Burned-In Subtitles API

Captions baked into the frames — not a sidecar track

ZapCap renders styled captions permanently into the video itself and hands back a finished MP4. On TikTok, Reels, Shorts, and paid social, subtitle tracks get stripped or stay off by default. Burned-in captions always show — and they show in your style, not the platform default.

Create API key Read API docs

Open captions in the frames · h264 MP4 · webhook-native · usage-based credits

Workflow Demo Styling Transcripts Output modes Languages Pricing Proof Quickstart FAQ

Open captions vs everything else

Why "burned-in" and not a subtitle file

A subtitle track is optional — the player decides whether to show it. Burned-in captions are part of the picture, so they survive re-uploads, downloads, and silent autoplay.

OPTION 01

Soft subtitle file

SRT / VTT sidecar

Player decides if it shows
Stripped on most social re-uploads
No styling control
Off by default in feeds

OPTION 02

DIY ffmpeg burn-in

Self-hosted render workers

You build font + layout logic
You run the GPU/queue infra
You handle line-breaking
No preset styling

OPTION 03 · YOU ARE HERE

ZapCap · burned-in rendering

Finished MP4, styled captions baked in

Captions permanent in the frames
Styled presets or full overrides
h264 MP4 ready for any platform
Webhook-native, no render infra

OPTION 04

Video automation

Creatomate · Shotstack · JSON2Video

Full video generation
Build the whole timeline
Captions are one of many layers
Heavier integration to add captions

API workflow

From upload to burned-in MP4

Upload a clip, create a render task with a templateId, and collect the finished MP4 from the task status — or get a webhook. ZapCap handles transcription, styling, and the burn-in render.

1
Upload your video
POST the file to /videos. We stream it to storage and hand you back a videoId.
POSTPOST /videos
2
Create the captioning task
One POST starts transcription, styling and rendering with your chosen template. Add a notification webhook to skip polling.
POSTPOST /videos/:id/task
3
Receive the webhook
We POST status updates to your endpoint as the render moves through transcribing → rendering → completed.
HOOKPOST → your URL
4
Download the finished render
Burned-in subtitles, served from a global CDN. No watermark. MP4 ready for any social platform.
GETGET renderUrl

Step 1 / 4·~2s

1import { readFileSync } from "node:fs";

3const form = new FormData();

4form.append(

5 "file",

6 new Blob([readFileSync("clip.mp4")]),

7 "clip.mp4",

8);

10const { id: videoId } = await fetch(

11 "https://api.zapcap.ai/videos",

12 {

13 method: "POST",

14 headers: { "x-api-key": process.env.ZAPCAP_KEY! },

15 body: form,

16 },

17).then(r => r.json());

POST /videos·Upload your video

Live render

One source clip, four burned-in looks

Each MP4 below is the same source rendered against a different templateId. Captions are baked into the pixels — nothing relies on a subtitle track being honored downstream.

Beast preset

Hormozi preset

Tracy preset

Devin preset

Source is a 9:16 vertical clip. Because captions render into the frames, the output plays correctly on any platform, in any player, with sound off.

Styling as an API primitive

Brand the burn-in

Down to the keyword.

Send a templateId for a complete look, or override individual renderOptions so the baked-in captions match your brand. Because the styling is committed to the frames, get it right before the render — every control is a request field.

Templates — Beast, Hormozi, Tracy, Devin, plus 25 more (29 presets) — each preset is a finished burned-in look.
Keyword emphasis — flag punchwords; ZapCap colors / scales / boxes them so the hook lands in-frame.
Font & shadow — fontUppercase, fontShadow none / s / m / l for legibility over busy footage.
Layout — words per cue, vertical position with safe-zone math so captions clear platform UI.
Aspect ratios — render 9:16, 1:1, 16:9 burned-in outputs from one source.

Try a style

Render options

{
  "templateId": "46d20d67-255c-4c6a-b971-31fddcfea7f0",
  "renderOptions": {
    "subsOptions": {
      "emphasizeKeywords": true,
      "animation": true,
      "displayWords": 3
    },
    "styleOptions": {
      "fontUppercase": true,
      "fontShadow": "l"
    }
  }
}

Two transcript paths

Auto-transcribe — or burn in your approved cues

Auto-transcribe

ZapCap transcribes, splits, and times captions for you. Review the cues on the task status, edit them, then trigger the burn-in render against the approved transcript.

Inspect the transcript on the task status, edit via PUT /videos/:id/task/:taskId/transcript
Fix any wording before it is committed to the frames
Re-render the same transcript into multiple branded styles

Bring your own transcript

Already have approved copy? Send your own cues and ZapCap burns them in verbatim — no retranscription, no surprise wording in the final pixels.

Supported via the SRT-to-burned-in workflow
Lock in approved product names, claims, and disclaimers
Burn the same script into N looks for A/B ad variants

Output

Burned-in is the default — alpha and green-screen when you need them

Default

Burned-in MP4

Styled captions permanently rendered into the source frames. Survives re-uploads, downloads, and silent autoplay — the right choice for TikTok, Reels, Shorts, and ad creative.

.mp4 · h264

Editor-friendly

Transparent overlay

Need to composite captions over your own edit instead? Request an alpha-channel overlay and drop it onto a timeline — no chroma key.

.mov ProRes 4444 · .webm VP9 alpha

Compatibility

Green-screen layer

For tools that don't support alpha. Caption layer on a #04F404 canvas you key out in OBS, a switcher, or your NLE.

.mp4 · #04F404 backdrop

Burned-in (open) captions are the right call for social and ad distribution. For accessibility, where viewers must toggle captions on and off, pair the MP4 with an exported SRT/VTT.

Multilingual burn-in

Burn captions in the viewer’s language

Set a target language on the task and ZapCap transcribes, translates, and burns captions in that language. CJK and Thai use language-aware line-breaking, so wrapped lines look right baked into the frames.

Source in one language, burned-in captions in another
A brand-term dictionary keeps product names accurate before they are committed to the frames
Language-aware layout for Chinese, Japanese, Thai

Watch this part

看这一段

ดูตรงนี้

Simple API credits

Per-minute, usage-based credits

Pay for the minutes you render. Burned-in MP4 is the base rate; higher resolutions and alpha outputs use different multipliers — see pricing for the full table.

Top up credits to keep renders flowing in production
Volume credits available at scale
No per-seat fee — pay for renders, not users

$0.10 / min

Indicative starting rate. Final pricing depends on render mode and output format. API access requires a Pro plan plus credits.

View full pricing Talk to us about volume

Customer · Anonymized

A performance-marketing team standardized burned-in caption styling across every ad variant by routing renders through the ZapCap API

Instead of hand-editing captions per cut, the team submits one transcript and renders branded, burned-in MP4s for each hook test. Captions land identically on every platform because they live in the frames.

Read case study

in-frame

Captions survive every re-upload

1 source

Rendered into multiple hook variants

webhook

No polling, no manual exports

on-brand

Same style across all platforms

Developer quickstart

Render burned-in subtitles from a task request

The default render task returns a finished h264 MP4 with captions baked into the frames. Add a webhook notification when you want delivery pushed into your pipeline.

POST /videos uploads the source clip and returns videoId
POST /videos/{videoId}/task with templateId starts the burn-in render
The completed task returns downloadUrl for the captioned MP4

VIDEO_ID=$(curl -s -X POST "https://api.zapcap.ai/videos" \
  -H "x-api-key: $ZAPCAP_KEY" \
  -F "file=@clip.mp4" | jq -r .id)

TASK_ID=$(curl -s -X POST "https://api.zapcap.ai/videos/$VIDEO_ID/task" \
  -H "x-api-key: $ZAPCAP_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "templateId": "46d20d67-255c-4c6a-b971-31fddcfea7f0",
    "autoApprove": true,
    "language": "en",
    "renderOptions": {
      "subsOptions": { "animation": true, "displayWords": 3 }
    }
  }' | jq -r .taskId)

curl -H "x-api-key: $ZAPCAP_KEY" \
  "https://api.zapcap.ai/videos/$VIDEO_ID/task/$TASK_ID"

About the Burned-In Subtitles API

Burned-in (or "open") subtitles are captions rendered permanently into the video frames, so they are part of the picture itself rather than a separate, toggleable subtitle track. Because they are baked into the pixels, they always display — even when a player ignores or strips subtitle files, and even with sound off.

Keep exploring

Start rendering burned-in captions through the API

Create a key on a Pro plan and buy credits in the dashboard.

Create API key Read API docs

Burned-In Subtitles API

Captions baked into the frames — not a sidecar track

Why "burned-in" and not a subtitle file

From upload to burned-in MP4

Upload your video

Create the captioning task

Receive the webhook

Download the finished render

One source clip, four burned-in looks

Brand the burn-in

Down to the keyword.