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SubRip Subtitle format (SRT)

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name SubRip Subtitle format (SRT)
Description

SubRip (SRT) is a text-based file format that is created using the free DVD-ripping software SubRip. SubRip allows users to extract subtitles and their timings from DVDs and other video files to a text file, SRT, to be played alongside video or audio (SRT files do not contain the video or audio files). SRT subtitle files are considered the most common subtitle/caption format and most subtitles on the internet follow the SRT format. According to Jean-Marc in Subtitle Formats: What are They and Which Ones to Use?, March 2021, the SRT subtitle format is "The most universal format. It is supported by almost all software, platforms and social networks."

SubRip software:

SubRip's website, zuggy.wz.cz, has a guide for Ripping Subtitle from Video Files Using SubRip, June 2005, that describes how users can extract subtitles. The SubRip software extracts image-based subtitles and their timings. SubRip uses AviSynth, a free video post-production tool and software for editing and processing videos, to extract video frames from a video source. The program then tries to recognize text characters from the images, using semi-automatic text recognition technology (also referred to as Optical Character Recognition (OCR)), for the subtitle ripping process. SubRip settings can be modified to change the detection parameters, but users also can "train" the SubRip program to detect previously filled out characters (duplicates) to be replaced automatically. Once complete, SubRip then stores the converted subtitles in plain text format SRT file.

SubRip SRT files are not encoded in the video, instead the subtitles are displayed on top of the video, with the supporting video/audio media player using the timing information from the SRT files to sync the subtitles or captions properly for viewing.

The SubRip software supports limited text formatting derived from HTML tags, including bold, italic, underline, and color. Rendering of text formatting may be dependent on the video processing application.

The SubRip software can also be used to extract subtitles to be stored as bitmaps for later removal and/or use.

Structure of SRT:

SRT files are basic text files with sequential numbering for each caption, separated by one or more blank lines. The SRT file name should match the name of the video/audio that will be played alongside, example: "MyVideo123.mp4" video file, "MyVideo123.srt" SRT file.

SRT files include four components:

  • Numeric counter indicating the number/position of the subtitle
  • Start/End time of subtitle, separated with --> characters
    • The arrow must consist of two hyphens (--) and a right-pointing angle bracket (>).
    • Timecode format: hours:minutes:seconds,milliseconds (00:00:00,000)
  • Subtitle text, in one or more lines, with a 32-character limit per line
  • Blank line indicating end of subtitle

SRT file content example from SpeechPad.com:

1
00:00:00,498 --> 00:00:02,827
Here's what I love most
about food and diet.
2
00:00:02,827 --> 00:00:06,383
We all eat several times a day,
and we're totally in charge
3
00:00:06,383 --> 00:00:09,427
of what goes on our plate
and what stays off.

See Notes for more information.

Uses of SRT:

According to Rebecca Klein in 3PlayMedia.com's blog article, Caption Format Acronyms, Explained February 2023, "The SubRip (.SRT) file is by far the most common sidecar file for prerecorded web videos, and is preferred by many video hosting platforms (including YouTube) thanks to its adaptability. It can be used for both closed caption and subtitle workflows. .SRTs are also an immensely popular subtitle deliverable because they can contain characters in almost any language and can sometimes be used in video editing software for rendering."

  • Sidecar File: computer file that stores data that is not supported by the source file format.

Gwendolyn DeSilva at HappyScribe.com described SRT in the blog, What is an SRT File? June 2021, as "One of the most frequent types of raw closed caption file formats or subtitle formats is an SRT file, sometimes known as a SubRip (.srt) file."

The use of digital technology and social media has created many changes and uses for subtitles formats, leading to new software tools and methods of delivering subtitles, as well as demand for more high-quality subtitles. Subtitles are useful to viewers for many reasons, including users who are hearing impaired, users who like to supplement subtitles alongside video, and/or users seeking to learn a new language or watch a foreign film.

Indeed.com's Career Development blog, How to Create SRT Subtitles in 8 Steps (Plus Tips), February 2023, lists and describes some reasons why subtitles are an important part of creating effective video presentations, including:

  • Improved accessibility and inclusiveness
  • Increased accuracy
  • More global possibilities
  • Broader audience connections
  • Higher Search Engine Optimization (SEO) potential
  • Reducing Captioning cost
  • Easier editing process
Production phase Although, SRT text files can be created and edited directly in a text-editor, and/or downloaded from third-party vendors, the primary use of a SRT file is as a middle-state format for extracting and storing DVD subtitles/captioning for playback alongside video or audio files.
Relationship to other formats
    May contain HTML, HyperText Markup Language (HTML). SRT files support basic text formatting derived from HTML.
    Has subtype WebVTT, Web Video Text Tracks Format (WebVTT). SRT file format was used as the basis for the WebVTT text track file format. See Notes for more information.

Local use Explanation of format description terms

LC experience or existing holdings Likely exists in LC collections but not separately documented.
LC preference The Library of Congress has not defined format preferences for caption or subtitle files for moving image works in the Recommended Formats Statement.

