Subtitle Generator — From Video to Captions in One Step

Drop a video, get subtitles. No timecoding, no manual sync, no subtitle editor needed.

Description

Use this skill when the user wants to generate subtitles from video, auto-caption any clip, transcribe spoken audio, translate captions to another language, burn hardcoded text onto footage, or export SRT/VTT files. Powered by NemoVideo AI.

This skill covers the full subtitle pipeline: speech-to-text transcription with word-level timing, multi-language translation, styled burn-in rendering, and file export — all through a single chat interface.

Trigger phrases: subtitle generator, generate subtitles, auto subtitles, auto captions, caption generator, transcribe video, video to text, burn subtitles, hardcode captions, export SRT, SRT file, VTT export, bilingual subtitles, translate subtitles, add captions to video, closed captions, open captions, speech to text, video transcript

Primary use cases:

• Transcribe video/audio speech into timed subtitles (Whisper-powered, any language)
• Export subtitle files as SRT, VTT, or plain text transcript
• Translate generated or uploaded subtitles into any of 50+ target languages
• Burn styled captions directly into video (font, size, color, outline, position)
• Create bilingual dual-language subtitle overlays (e.g. English + Chinese)
• Batch process multiple clips with consistent caption styling
• Generate accessibility-compliant captions for social platforms

Not for: general video editing, video generation from text, or screen recording.

Setup

Base URL: https://mega-api-prod.nemovideo.ai

All requests require:

Authorization: Bearer <NEMOVIDEO_API_KEY>
Content-Type: application/json

Set NEMOVIDEO_API_KEY in your environment or OpenClaw secrets.

Workflow Overview

Upload video/audio → Start subtitle job → Poll status → Get SRT/VTT/transcript
                                                      → Burn subtitles into video

API Reference

1. Upload Media

Upload a video or audio file before processing.

POST /v1/upload
Content-Type: multipart/form-data

file=<binary>

Response:

{
  "file_id": "f_abc123",
  "filename": "interview.mp4",
  "duration_seconds": 182,
  "size_bytes": 45000000
}

Use file_id in subsequent requests.

2. Generate Subtitles (Transcription)

Transcribe speech and produce time-coded subtitles.

POST /v1/subtitles/generate
Content-Type: application/json

{
  "file_id": "f_abc123",
  "language": "en",
  "output_formats": ["srt", "vtt", "txt"],
  "options": {
    "punctuate": true,
    "max_chars_per_line": 42,
    "max_lines": 2
  }
}

Parameters:

Response:

{
  "job_id": "job_gen_789",
  "status": "queued",
  "estimated_seconds": 45
}

3. Translate Subtitles

Translate existing subtitles into a target language.

POST /v1/subtitles/translate
Content-Type: application/json

{
  "source": {
    "type": "job_id",
    "value": "job_gen_789"
  },
  "target_language": "zh",
  "preserve_timing": true,
  "output_formats": ["srt"]
}

Or translate from an uploaded SRT file:

{
  "source": {
    "type": "file_id",
    "value": "f_srt_456"
  },
  "target_language": "zh",
  "preserve_timing": true,
  "output_formats": ["srt", "vtt"]
}

Supported language codes: en, zh, zh-tw, ja, ko, es, fr, de, pt, ar, ru, hi, vi, th, id

4. Burn Subtitles Into Video

Hardcode captions permanently into the video frame.

POST /v1/subtitles/burn
Content-Type: application/json

{
  "file_id": "f_abc123",
  "subtitle_source": {
    "type": "job_id",
    "value": "job_gen_789"
  },
  "style": {
    "font": "Arial",
    "font_size": 28,
    "color": "#FFFFFF",
    "outline_color": "#000000",
    "outline_width": 2,
    "position": "bottom",
    "margin_bottom": 40
  },
  "output_format": "mp4"
}

Style parameters:

5. Bilingual Subtitles

Burn two subtitle tracks simultaneously.

POST /v1/subtitles/burn-bilingual
Content-Type: application/json

{
  "file_id": "f_abc123",
  "primary": {
    "subtitle_source": { "type": "job_id", "value": "job_gen_789" },
    "style": { "font_size": 26, "color": "#FFFF00", "position": "bottom", "margin_bottom": 70 }
  },
  "secondary": {
    "subtitle_source": { "type": "job_id", "value": "job_translate_321" },
    "style": { "font_size": 22, "color": "#FFFFFF", "position": "bottom", "margin_bottom": 30 }
  },
  "output_format": "mp4"
}

6. Poll Job Status

All jobs are async. Poll until completed or failed.

GET /v1/jobs/{job_id}

Polling strategy: every 3-5s for short files, 10-15s for longer ones. Timeout after 10 minutes.

7. Download Output

Download from the URL in job outputs. CDN URLs are pre-signed, valid 24 hours.

Common Workflows

A: Generate + Export SRT

Upload → generate (language: auto, formats: ["srt"]) → poll → download SRT

B: Translate Existing Subtitles

Upload SRT → translate (target: "es") → poll → download translated SRT

C: Full Pipeline (Video → Hardcoded Chinese Subtitles)

Upload video → generate (en) → translate (zh) → burn (zh) → poll → return MP4

D: Bilingual Video (EN + ZH)

Upload → generate (en) → translate (zh) → burn-bilingual → poll → return MP4

Error Handling

Behavior Notes

• Use language: "auto" when source language is unknown (+5s detection time)
• zh = Simplified Chinese, zh-tw = Traditional Chinese
• SRT is more universal; VTT for web players. When unsure, offer both
• Burning re-encodes the video — takes longer than SRT export alone
• File limits: 2GB upload, 4h max duration
• Output URLs expire after 24 hours

Example Prompts → Actions