Start with the same video base name
An external caption file belongs beside the video it describes, with the same base filename before the additional subtitle information and extension. Compare the actual names, including punctuation and spaces, rather than only the title shown on a poster. A descriptive file elsewhere in the folder is not enough to establish the documented association.
Use Emby’s documented tokens for the real track
Emby lists language forms such as a language name or code, alongside role tokens. Its naming guide recognises .default, .forced or .foreign, and .sdh. It also documents region-qualified Chinese language forms where a generic language label would not distinguish the intended written variant. These labels need to reflect the existing file. Calling a full transcript forced, or labelling dialogue-only subtitles SDH, does not change what the file actually contains.
Check the selection in a small example
For example, an original short named Harbour.mkv could have a supplied Spanish subtitle file named Harbour.spa.srt. Use additional documented flags only when their meaning is accurate for that track. Keep a note of the old filename before changing it, then inspect the item’s subtitle choices after the appropriate library update. Select each relevant track and check that the displayed language and role match the material. If the track is recognised but its text is wrong or mistimed, treat that as a content or timing problem rather than continuing to rename it. This keeps file association, track description and playback verification as separate checks.
Questions, answered
Does adding .sdh create hearing-impaired captions?
No. It labels the track; the file must already contain the appropriate caption information.