Sustainability factors Explanation of format description terms

Disclosure

Partial documented. SRT subtitle files are a very simple text format, but not well standardized.

In the Audext.com's Blog post, What is an SRT File and How to Use SRT File for Subtitling?, June 2021, Katrin Deres says "Currently, anyone can create, edit, or download .SRT files as they're an open and free file format that's widely available on the Internet."

Comments welcome.

    Documentation

Little to no information on SRT formal documentation.

Comments welcome.

Adoption

Widely adopted. SRT files are highly compatible with many different video and audio platforms allowing users to create one SRT file to be integrated with variety of platforms including Twitter, Vimeo, and LinkedIn. Use of SRT files continues to increase with digital marketing and improving accessibility of content to audiences.

According to Rev.com, a speech-to-text service company, in their How-to Guide, How to Create & Use SRT Files, October 2020, "As video has grown more popular, it's becoming common practice to add closed captions to support video content wherever its hosted. SRT files are what make it possible to add closed captions or subtitles to video content after it is produced...Using subtitles and captions in this way makes your online content more accessible, allowing a wider audience to interact and engage with your videos."

Comments welcome.

    Licensing and patents

No known license or patent concern for the generation or use of the SRT subtitle format.

Comments welcome.

Transparency

SRT files are human-readable text files that can be edited with any text editor, such as Windows Notepad or Mac TextEdit. SRT files can be created from scratch or downloaded and edited.

Software is available for auto SRT file creation and editing, including Happy Scribe, Zubtitle, and Clideo.

Social media platforms that support video upload, such as Facebook or YouTube, may offer auto captioning support.

SRT subtitle files do not have a character encoding standard, according to the SubRip's Wikipedia page "SubRip's default output encoding is configured as Windows-1252. However, output options are also given for many Windows code pages as well Unicode encodings, such as UTF-8 and UTF-16, with or without byte order mark (BOM)...Which means that any SubRip file parser must attempt to use Charset detection."

Comments welcome.

Self-documentation

SRT files contain a sequence of triplets: start-time, end-time, and text, outside of basic HTML styling (bold, italic, underline, and color) which is dependent on the reader, no inclusion of metadata found. SRT file names should match video/audio file for playback.

Comments welcome.

External dependencies

None beyond availability of supporting software.

Comments welcome.

Technical protection considerations

None.

Comments welcome.


Quality and functionality factors Explanation of format description terms

Text
Normal rendering

SRT files are plain text files consisting of sequenced timestamp blocks with subtitle text, with no character encoding standard.

Comments welcome.

Integrity of document structure

SRT files are plain text files, that follow a particular sequenced structure; a numeric counter indicating number and position of subtitle, start/end times, the subtitle text, followed by a blank line to indicate the end of the subtitle.

Comments welcome.

Integrity of layout and display

SRT file supports some HTML styling, bold, italic, underline, and color, but rendering is dependent on support of the reader.

Comments welcome.

Support for mathematics, formulae, etc.

Little to no information on SRT file's support of mathematics, chemical formulae, diagrams, etc.

Comments welcome.

Functionality beyond normal rendering

None known.

Comments welcome.


File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension srt
See https://www.wikidata.org/wiki/Q105852434.
Internet Media Type text/plain
See https://www.wikidata.org/wiki/Q105852434.
Magic numbers 31 0D 0A 30 30 3A (ASCII: "1↵00:")
See https://en.wikipedia.org/wiki/SubRip.
Other fmt/1218
See http://www.nationalarchives.gov.uk/PRONOM/fmt/1218.
Wikidata Title ID Q105852434
SubRip subtitles (UTF-16). See https://www.wikidata.org/wiki/Q105852434.
Wikidata Title ID Q9332294
SubRip text file format. See https://www.wikidata.org/wiki/Q9332294.

Notes Explanation of format description terms

General

The W3C WebVTT Recommendation acknowledges the SubRip community, stating "Thanks to the SubRip community, including in particular Zuggy and ai4spam, for their work on the SubRip software program whose SRT file format was used as the basis for the WebVTT text track file format."

-

Michał Góral's Subconvert Manual Version 3.0.0 states "Subtitle blocks are separated by an empty line (\n, \r\n or \r, depending on a platform). There is also a second type of SubRip notation available (which is much less frequently met)." The numeric counter can be on the same line as the start/end time, separated by a space.

Example from Subconvert Manual:


0 00:00:00,000 --> 00:00:00,850
This is first subtitle.

1 00:00:01,000 --> 00:00:03,549
This is a simple Sub Rip file
which has more than one line.

History

Limited information on development of software and format. Information search found names V. Zuggy and Brain as developers, but very little more than that.

Zuggy.wz.cz last update November 2018.

Archive site, The Brain's Web (found via Wikipedia) has information about older versions of the software SubRip.


Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: 05/18/2023
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