What it checks
Delivered subtitles must be listed in the order they appear on screen. Many playout systems read them one after the other and skip or mistime a subtitle that goes back in time.
How it is measured
CueNorm compares the start time of each subtitle with the start time of the one listed before it. A later subtitle may start at the same time, never earlier.
When it applies
Always, for every delivery profile: it is built in and cannot be removed or relaxed by a profile. It is an error. Mezzanine profiles do not apply it, since many source formats allow any order.
Example
A subtitle at 00:00:01,000 listed after one at 00:00:05,000 is reported as Starts before the previous subtitle — subtitles are not in chronological order.
How to fix
- Convert with the
SORT_SUBTITLEStransformation when the profile allows it: it reorders the subtitles by start time without changing them. - Or sort the subtitles in the authoring tool.