This feature determines each caption’s duration based on its length in characters, and with different values for short, medium and long captions. This is because short captions have a larger appear time per character than longer captions. Short captions are those with up to 5 characters, medium are those with 6 to 15 chars, and long ones have at least 16 characters.

By default, short captions have an appear time of 250 milliseconds per character and a tolerance of 100 milliseconds. The tolerance is per character as well, and not for the entire caption. See the following example:

We take a caption containing “Hi.” It will be treated as a short caption since it has 3 characters.

During subtitling process, this caption will be set to appear during: 250 x 3 = 750 milliseconds.

During subtitle file load, accordingly to the 100 ms tolerance, this caption can have a duration of either: (250 – 100) x 3 = 450 ms, or (250 + 100) x 3 = 1050 ms. Therefore, no correction would be applied for this caption while its duration is between the 450 to 1050 milliseconds range.

Only if the caption’s duration time per character is outside the established time plus its tolerance, (which in this case would be less than 450 or more than 1050 ms) a new duration will be set by multiplying the caption length by the current appear time per character. That is, 250 x 3 = 750 ms.