This article explains the main characteristics of and differences between SubRip Text (SRT), STL, TTML and DFXP, STL, WebVTT and EBU-TT-D, and what you can use them for.
Choosing the right subtitle format can be a challenge. There are literally hundreds of them, and there is not a single universal standard supported by all subtitle editors and distribution platforms. As a professional using subtitles, you can easily spend hours looking for the right format and for tools to convert between those formats.
Because we know your time is precious and because we want to help you make the best decision, we’ve compiled our recommendations, taking into account the specific use cases. We'll also provide you some tips and tricks.
Characteristics of the Most Common Subtitle File Formats
Selecting the right format is a trade-off between popular and widely adopted, or more functional for the use case you have in mind. However the latter sometimes implies that the format is not generally supported. So in general, the choice of the right format depends on what you plan to do with the subtitles.
The following subtitle formats for import and export are supported with Limecraft:
- SRT (SubRip Text) is perhaps the most basic but for sure the most widely supported of all subtitle formats. SubRip (SubRip Text) files are named with the extension
.srt, and contain formatted lines of plain text in groups separated by a blank line. It is supported by all common distribution platforms.
- STL (EBU Subtitle Data Exchange format) is a legacy standard, widely adopted in the broadcast industry. It was published by the EBU in 1991 and intended to ease the exchange of subtitles between different softwares. It includes the layout and metadata such as the programme title, copyrights, etc. It is a binary format and can't be edited using a text editor.
- TTML (Timed Text Markup Language) and DFXP (Distribution Format eXchange Profile) are closely related standards, both developed by the World Wide Web Consortium (W3C). The work on TTML started in 2003, and it was intended as a super-standard designed to be used for authoring, transcoding or exchanging timed text information including, but not restricted to, subtitling.
- DFXP (Distribution Format eXchange Profile) is the de facto standard for XML captions developed by the World Wide Web Consortium (W3C) in 2005, developed to unify the increasingly divergent set of existing caption formats. It supports the use of colours, positioning, and a variety of other styling characteristics. It became the de facto industry standard, as it was nominate the gold standard by Netflix.
- WebVTT (Web Video Text Track) is a W3C standard for displaying timed text in connection with the HTML5
<track>element. It is based on SRT and the main difference is that WebVTT enables you to edit the color and font of the captioned text. WebVTT is supported by Youtube and Vimeo, but not by Facebook.
- EBU-TT-D (Subtitling Distribution Format) is a modern XML-based format for the distribution of subtitles over IP-based networks. As is the case for DFXP, it is based on W3C Timed Text Markup Language, but adds several extensions. Using EBU-TT-D, you have the best possible control over the styling and the placement, e.g. supporting responsive design (automatically optimising the look and feel for different screen sizes).
The Right Format Depends on the Application
To help you selecting the right format without having to study the different specifications, we advise you to take into consideration the functionality expected by the end user.
- Open (encoded) captions - the practice to irreversibly encode subtitles in the images is deprecated, as you're loosing the ability to display subtitles in other languages. All modern video players (youtube, quicktime,...) today support closed captions, that enable the end-user to switch subtitles on or off. Limecraft supports "burnt-in" captions, and you can as well using 3rd party software like VLC player or Adobe Premiere to permanently encode if that makes sense for your workflow or you require full control over the styling.
- General purpose closed captions - if you have the intention to make available closed captions along the video you make available via various social media, we strongly advise to use SubRip (SRT) format.
- Subtitling for people with a hearing impairment - if you want to use different colours for different speakers, you can export WebVTT for online distribution platforms or STL for broadcast environments.
- Playout in a typical broadcast setup - if you intend to use subtitles in a traditional linear broadcast setup, your safest bet currently is using STL.
- Creating a future proof distribution facility - if you are a broadcaster or VOD service provider and currently looking for setting up a new distribution pipeline, we strongly advise you to consider EBU-TT-D and the pivotal format. It is the most functional and extensible format and likely to become widely supported as well.
Interested to Know More?
Limecraft automated subtitling services use Artificial Intelligence to turn audio into broadcast-grade subtitles using pre-configured subtitling spotting rules, which you can export in several format of choice, including SRT, STL, WebVTT or EBU-TT.
In case you would like to translate existing subtitles in another language for localisation purposes, you can use Limecraft to add one or more languages by uploading your existing media and the existing subtitle file.
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