What it checks
CueNorm picks the reader from the file extension (.srt, .stl, .ass, .vtt, .ttml/.xml/.dfxp…). When the content clearly belongs to another format — an SRT text saved as .stl, an EBU-STL file renamed .srt — reading it as the extension says would only produce meaningless errors, so the file is refused with a message naming both formats.
How it is measured
CueNorm looks for the signature of each format at the start of the file: the EBU-STL header (a disk format code STL25.01 or STL30.01 at byte 3), the WEBVTT header, an ASS [Script Info] section, an XML document whose root is tt, or an SRT cue (a number followed by a --> timing line). A file whose content matches none of them is read as its extension says and diagnosed by that reader.
When it applies
Always, for every file you validate, convert or import. It is fatal: the file is not processed (exit code 3 on the command line, 422 in the API).
Example
An SRT text saved as episode.stl is reported as The file is read as EBU-STL (from its extension) but its content is SRT: check the file or its extension.
How to fix
- Give the file the extension of its real format.
- Or check that you uploaded the intended file: an export may have been saved in another format than expected.