Subtitle tools: convert, retime, merge and read caption files

Bearer key · JSON

POST /api/v1/subtitles

curl -s -X POST https://getattest.com.au/api/v1/subtitles \
  -H "authorization: Bearer $ATTEST_API_KEY" \
  -H "content-type: application/json" \
  -d '{"operation":"convert","to_format":"vtt","text":"1\n00:00:01,000 --> 00:00:03,500\nHello there.\n"}'

Send the key as a bearer token in the authorization header. One key and one credit balance cover every service, including Attest Capture. A failed call is refunded automatically. No key yet? POST /api/v1/keys issues one with 25 free credits and no signup — see the key guide.

Captured 2026-09-21

Example

This request was run against the running service on 2026-09-21 and the response below is what came back, unedited.

Request JSON

{
  "operation": "convert",
  "to_format": "vtt",
  "text": "1\n00:00:01,000 --> 00:00:03,500\nHello there.\n"
}

Captured response JSON

{
  "call_id": "3b3ddb5c-1d57-4066-9b8f-98f853e6dbd7",
  "operation": "convert",
  "from_format": "srt",
  "to_format": "vtt",
  "cues": 1,
  "duration_seconds": 3.5,
  "result_text": "WEBVTT\n\n1\n00:00:01.000 --> 00:00:03.500\nHello there.\n",
  "truncated": false,
  "applied": {
    "offset_seconds": 0,
    "scale": 1,
    "merge_gap_seconds": null,
    "strip_tags": false,
    "files": 1
  },
  "info": {
    "cues": 1,
    "characters": 12,
    "words": 2,
    "lines": 1,
    "first_start_seconds": 1,
    "last_end_seconds": 3.5,
    "total_cue_seconds": 2.5,
    "coverage_ratio": 1,
    "longest_cue_seconds": 2.5,
    "shortest_cue_seconds": 2.5,
    "max_characters_per_line": 12,
    "max_characters_per_second": 4.4,
    "overlapping_cues": 0,
    "zero_length_cues": 0
  },
  "warnings": [],
  "limits": {
    "max_file_bytes": 4194304,
    "max_file_base64_characters": 5592408,
    "max_text_characters": 4000000,
    "max_files": 20,
    "max_total_bytes": 8388608,
    "max_cues": 200000,
    "max_result_bytes": 2000000,
    "max_fetch_seconds": 120
  },
  "sources": [
    {
      "name": "W3C WebVTT: The Web Video Text Tracks Format",
      "url": "https://www.w3.org/TR/webvtt1/",
      "used_for": "WebVTT parsing and writing: the header, NOTE, STYLE and REGION blocks, cue identifiers, cue settings, the timestamp grammar and the cue payload tags"
    },
    {
      "name": "SubRip (.srt) — a de facto format with no published specification; the shape used here is the one every player accepts",
      "url": "https://en.wikipedia.org/wiki/SubRip",
      "used_for": "SubRip parsing and writing"
    },
    {
      "name": "Advanced SubStation Alpha (.ass/.ssa) — community specification, with the override tag list from the Aegisub manual",
      "url": "https://aegisub.org/docs/latest/ass_tags/",
      "used_for": "reading [Events] Dialogue lines, their H:MM:SS.cc timings and the \\N, \\n, \\h, \\i, \\b, \\u, \\p and \\r override tags"
    },
    {
      "name": "YouTube SBV (.sbv) — the caption format YouTube exports, H:MM:SS.mmm start and end joined by a comma",
      "url": "https://support.google.com/youtube/answer/2734698",
      "used_for": "SBV parsing"
    }
  ],
  "notice": "General information about the subtitle file you supplied. Timings are read from the file and transformed exactly as requested; nothing here checks the file against the video it belongs to. The file is processed in memory and is not stored.",
  "checked_at": "2026-09-20T16:55:57.516Z",
  "credits_charged": 1,
  "credits_remaining": 9989
}

For agents

Use when

Use this when a task involves a subtitle or caption file: converting between SubRip (.srt), WebVTT (.vtt), ASS/SSA and YouTube SBV, shifting timings or rescaling them for a frame-rate change (23.976 to 25 and back), merging several files onto one timeline, pulling a plain-text transcript out of captions, or reporting a file's cue count, duration and reading speed. The converted file comes back in result_text; the info operation leaves result_text empty and answers in the info block. Send the file as text, as a public URL, or as base64 up to 4 MB.

11 fields

Input

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HTTP 200

Response

Every successful response also carries call_id (your receipt for the charge), credits_charged and credits_remaining.

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Machine-readable failures

Errors

Errors return JSON such as {"error":"invalid_api_key"}. A failed call is refunded automatically.

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On every service

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6 worked examples

Examples

• SRT to VTT
• VTT to SRT
• Delay subtitles by two seconds
• Subtitles to plain text
• Merge SRT files
• Subtitle frame rate conversion 25 to 24 fps

Where the answer comes from

Source and scope

Written against the W3C WebVTT specification, the de facto SubRip format, the community Advanced SubStation Alpha specification and YouTube's SBV format; each response lists them in sources.

Attest reports what it read, with the source it read it from. It is general information, not advice, and not a legal record.

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