What it checks
Each subtitle has a number of visible characters. The table gives the reading time needed for a few character counts; a subtitle shown for less than the time its characters need produces one issue.
This is the rule of the French charter on the quality of subtitling for the deaf and hard of hearing (CSA, now Arcom, December 2011, criterion 6), which reasons in reading time per amount of text rather than in characters per second: 12 characters need 1 second, 20 need 2 seconds, 36 need 3 seconds and 60 need 4 seconds, with a 20 % tolerance.
How it is measured
- Characters are counted as in
MAX_READING_SPEED: visible characters, spaces and punctuation included, line breaks excluded. - Between two points of the table, the required time is interpolated linearly. Below the first point it is proportional (6 characters need half a second with the charter table); beyond the last point, the last slope continues (84 characters need 5 seconds).
- The tolerance applies to the characters: with 20 %, a subtitle of N characters counts as N ÷ 1.2 characters. With the charter table, up to 43 characters are accepted in 3 seconds.
- The charter gives only these four points and does not say how to read between them or how to apply the tolerance: the interpolation and the tolerance on characters are CueNorm's reading of it.
Parameters
| Parameter | Type | Meaning |
|---|---|---|
table |
mapping of character counts to durations | Reading time needed for each character count, increasing |
tolerance |
percentage (0–100) | Extra characters accepted before an issue is raised |
- id: MIN_READING_TIME
severity: warning
params:
table: {12: 1s, 20: 2s, 36: 3s, 60: 4s}
tolerance: 20
Example
Without tolerance, a 28-character subtitle needs 2.5 seconds (half-way between 20 characters in 2 s and 36 in 3 s). Shown for 2.499 seconds, it is reported as 28 characters need 2.500 s of reading time; shown 2.499 s.
The shipped French SDH profiles declare this rule as a warning, since the charter encourages these reading times rather than imposing them.
How to fix
- Extend the subtitle's out-time, if the next subtitle and the shot allow it.
- Condense the text.
- Merge the subtitle with its neighbour when both are short.