Reels, Shorts, and one SRT
The same file, different chrome around it.
An SRT does not know which app will show it. The speed and line limits travel well. The safe zone does not. A caption that clears the bottom of a Short can sit under a username on a Reel, or the reverse, after a redesign.
Check the SRT once on checker, then look at the same cues in preview with a local video. Burned-in captions (text already in the picture) will not appear in the SRT. The preview only draws the cues from the file.
Spanish and Portuguese interfaces are a later pass. This version is English, which is the first market in the plan. The rules themselves are numbers, so a translated caption file can be checked here today.