CaptionStack
Private by design

JSON CONVERTER

JSON files.
Any format.

Convert .json captions to SRT, VTT, TTML, and more — or convert anything to .json. Free, private, and in your browser.

SRTVTTSBVLRCTTMLJSONCSVTXT
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.

About JSON (.json) files

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.

Where .json is used

  • Custom web players and apps
  • Transcription and speech-to-text APIs
  • Data analysis and search indexing

What a .json file looks like

{
  "version": 1,
  "cues": [
    { "id": "1", "start": 1000, "end": 4200, "text": "Caption files, meet your new converter." }
  ]
}

What converts and what doesn’t

Lossless for timing, text, and identifiers. Timestamps are exported as integer milliseconds.

Convert JSON to…

Convert to JSON from…

All caption formats