May relate to MC-221594.

The bug

The time for which sound subtitles are displayed on-screen is constant, meaning that for particularly long sound effects, the subtitle can disappear while the sound is still playing.

How to reproduce

1. Enable subtitles
2. /playsound minecraft:entity.ender_dragon.death block @p
3. Observe

Expected results

The subtitle would be visible for as long as this sound plays.

Actual results

It is not, and fades out before completion.

How to fix

Make sound subtitles display for a fixed minimum length (so that short sounds still have readable subtitles), but variable maximum length so that long sounds such as the ender dragon death sound have visible subtitles throughout playback.