrt = require('subsrt');

//Read a .srt file
var srt = fs.readFileSync('sample.srt', 'utf8');

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

//Write content to .sbv file
fs.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 seconds, `sub` format only
* `resync`: resync options, see below

### Time shift (+/- offset)

Example to make an extra 3 second delay
```javascript
var fs = require('fs');
var subsrt = require('subsrt');

//Read a .srt file
var content = fs.readFileSync('sample.srt', 'utf8');
var captions = subsrt.parse(content);

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

Use minus sign to display captions earlier
```javascript
var resynced = subsrt.resync(captions, { offset: -3000 });
```

### Change FPS

The .sub format has captions saved in frame unit. To shift from 25 FPS to 30 FPS do the following
```javascript
var fs = require('fs');
var subsrt = require('subsrt');

//Read a .sub file
var content = fs.readFileSync('sample.sub', 'utf8');
var 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
var resynced = subsrt.resync(content, { ratio: 30 / 25, frame: true });
```

### Advanced resync options

Extend caption duration by 500 ms
```javascript
var resynced = subsrt.resync(content, function(a) {
  //Argument 'a' is an array with two elements: [ start, end ]
  return [ a[0], a[1] + 500 ]; //Return shifted [ start, end ] values
});
```

## Source Code

Download the source code from GitHub repository.

Install required packages if any
```
npm install
```

Run the unit tests
```
npm test
```

Optionally create a folder `output` in the `test` folder before running the tests.
This will allow you to view the generated contents.