Subtitle — 21

This was the original standard for analog TV where captions were "hidden" in line 21 of the vertical blanking interval of the video signal. While robust, these captions are not customizable by the viewer in terms of font or color.

Reviewers and experts emphasize several key rules for high-quality subtitles: subtitle 21

Widely reviewed as the "best free subtitling tool," it has recently added features like AI audio-to-text (using Whisper or Vosk) and the ability to burn-in subtitles directly into the video. This was the original standard for analog TV

Include non-speech elements like [glass breaks] or [mysterious music] to ensure accessibility for the deaf and hard of hearing. A modern service named after the legacy standard

Keep text concise and on-screen long enough for a person to read comfortably.

Subtitles must align perfectly with the audio to avoid confusing the viewer.

A modern service named after the legacy standard that uses a hybrid AI-human approach for live events and streaming, focusing on high accuracy for niche industries.