Performance creative localization API for ad caption variants
API-driven caption variants. Same hook, every market. Per-minute billing
Your winning creative is decaying in its home market while every other market sees nothing. ZapCap is the caption-rendering and translation API that spins a proven hook into localized variants from a single source clip, so the testing cycle keeps moving instead of waiting on an editor.
A winning concept should not stall in localization
Performance creative lives or dies on iteration speed. You found the hook that converts — but turning it into testable variants per market means editor tickets, translation turnaround, and re-renders. By the time the variants land, the auction has moved.
- Editor bottleneck — every variant queued behind a human in an NLE.
- Translation lag — agency turnaround measured in days, not test cycles.
- Hook consistency — the proven caption styling must survive the localization.
- Variant sprawl — one winner becomes dozens of cuts to track and label.
- Creative fatigue — the home-market winner decays while other markets wait.
- Attribution mapping — each rendered variant tied back to an ad set.
Where ZapCap sits in your creative-testing loop
Drop the API behind your creative-ops tooling. A winning source clip goes in; localized caption variants come back, labelled and ready to push into ad managers.
How the performance creative localization API works
Upload the winning clip once, then fire a render task per market with translateTo and a fixed caption preset. Each finished variant arrives via webhook, ready to label and push.
{
"eventId": "evt_8kQ2...",
"taskId": "tsk_2hP4...",
"event": "render.completed",
"renderUrl": "https://cdn.zapcap.../variant-es.mp4"
}- Map taskId → ad set / market when you create the task.
- Verify the x-signature header before fetching renderUrl.
- Dedupe webhook deliveries on eventId.
Lifecycle of a variant render
Each variant is an independent task. Track them so creative ops sees the test batch fill in and can push winners the moment they land.
Performance creative localization API launch checklist
A short list to keep variant generation fast and attributable. Creative ops, styling, and tracking in one place.
- Lock the winning caption preset One templateId reused across variants so you test market, not design.
- Keyword emphasis on Set subsOptions.emphasizeKeywords so the proven hook still pops per language.
- Variant ↔ ad-set mapping Store taskId against the ad set so attribution survives the render.
- Market list driven from config Add a market and the next batch picks it up automatically.
- Webhook signature verified Check x-signature on every payload; dedupe on eventId.
- Credit-balance check before a batch A variant batch is many renders — confirm balance before firing.
- Auto-push or review gate Decide whether finished variants go live or wait for a human OK.
The variant pipeline, honestly
In-house variant generator
- 1ASR + translation wiring — vendors, retries, terminology control.
- 2Caption styling engine — reproduce the winning look per language.
- 3Keyword emphasis logic — keep the hook prominent across scripts.
- 4Render workers — ffmpeg / libass, autoscaling for test bursts.
- 5Variant tracking — one winner, many labelled cuts, attribution.
- 6Output storage — pre-signed URLs, expiry, cleanup.
- 7Billing meter — per-minute counters across batches.
Variants as a primitive
- 1POST /videos — upload the winner once.
- 2translateTo per task — a localized variant per market.
- 3Webhook handler — verify, label, push.
A growth team wired the ZapCap API into their creative-ops tooling and now spins a proven winner into localized variants without an editor in the loop
Finding the winner is still the hard part — but turning it into testable variants per market is now an API call instead of an editor ticket, so the testing cycle keeps pace with creative decay.
For performance marketers
Pick one templateId from GET /templates as your locked caption preset and reuse it on every task. The styling — font, colour, animation, placement — stays identical while translateTo changes the language, so you are testing the market and the message rather than the caption design. The preset travels with every task you send to ZapCap’s video captioning API.
Turn on renderOptions.subsOptions.emphasizeKeywords so emphasised words keep their prominence in each localized cut. The translated text is rendered with the same emphasis treatment as the original winner.
Each variant is its own render task that returns a finished MP4 via webhook — no editor in the loop. Render time scales with clip length and is billed from $0.10/min base usage pricing; we do not publish throughput or turnaround guarantees.
Store the mapping yourself: when you create the task, save the returned taskId against the ad set or market in your own database. The webhook payload includes that taskId, so you can attribute the finished variant on a quick lookup.
Upload the winner once with POST /videos, then create one task per market — each with its own translateTo. They render independently, so a failure in one market never blocks the rest of the batch.
Use ZapCap to localize and caption proven creative, and pair it with a video automation API for data-driven assembly. Our honest comparison pages map out who beats us on which dimension.
Build the rest of the creative pipeline
E-commerce video localization API
Localize product video ads at scale from one source clip.
TikTok Shop video localization API
9:16 safe-zone-aware caption variants for cross-border social commerce.
Multilingual subtitle rendering API
The script-layout layer behind localized variants across many languages.
Agency video captioning API
Multi-tenant delivery: a stored caption preset per client, to a white-label portal.
AI video SaaS captioning API
The same backend pattern, framed for product teams embedding captions in their app.
Keep the testing cycle moving
Backend-only API, webhook-native, from $0.10/min base usage pricing. One winner in, a localized variant per market out — no editor in the loop.