Embedded subtitles vs separate subtitle files

Embedded subtitles are already built into the video file itself, while separate subtitles are downloaded files that the IPTV player overlays on the video independently.

Embedded subtitles

These are part of your provider's stream/file. They're available immediately with no extra download, but you're limited to whichever languages the provider included — often just one or two, or sometimes none at all.

Separate subtitles

You download these separately (for example via OpenSubtitles) and they're overlaid on the video independently. Advantage: far more language choice and the ability to manually adjust sync. Downside: you depend on whether a good upload is available for that specific title.

Can you combine them

Yes — both types can sit side by side in the same selection list. You pick which one to use each time, regardless of whether it's a built-in track or a downloaded file.