XMLTV is an open, XML-based file format used to describe TV listings — which program airs on which channel and when. It's the most common format behind the EPG data your player app displays.
What's inside an XMLTV file
Each entry typically includes a channel identifier, a program title, a start and end time, and often a short description. Player apps parse this data and match it to the corresponding channel in your playlist.
How it connects to your playlist
Your M3U playlist and your XMLTV guide are matched by channel identifiers behind the scenes, which is why both need to be entered — and occasionally refreshed — for a fully working guide.
Troubleshooting mismatched schedules
If programs seem misaligned with actual air times, a timezone setting mismatch in your player app is the most common cause, rather than an issue with the XMLTV data itself.