What This Tool Is For
Subtitles that look fine to the naked eye often turn out to have overlapping timelines, overly wide lines, or too-high reading speed once delivered. The QC page lists these issues one by one:
- Timing: overlaps, end earlier than start, too-short or too-long durations, broken numbering
- Layout: overly wide single lines, more than two lines, poor line-break positions, leading or trailing spaces
- Language details: missing spaces between CJK and Latin text, punctuation off the language norms, writing direction
- Hard defects: garbled or control characters, malformed timestamps
Pick the Language Rules First
Under “Check by which language’s rules” you set five thresholds: maximum single-line width (42 half-width units for landscape by default, 36 for square, 28 for portrait), reading speed limit (18 width-units per second for Chinese, Japanese and Korean, 20 for other languages), minimum duration of 833 milliseconds, maximum duration of 7000 milliseconds, and at most 2 lines. Set the subtitle language to auto-detect or pick one of the 27 manually; screen orientation only changes the line-width tier — reading speed, durations and line count stay as they are. Half-width units are the shared measure: one hanzi counts as 2, one Latin letter as 1 — a line width of 42 equals 21 hanzi or 42 letters.
Reading the Report
The 17 rules report findings at three levels: errors (garbled text, timestamp format, end earlier than start, broken numbering), warnings (empty entries, overlaps, too-short or too-long durations, reading speed over the limit, overly wide lines, more than two lines), and hints (line-break position, leading or trailing spaces, missing spaces, punctuation norms, and more). Each finding carries the entry number and a “measured X, threshold Y” detail, and the list can be filtered by level. Bilingual entries get exemptions: both forms are auto-detected, overlap checks exempt the whole pair, and reading speed counts only the line written in the target language.
Fixing and Exporting
The “Fix & export” card lists only auto-fixable items: rewrapping, removing empty entries, adding missing spaces, replacing punctuation per language norms, renumbering — everything that leaves the timing untouched is ticked by default; items that change timing (swapping start and end, shifting overlaps, trimming or stretching durations) are unticked by default — tick them after checking the impact yourself. Click “Apply fixes” and a fresh check runs automatically; the counter only counts what was genuinely fixed — lines that could not be rewrapped are not inflated into the numbers. Reading speed over the limit has no auto-fix: the machine cannot know which word to cut, so the translation has to be shortened by hand or the timing adjusted. After fixing, export SRT or VTT, or click “Download report” to save a plain-text `.qc.txt` report.
FAQ
Why can’t my ASS be exported? QC exports only SRT and VTT; ASS goes in but does not come out. To keep ASS effects, think it through at Format Converter first.
What does a reading speed of 18 mean? For Chinese, Japanese and Korean the cap is 9 full-width characters per second (18 half-width units); other languages get 20 half-width units per second. These are the common comfort tiers, and the input box lets you change them.
My file’s encoding is broken — can it still be checked? QC reads UTF-8 only; fix the encoding on the garbled-text repair page first.
Will it touch my timeline? Not as long as you leave the “changes timing” group unticked; even when ticked, every change is spelled out before the fix is applied.
Related Guides
Subtitles flashing by too fast to read — see the dedicated guide Subtitles Too Fast to Read. What to check before delivery — the checklist is at What to Check Before Delivery. A timeline that drifts out of sync is a different kind of problem — see Subtitles Drifting Out of Sync.