Captions or AI

How mode decides where the transcript comes from.

A transcript comes from one of two sources:

Source	Speed	Uses AI hours
The video’s captions	Usually a few seconds	No
AI transcription	Slower	Yes

Captions come from the creator or the platform. AI transcription works on anything with speech.

Choose a mode

mode	What happens
auto (default)	Captions if the video has them, AI transcription if it doesn’t.
native	Captions only. A video without them returns CAPTIONS_UNAVAILABLE.
generate	Always AI transcription, even when captions exist.

Only YouTube, X and LinkedIn videos can have captions. Instagram reels, Facebook videos and files never do, so auto always transcribes them with AI and native returns CAPTIONS_UNAVAILABLE.

Language

lang takes a code like en, de or es-US.

Source	What lang does
Captions	Picks the caption track. If there’s no track in that language, you get LANGUAGE_NOT_AVAILABLE with availableLangs.
AI transcription	Tells the model which language is spoken. Leave it out and the language is detected.

Every transcript includes its language (lang) and the video’s caption languages (availableLangs).

AI transcription limits

Limit	Max	Error
Media length	2 hours	VIDEO_TOO_LONG
File size	2 GB	FILE_TOO_LARGE

Captions have no length limit. A 5-hour YouTube video with captions works with mode=native.

See Usage and limits for how AI hours are counted.