Check Subtitle Minimum Duration
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The limit is not a number you type in: it is read out of a published document, and the report names that document, quotes the sentence it came from, says whether that sentence is a requirement or guidance, and gives the day we last verified it with a link. Pick the document you are answerable to. They do not agree with each other: Netflix counts characters per second and caps a line at 42 characters, while Ofcom and the BBC count words per minute and, on line length, the BBC caps a line at 37. Three of them state no figures at all — 47 CFR §79.1, WCAG 2.2 SC 1.2.2 and EN 301 549, which requires web pages and non-web documents to satisfy that same criterion. Those three require captions to identify who is speaking and to carry non-speech information, and leave every number to the broadcaster; a page that checks them asks whether the file does it, not whether some number is exceeded. They also do not carry the same weight: a defect that reads as a warning against WCAG reads as an error against EN 301 549, because the standard turns that criterion into a shall. Changing this box changes the limit and the citation together, so a report can never carry one document's number under another document's name. Pages that check something only one of these documents states offer only that one.
Which frame rate the timings are counted in. On the format pages this is what MicroDVD needs, because it stores timing as frame numbers. On the frame rate pages it is the rate the file was timed against — the version the subtitles were made for — and the page's second box takes the rate of the video you are going to use them with. 23.976, 24, 25, 29.97, 30, 50, 59.94 and 60 are the common ones. Getting it wrong shifts the whole timeline, and on the frame rate pages it shifts it by a ratio rather than by a fixed amount.
A cue that flashes past cannot be read, however few words are in it. This page measures how long each cue stays on screen and lists the ones shorter than the minimum in the Netflix Timed Text Style Guide, which is five sixths of a second. The file is read in your browser, never uploaded, and is not changed — what comes back is a report you can download as a PDF to read and keep, or as a CSV to sort in a spreadsheet.
The limit is 834 milliseconds, and the awkward number is the point. The style guide states it as five sixths of a second and glosses that as twenty frames at 24 frames per second. Five sixths of a second is 833.33 milliseconds, and timings are held here as whole milliseconds, so the limit is rounded up. Rounded down to 833, a cue measuring exactly 833 ms — genuinely shorter than five sixths of a second — would pass. Rounded off to 800, which is how the figure is sometimes summarised elsewhere, every cue between 800 and 833 milliseconds would pass as well.
The report says three things a threshold you typed in could not. It names the cue, prints the duration it measured and the limit it was compared against, and cites the sentence the limit came from, along with the day that sentence was last verified. It also lists what this page does not check. And on a MicroDVD file, whose timings are frame numbers rather than times, it prints the frame rate it used, because every duration in that report was quantised to a frame when the file was read.
Examples
A cue on screen for 800 milliseconds
Subtitles
1
00:00:01,000 --> 00:00:01,800
Where were you?
2
00:00:03,000 --> 00:00:05,000
I was working late.
What the report finds
Cues below the minimum duration — 1 found
Severity Cues Start End Measured Limit Clause
Warning 1 00:00:01.000 00:00:01.800 800 ms 834 ms Netflix Timed Text Style Guide: General Requirements — Duration: minimum duration 5/6 second (20 frames at 24fps)
Checked against
Standard: Netflix Timed Text Style Guide
Limit: 834 ms
Where it is stated: Duration: minimum duration 5/6 second (20 frames at 24fps)
Stated as: Guideline
Not checked by this page: Duration: maximum duration 7 seconds; Reading speed: 20 characters per second for adult content (17 for children's); Line length: maximum 42 characters per line (43–44 only in rare exceptions); Line length: maximum 2 lines per subtitle eventThe first cue is up for 800 ms and is reported; the second lasts two seconds and is not. Each row carries the measured duration, the limit and the sentence the limit was read from, and the basis section underneath adds which document that sentence lives in, whether it is a requirement or guidance, and the day it was verified.
Five sixths of a second, to the millisecond
Subtitles
1
00:00:01,000 --> 00:00:01,834
Where were you?
2
00:00:03,000 --> 00:00:03,833
I was working late.
What the report finds
Cues below the minimum duration — 1 found
Severity Cues Start End Measured Limit Clause
Warning 2 00:00:03.000 00:00:03.833 833 ms 834 ms Netflix Timed Text Style Guide: General Requirements — Duration: minimum duration 5/6 second (20 frames at 24fps)
Checked against
Standard: Netflix Timed Text Style Guide
Limit: 834 ms
Where it is stated: Duration: minimum duration 5/6 second (20 frames at 24fps)
Stated as: Guideline
Not checked by this page: Duration: maximum duration 7 seconds; Reading speed: 20 characters per second for adult content (17 for children's); Line length: maximum 42 characters per line (43–44 only in rare exceptions); Line length: maximum 2 lines per subtitle eventThe first cue is exactly 834 ms and passes; the second is 833 ms, one millisecond under, and is reported. That one-millisecond gap is what this example exists for: five sixths of a second has to be rounded somehow, and rounding it down passes cues that really are too short.
