Check your subtitles
Characters per second, line length, durations and overlaps, against the standard you pick.
A good subtitle is not just a well translated one: it has to be readable in the time it is on screen. The measure the whole industry uses is reading speed in characters per second (CPS). Above 17 CPS an adult starts losing text; above 20 they stop reading and just watch.
On top of that come other limits that exist for the same reason: no more than two lines, no more than 42 characters per line (so they fit on screen without shrinking the font), no less than five sixths of a second on screen (below that the eye does not even focus) and no more than 7 seconds (above that people re-read).
The tool compares your file against the standard you choose and lists the cues that break it, with their timing and the reason. The defaults follow the Netflix English style guide; change them if you work to a different spec.
How to use it
- 01 Load the subtitle file you want to check.
- 02 Pick a standard or set the limits by hand.
- 03 Go through the list of failing cues: each row gives the number, the timing and which limit it breaks.
- 04 Fix them in your editor and load it again to confirm.
Frequently asked questions
What are characters per second?
The number of characters in the cue divided by the seconds it stays on screen. It is the standard way of measuring whether there is time to read it. Netflix sets 17 CPS for adults and 13 for children content.
Why 42 characters per line?
It is the limit that lets the cue display on a television without shrinking the font or leaving the safe area of the picture. The BBC uses a percentage of screen width, which in practice lands around that number.
What counts as an overlap?
A cue starting before the previous one has ended. Players handle that differently: some cut it off, some stack it. Best to make sure it never happens.
Does it fix the problems automatically?
No. It only flags them, because fixing almost always means deciding which text gets shortened, and that is a translation decision, not a mechanical one.
Related tools
This is what Eco does live.
These utilities work on files you already have. Eco transcribes and translates while the audio is still playing: meetings, classes, videos in another language.
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