Subtitle 21 -

This is the newer digital standard. Unlike Line 21, it allows viewers to change the appearance of captions, such as text size and background transparency.

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. subtitle 21

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. This is the newer digital standard

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. A modern service named after the legacy standard

Include non-speech elements like [glass breaks] or [mysterious music] to ensure accessibility for the deaf and hard of hearing.