Understand a subtitle reading-speed warning
Calculate characters per second and use it as an editorial signal without mistaking it for an accessibility certificate.
Start with the calculation
Characters per second, or CPS, divides the visible character count by the cue duration. A cue with 48 counted characters on screen for 3 seconds has a rate of 16 CPS. Showing the same words for 2 seconds raises the rate to 24 CPS.
CPS helps find cues that may need editorial attention. It does not measure vocabulary difficulty, competing visual information, or an individual viewer’s reading speed. A short unfamiliar name or technical expression can need more time than a longer familiar sentence.
| Input | Value |
|---|---|
| Counted text | 48 characters |
| Start | 00:00:10,000 |
| End | 00:00:13,000 |
| Duration | (13000 − 10000) ÷ 1000 = 3 seconds |
| CPS | 48 ÷ 3 = 16 |
Use the tool’s count as a reproducible measurement
Subtitle Workbench counts Unicode code points, including spaces and punctuation, and excludes line breaks. It removes common SRT b, i, u, and font tags before counting. It decodes the named entities amp, lt, gt, quot, apos, and nbsp; unrecognized markup and numeric entities are counted as written.
A Unicode code point is not always one displayed character. An accented character can use a combining mark, and one emoji can contain several code points. Word-based and character-based metrics also vary across languages. The result is a measurement under this method, not a universal reading standard.
Choose a threshold for the delivery context
The default 20 CPS, 42 characters per line, and one-second minimum duration are editable starting points for reviewing a file. They are not a streaming-service profile, broadcaster acceptance rule, or legal requirement. Use the delivery specification when one exists.
- Educational captions, children’s content, dialogue-heavy drama, and specialist training can call for different editorial decisions.
- The DCMP Captioning Key shows how timing, presentation, and language work together for educational media. It is not a hidden universal rule for every video.
Review the cue in the video
Watch the flagged cue in context. More duration can help when there is room, although extending into the next speaker or across a scene change can create a new problem. A natural line break can improve reading without changing the wording. Translation edits may need a qualified reviewer.
The checker does not paraphrase, split, merge, or extend cues. It shows the measurement and the relevant block. A file with no CPS warnings can still contain inaccurate text, missing sounds, poor speaker identification, or incorrect placement.