Media diagnostics · Primary-source explanation; no UK IPTV implementation or account test. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Separate syntax and viewing quality
Two subtitle cues visible at the same time can look surprising, but that observation alone does not prove a malformed file. The format and the intended caption layout matter. Record the actual start and end times, selected track and player rather than deleting a cue solely because its interval overlaps another one.
Use the documented timing rule
The W3C WebVTT specification says different cues can overlap and orders cues by start time. That permits more than one timed item to be active during an interval. It does not guarantee that every possible layout is readable or that an overlap was intended by the subtitle author. Format validity and editorial quality are separate checks.
Work through a short hypothetical overlap
Imagine cueA runs from10to13seconds and cueB from12to15seconds. Both are active between12and13. The existence of that one-second overlap can be calculated directly. If the text represents simultaneous speakers or another intended presentation, removing a cue may lose information. If it is accidental, the correction should be based on the actual sound and required layout, not a blanket no-overlap assumption.
Verify the specific output
Test an authorised sample in the intended player and inspect whether cues are positioned and distinguished usefully. Preserve the source while correcting only an authorised copy. Do not convert every overlap into a global delay or an account-support issue. This example explains a documented format allowance and original timing arithmetic; it reports no UK IPTV caption validation or universal accessibility pass.