: For local files without subtitles, the Google Chrome browser has a built-in "Live Caption" feature that can generate text in real-time as you play the video through the browser.

If you already have the video files and need separate subtitle files to overlay, several reputable subtitle databases host community-verified English tracks for every season:

: If you need to follow along textually, the Adventure Time Wiki maintains full scripts of every episode.

: Official physical releases, including the complete series box sets, come equipped with English subtitle tracks. Independent Subtitle Files (SRT)

For those who prefer owning the series, subtitles are a standard feature on retail versions: