What it checks
In an EBU-STL file, each subtitle is stored in TTI blocks, and each block carries a Text Field of 112 bytes. The Text Field of the last block of a subtitle must end with the code 8Fh (EBU Tech 3264 §4.3.2), so a single block holds at most 111 bytes of text. When the text of a subtitle needs more room, it continues in extension blocks. Extension blocks are legal, but some ingest chains handle them poorly. A subtitle stored in more blocks than the profile allows produces one issue.
Only EBU-STL files are measured: other formats have no TTI blocks, so the rule never reports on them. When CueNorm converts to EBU-STL, the rule judges the generated file.
How it is measured
CueNorm counts the TTI blocks of each subtitle as stored in the file, the extension blocks included. The Text Field holds the text bytes, not characters:
- Every control code (colour, double height…) takes one byte.
- An accented letter can take two bytes in ISO 6937 (the Polish
ąis stored as a floating diacritic plusa).
A two-line Polish subtitle can therefore exceed 111 bytes while staying within the editorial character limits.
Parameters
| Parameter | Type | Meaning |
|---|---|---|
max |
positive integer | Maximum TTI blocks per subtitle; 1 means no extension block |
Example
With max: 1, two lines of 36 Polish accented letters need about 150 bytes and are reported as Text spans 2 TTI blocks (max 1): it does not fit in one 112-byte Text Field ending with 8Fh.
The shared EBU-STL teletext base declares this rule as info: the file stays valid. A destination whose ingest refuses extension blocks declares it again with severity: error.
How to fix
- Nothing is needed when the destination accepts extension blocks.
- Otherwise, shorten the text, or split the subtitle into two consecutive subtitles.