Feature Request: Export subtitles as a separate file

[meiiie]

Summary

Track support for exporting generated captions/subtitles as a separate subtitle file.

Motivation

Issue #227 combines two unrelated requests. Mouse click sound effects already have an extension path, while subtitle export is a separate feature request with a different implementation path and review surface.

Requested behavior

• Export subtitles/captions as a separate file alongside the video when available
• Likely formats to consider: SRT and/or WebVTT
• Keep this scoped to subtitle-file export, not inline caption rendering inside the video

Related

• Split out from Mouse Click Sound & Subtitle Export #227