Check your subtitles before delivery

• Characters a line: the longest line of each caption, counted without formatting tags such as <i>.
• Lines a caption: subtitle specs usually allow two.
• Characters a second: every character shown, spaces included, divided by the time on screen. Faster than the limit is hard to read.
• Shortest and longest on screen: a caption shorter than about a second flashes past; one held much longer than seven seconds tends to be read twice.
• Overlaps and gaps: a caption that starts before the last one ends overlaps it, and a gap of one or two frames between captions reads as a flicker.

The defaults are common in streaming and broadcast delivery: Netflix's English guide, for example, sets 42 characters a line, two lines, 20 characters a second for adult programmes and at least 5/6 of a second. Many other languages and specs use 17 characters a second, so set the limit to your own spec.

Download fixed SRT (or VTT) mends what timing can: it wraps long lines again, splits a caption with too many lines into two, holds short or fast captions longer where the gap after them allows, ends overlong ones at the maximum, and opens overlaps and tight gaps to the minimum gap. The words stay exactly as written, and the issue list shows what is left.

What it leaves is usually a caption with more words than its time allows: split it by hand, or cut words that the speech does not need.

In Cuecaps every word is a block on the waveform timeline, so you can drag a caption's start or end in 10 ms steps, set the words per caption, and export the SRT or VTT again.