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

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.

These video reviews and tutorials demonstrate how modern software has evolved beyond legacy Line 21 captioning to provide AI-powered, animated subtitles:

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

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