JSON to VTT
Or paste subtitle text
What this conversion changes
3 things are dropped or need a decision
- Styling
all styling except bold and italic (colour, outline, shadow, margins)
- Positioning
on-screen positioning (every cue returns to the default position)
- Karaoke
karaoke timing (per-syllable highlighting)
This list comes from the capability matrix for these two formats, not from the particular file you loaded. A specific file may lose more if it uses features the format allows but the matrix does not model.
This page converts JSON to VTT. Drop a file in — or paste the text — and you get the VTT version back. The conversion runs entirely in your browser, so nothing is uploaded and no account is needed.
These two formats do not store the same things, and the difference is not cosmetic: styling, positioning and karaoke have nowhere to go in VTT. The list above comes from what the two formats can each express rather than from your file, so it is the same answer before you load anything.
One file is fine, and so is a whole season: the queue works through them in order and the results come down together as a single ZIP.
Examples
A typical JSON file, converted to VTT
Input
{
"version": 1,
"title": "Fixture: typical",
"fps": 25,
"styles": {
"Default": {
"name": "Default",
"fontFamily": "Arial",
"fontSize": 20,
"primaryColor": "#FFFFFF",
"bold": false,
"italic": false
}
},
"generator": "subtitlematrix fixtures",
"cues": [
{
"id": "1",
"start": 0,
"end": 2000,
"lines": [
"Hello world.",
"Second line."
],
"style": "Default",
"position": {
"x": 100,
"y": 200,
"align": "center"
}
},
{
"id": "2",
"start": 2500,
"end": 4000,
"lines": [
"Plain line.",
{
"text": "Styled line.",
"tags": [
{
"kind": "italic",
"start": 0,
"end": 6
}
]
}
]
},
{
"id": "3",
"start": 4500,
"end": 6000,
"lines": [
"Roger: I am here."
],
"speaker": "Roger"
}
]
}
Output
WEBVTT
1
00:00:00.000 --> 00:00:02.000
Hello world.
Second line.
2
00:00:02.500 --> 00:00:04.000
Plain line.
<i>Styled</i> line.
3
00:00:04.500 --> 00:00:06.000
Roger: I am here.
Dropped in this output: styling, positioning and karaoke. Everything else matches line for line.
The same conversion on an awkward input
Input
[
{ "start": 0, "end": 1000, "lines": ["First."] },
{ "start": 1000, "end": 2000, "text": "Second." },
"not an object",
{ "start": 2000, "end": 3000, "lines": ["Third."], "class": "top" }
]
Output
WEBVTT
00:00:00.000 --> 00:00:01.000
First.
00:00:01.000 --> 00:00:02.000
Second.
00:00:02.000 --> 00:00:03.000
Third.
This is the kind of damage real files have — mixed line endings, stray whitespace, fields left empty. Compare it with the tidy example above to see what the parser forgives.
Frequently asked questions
Which styling survives from JSON into VTT?
Emphasis, written into the text as tags: bold, italic, underline and a colour come out as `<b>`, `<i>`, `<u>` and `<font color="…">`, which browsers act on. What the VTT file will not carry is the style table JSON relies on — the font, its size, the outline, the shadow and the margins all go, and the page embedding the subtitles styles them from its own CSS instead.
What happens to the on-screen position from JSON to VTT?
VTT cannot say where a subtitle is drawn, so the position stored with each cue is dropped on the way out of JSON, and every cue goes back to the default position the player chooses — the bottom of the frame, centred, for most of them.
What happens to karaoke timing from JSON to VTT?
The timing goes; the words stay. Karaoke lives in the karaoke spans a JSON cue carries, which mark when each syllable lights up, and VTT has no way to record a moment inside a line — so the marks come off and the syllables arrive as ordinary VTT text.
What does the output look like when JSON becomes VTT?
Like VTT: an optional identifier line above each cue, which no player ever displays. Every JSON cue becomes one VTT cue, in the same order, with the same text.
Are the JSON timings exact in the VTT file?
Yes, to the millisecond — which is as fine as either format goes. JSON writes a moment as `4126` and VTT writes the same moment as `00:00:04.126`; nothing is rounded or shifted between the two, and a cue that was on screen for 2.9 seconds still is.
How does a two-line JSON cue come out in VTT?
As two lines, one under the other. The pairing survives — the two JSON lines still belong to one subtitle in the VTT output, and a player shows them together.
Do JSON cues keep their order in the VTT output?
Yes, and they are sorted by start time on the way — earliest first, which is how every format here expects them and how players read them. If your JSON file listed its cues out of sequence, the VTT output puts them back in order; that is a change to the file's structure rather than its content, and it is deliberate.
Can I convert the VTT back to JSON?
Yes, and it has its own list: converting VTT to JSON drops format-specific content. That list is different from the one above because the two formats keep different things.
Does the VTT output keep the JSON file's encoding?
No — the output is UTF-8, with Unix line endings and no byte-order mark, whatever the JSON file used. A file that arrives in UTF-16, or in a Windows single-byte encoding, is decoded on the way in (the result panel says so when that happens); what comes out is always the same UTF-8 VTT.