dsc-uob/subtitle

Subtitle

A library that makes it easy to work with multiple subtitle/caption file formats, written with highly efficient code, highly customizable (90%), supports Sound Null Safety.

Currently supported formats:

• WebVTT (including named cue identifiers and positioning directives)
• SRT (SubRip)
• TTML (Timed Text Markup Language)
• DFXP (Distribution Format Exchange Profile)
• Custom Subtitle Format

Highlights

• Line-based VTT/SRT parser — no backtracking; handles large karaoke-style files in milliseconds.
• O(log n + k) multi-cue search via binary upper-bound + prefix-max-end array.
• Automatic cue deduplication — collapses same-range duplicates and merges identical adjacent cues.
• Encoding fallback — tries UTF-8, falls back to Latin-1 for legacy subtitle files.

Created by Muhammad Hasan Alasady under a MIT LICENSE.

Usage

You have a lot of way to use this package, with internet, local file, assets file(In flutter), and from string. In this section you will learn how to use each of this:

1. Internet Subtitles

You have two ways to use subtitles on the internet, firstly using SubtitleController and it's the easly way, secondly by using SubtitleProvider and SubtitleParser, this is both of ways:

• By SubtitleController:

Firstly provide the link of subtitle (should be an object of Uri), after that you can use SubtitleProvider.fromNetwork(url) or NetworkSubtitle(url):

var url = Uri.parse(
    'https://brenopolanski.github.io/html5-video-webvtt-example/MIB2-subtitles-pt-BR.vtt');
var controller = SubtitleController(
  provider: SubtitleProvider.fromNetwork(url),
);

Or

var url = Uri.parse(
    'https://brenopolanski.github.io/html5-video-webvtt-example/MIB2-subtitles-pt-BR.vtt');
var controller = SubtitleController(
  provider: NetworkSubtitle(url),
);

• By SubtitleProvider and SubtitleParser:

Like the last one, provide the link and provider, after that create a new object of SubtitleObject and await it to preparing the subtitle data, in the last you can use SubtitleParser to parsing the subtitles:

var url = Uri.parse(
    'https://brenopolanski.github.io/html5-video-webvtt-example/MIB2-subtitles-pt-BR.vtt');

SubtitleProvider provider = NetworkSubtitle(url);
SubtitleObject object = await provider.getSubtitle();
SubtitleParser parser = SubtitleParser(object);     

After creating the controller you have to initialize it by call controller.initial(), it's async function, so you have to await it.

await controller.initial();

When you intialize it, you can use this methods to dealing with subtitles:

1. controller.subtitles: The List of subtitles.
2. controller.durationSearch(<Your Duration>): Provide a duration to fetch the first subtitle in range of this duration.
3. controller.multiDurationSearch(<Your Duration>): Provide a duration to fetch a list of subtitles in range of this duration.
4. controller.getAll(<separator optional>): Return all subtitles as a single string with custom separator (default is ', ').

Check the API Reference or GitHub Wiki for more

2. File Subtitles

Like the last one, you have same two ways, just prepare your file, and replace the SubtitleProvider in all places to be SubtitleProvider.fromFile(file) or FileSubtitle(file)

• By SubtitleController:

var file = File('example/data.vtt');
var controller = SubtitleController(
  provider: SubtitleProvider.fromNetwork(file),
);

Or

var file = File('example/data.vtt');
var controller = SubtitleController(
  provider: FileSubtitle(file),
);

• By SubtitleProvider and SubtitleParser:

var file = File('example/data.vtt');

SubtitleProvider provider = FileSubtitle(file);
SubtitleObject object = await provider.getSubtitle();
SubtitleParser parser = SubtitleParser(object);

3. String Subtitles

Same others just replace providers to be instance of StringSubtitle or SubtitleProvider.fromString().

4. Flutter Asset

In flutter asset case you have to create you class (called it like AssetSubtitle), by extends SubtitleProvider, and use rootBundle to load the string of asset file, after created it, do like first example, just replace providers to be instance of your new class, like:

class AssetSubtitle extends SubtitleProvider {
  /// The subtitle path in your assets.
  final String path;
  final SubtitleType? type;

  const AssetSubtitle(
    this.path, {
    this.type,
  });

  @override
  Future<SubtitleObject> getSubtitle() async {
    // Preparing subtitle file data by reading the file.
    final data = await rootBundle.loadString(path);

    // Find the current format type of subtitle.
    final ext = extension(path);
    final type = this.type ?? getSubtitleType(ext);

    return SubtitleObject(data: data, type: type);
  }
}

When you need to use it:

var path = 'files/subtitles/1.vtt';
var controller = SubtitleController(
  provider: AssetSubtitle(path),
);

Components

• SubtitleProvider: Simplifies fetching subtitle file data from multiple sources.
• SubtitleRepository: Deals with the platform directly to get or download the required data and submit it to the provider.
• SubtitleParser: Used to analyze and convert subtitle files into software objects that are viewable and usable.
• CustomSubtitleParser: Customizable subtitle parser, for custom regexes.
• SubtitleRegexObject: Responsible for providing the necessary expression for the purpose of decoding the content of subtitle files, has 4 children:
  • VttRegex: WebVTT regexp.
  • SrtRegex: SubRip regexp.
  • TtmlRegex: TTML or DFXP regex
  • CustomRegex: User define regexp.
• SubtitleObject: Store the subtitle file data and its format type.
• SubtitleController: Controller subtitles, preparing it, decoding, sorting, and search.

Example

import 'package:subtitle/subtitle.dart';

const vttData = '''WEBVTT FILE

5
00:00:19.000 --> 00:00:24.000
Which is why we are bringing TV, internet and phone together in <c.highlight>one</c> super package

3
00:00:11.000 --> 00:00:14.000 A:end
Phone conversations where people truly <c.highlight>connect</c>

1
00:00:03.500 --> 00:00:05.000 D:vertical A:start
Everyone wants the most from life

2
00:00:06.000 --> 00:00:09.000 A:start
Like internet experiences that are rich <b>and</b> entertaining


4
00:00:14.500 --> 00:00:18.000
Your favourite TV programmes ready to watch at the touch of a button

6
00:00:24.500 --> 00:00:26.000
<c.highlight>One</c> simple way to get everything

7
00:00:26.500 --> 00:00:27.500 L:12%
UPC

8
00:00:28.000 --> 00:00:30.000 L:75%
Simply for <u>everyone</u>''';

void main(List<String> args) async {
  //! By using controller
  var controller = SubtitleController(
      provider: SubtitleProvider.fromString(
    data: vttData,
    type: SubtitleType.vtt,
  ));

  await controller.initial();
  printResult(controller.subtitles);

  //! By using objects
  var object = SubtitleObject(
    data: vttData,
    type: SubtitleType.vtt,
  );
  var parser = SubtitleParser(object);
  printResult(parser.parsing());
}

void printResult(List<Subtitle> subtitles) {
  subtitles.sort((s1, s2) => s1.compareTo(s2));
  for (var result in subtitles) {
    print(
        '(${result.index}) Start: ${result.start}, end: ${result.end} [${result.data}]');
  }
}