#AI Captions

#Overview

Transcodely can transcribe a video’s audio track into a caption file automatically, using the generate subtitle operation. It runs on the same worker fleet that encodes your video — the audio is transcribed in-house, not handed off to a third-party captioning service, and it composes with the rest of the pipeline (HLS/DASH packaging, other subtitle tracks, thumbnails).

Generated captions are always labelled as machine-produced. Transcodely makes no accuracy guarantee — see Honesty markers for exactly how that is surfaced.

For the full wire contract — fields, formats, validation — see the Subtitles reference.

#Two ways to add captions

#1. Caption a new transcode

Add a generate track to any output that has audio when you create the job. In the dashboard’s new-job flow (and the uploader), this is the Auto-generate captions checkbox; on the wire it is a single subtitle track:

{
  "subtitle_tracks": [
    { "operation": "generate" }
  ]
}

#2. Retro-caption an already-hosted video

You do not need to re-encode a video to caption it. Point a captions-only job at a hosted video with input_video_id — no video variants, no re-encode:

{
  "input_video_id": "vid_a1b2c3d4e5f6g7",
  "outputs": [
    { "subtitle_tracks": [{ "operation": "generate" }] }
  ]
}

In the dashboard this is the Generate captions button on the video detail page. When the job finishes, the caption track appears there with an Auto-generated badge and a download link.

#Accessibility for your whole library (EAA)

The European Accessibility Act (EAA, Directive (EU) 2019/882) has been in force since 28 June 2025. New products and services must meet its accessibility requirements now, and content already in service — your back catalogue — has until 28 June 2030 to comply. For video, captions are a core part of that.

Retro-captioning is the back-catalogue play: input_video_id lets you caption videos you uploaded months or years ago without re-encoding them, one API call (or one button) at a time. Script it across your library and you get EAA-ready captions for your whole catalogue without touching your originals.

Captions help you meet accessibility obligations, but they are one requirement among several. Transcodely provides the captions; it does not certify overall EAA compliance for your product.

#Where your audio is processed

AI captions run on the same EU-based worker fleet that encodes your transcodes. The audio is transcribed in-house on that infrastructure — it is not sent to an external transcription API — so your media stays inside the Transcodely pipeline, consistent with how the rest of your encoding runs.

#Correcting a generated caption

Because captions are machine-produced, you may want to fix a word or a timestamp. There is no special edit endpoint — reuse the tools you already have:

1. Download the caption file from the track’s url (or the download link on the video page).
2. Edit it in any subtitle editor.
3. Re-attach it as a convert or passthrough track from source_url on your next job, replacing the generated one.

#Pricing

AI captions are an additive fee of €0.05 per minute of source video, metered on the input duration and charged once per job — the audio is transcribed once, no matter how many renditions you produce. Details:

• It is added on top of the encode cost as a fees line item on the job, shown in the dashboard cost breakdown as Encoding + Captions.
• It is exempt from the per-job minimum charge. That floor exists to recover the encoding VM’s cost; a separately metered service is never absorbed by it.
• The fee is only confirmed if a caption artifact is actually produced. No artifact, no charge.

See the pricing page for the full rate card and the calculator to estimate a captions bill.