CaptionStack
Private by design

JSON TO TTML

JSON to TTML.

Convert JSON (.json) subtitles to TTML (.ttml) in seconds. No upload, no sign-up, nothing leaves your browser.

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1

Choose your caption file

We’ll detect the format automatically. Drop several files to convert them all at once.

Don’t have a file handy?
2

Choose an output format

Select what you need on the other side.

100% privateYour files never leave this device.
8 formatsBuilt for the caption formats you use.
No limitsConvert as often as you need.

How to convert JSON to TTML

  1. Drop your .json file into the converter above, or click to browse. Several files at once become a ZIP.
  2. Check the quality report and fix timing or text in the editor if you need to.
  3. TTML is already selected as the output format. Click Download converted file.

Conversion happens entirely in your browser. Nothing is uploaded, no account is needed, and there is no file count limit.

About JSON (.json)

JSON is the easiest format to consume from code. CaptionStack reads an array of cue objects or an object with a cues array, accepts timestamps as milliseconds or time strings, and writes a versioned document with millisecond start and end values so you can load captions straight into a web app, database, or analytics pipeline.

About TTML (.ttml)

Timed Text Markup Language is a W3C XML format for captions and subtitles. It underpins broadcast standards such as EBU-TT and IMSC and is required by many streaming platforms and accessibility regulations. Each <p> element carries begin and end (or dur) attributes and the caption text.

What changes when converting JSON to TTML

Text, timing, and xml:id identifiers are converted. Styles, regions, and layout metadata are not preserved, and inline <span> formatting is flattened to plain text with <br/> becoming line breaks.

Frequently asked questions

Is this JSON to TTML converter free?
Yes. CaptionStack is free and open source, with no limits on file count or conversions.
Are my caption files uploaded anywhere?
No. Parsing and conversion run in your browser using a local Web Worker. Your files never leave your device.
Can I edit the captions before exporting to TTML?
Yes. After import, open the editor to adjust start and end times, fix text, split, merge, or reorder cues. The quality report flags overlaps, short cues, and fast reading speeds with one-click fixes.
Can I convert many .json files to .ttml at once?
Yes. Drop multiple files and download all of the results as a single ZIP archive.

Other JSON conversions

Other ways to get TTML

All caption formats