A file whose timings are frame numbers
Subtitles
{1}{1}25
{25}{45}Where were you last night?
{100}{150}I was working late.
What the report finds
Cues below the minimum duration — 1 found
Severity Cues Start End Measured Limit Clause
Warning 1 00:00:01.000 00:00:01.800 800 ms 834 ms Netflix Timed Text Style Guide: General Requirements — Duration: minimum duration 5/6 second (20 frames at 24fps)
Checked against
Standard: Netflix Timed Text Style Guide
Limit: 834 ms
Where it is stated: Duration: minimum duration 5/6 second (20 frames at 24fps)
Stated as: Guideline
Not checked by this page: Duration: maximum duration 7 seconds; Reading speed: 20 characters per second for adult content (17 for children's); Line length: maximum 42 characters per line (43–44 only in rare exceptions); Line length: maximum 2 lines per subtitle eventA MicroDVD file, where a cue is a pair of frame numbers rather than two times. Frames 25 to 45 at 25 frames per second is 1000 ms to 1800 ms, so 800 ms on screen, and it is reported; the second cue is exactly two seconds and is not. The report header prints the frame rate, without which none of the durations in it could be reproduced anywhere else.
Frequently asked questions
Why is the minimum duration on this page 834 milliseconds and not 800?
Because the document states five sixths of a second, with twenty frames at 24 frames per second as its gloss, and five sixths of a second is 833.33 milliseconds. Timings are held as whole milliseconds, so the limit is rounded up to 834: rounding it down to 833 would let a cue that is genuinely shorter than the stated minimum pass, and 800 — a figure that circulates in some third-party summaries — would let everything between 800 and 833 through as well.
Which document does the minimum-duration limit come from here?
The Netflix Timed Text Style Guide: General Requirements, which is the only one of the documents in this category that states a minimum cue duration. It is guidance published to Netflix's suppliers rather than law, and the report labels it that way in a row of its own. If your work is answerable to a different house style, its minimum is not in this archive and this page cannot check against it.
Is a cue of exactly 834 milliseconds reported?
No. The comparison is strictly less than the limit, so a cue sitting exactly on it is inside it. That is the same judgement call the maximum-duration page makes in the other direction, and it is why both boundaries are pinned by an example of their own: a comparison written the wrong way round either flags every correctly timed cue in a file or passes one that breaks the rule.
Why does the report print a frame rate for my MicroDVD file?
Because a MicroDVD cue is a pair of frame numbers and nothing else, so every timestamp in the report came from dividing those frames by the frame rate the page used. Change that number and every duration in the report changes with it, so the report names it rather than leaving you to work out which assumption was made.
Does checking minimum duration change my subtitle file?
No. The file is measured and left alone, and nothing is uploaded. If you want short cues actually lengthened, that is a different tool that writes a new subtitle file. This page tells you which cues are below the limit and by how much, which is the part you need before deciding what to do about them.
What if a cue is short on purpose?
Then it is still reported, and that is intended. A single word held for a third of a second, an interjection, a sound described in brackets: these are real cases, and a minimum duration is a readability floor rather than a statement about intent. The report lists what measured below the limit; whether a particular cue should be lengthened, merged with the next one or left as it is stays your decision.
What the check looks for
- The report describes a file, not a service. The Netflix style guide is a delivery requirement in Netflix's supplier contracts; it is not law, and nothing here says your subtitles satisfy it. The report states which cues measured below which published minimum, and names the limits in that document this page did not check.
- A minimum cue duration protects the viewer least able to compensate. A cue that is gone before the eye has landed on it cannot be recovered from memory, and viewers who read slowly, or who are reading in a second language, are the ones it costs. It is also the cheapest subtitle defect to fix and the easiest to leave in place, because a short cue plays without any visible glitch to prompt a second look.
References
- Netflix Timed Text Style Guide: General Requirements — duration: minimum duration 5/6 second, glossed there as 20 frames at 24fps.
- Netflix Timed Text Style Guide: General Requirements — this page takes the document's own wording, five sixths of a second; some published summaries of the same requirement give 0.800 second instead.