Check Subtitles Against the Netflix Timed Text Style Guide
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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.
Netflix's Timed Text Style Guide states four figures a subtitle file can be measured against — 20 characters per second for adult content, 42 characters on a line, a minimum cue duration of five sixths of a second, and a maximum of seven seconds — and this page runs all of them over one file in a single pass. The file is read in your browser, never uploaded, and is not changed. The report is downloadable as a PDF or as a CSV.
One section of the report will not be a table. The guide also states a line count: a subtitle event carries at most two lines. Nothing on this page checks that, and rather than leave you to find out by accident, the report names it under what was not checked. That list is short and it is deliberately not empty. Every figure the report does apply is printed with the sentence it came from and a link to the page it was read from, so a finding can be traced back without leaving the report.
The comparison worth making is with the same file checked against Ofcom's guidance. There, only the reading speed is measurable, because that document states nothing else; here, four sections carry findings. Both pages run the same five checks over the same bytes. What changes is the document, and with it the unit: Netflix counts characters per second where Ofcom counts words per minute, so a cue can pass on one page and fail on the other without either report being wrong.
Examples
One file measured against all four Netflix figures
Subtitles
1
00:00:01,000 --> 00:00:03,000
JOHN: I told you not to wait up.
2
00:00:04,000 --> 00:00:07,400
- I know what you did last summer, and I am not going to pretend otherwise.
- Then say it out loud, right here, in front of everybody.
3
00:00:09,000 --> 00:00:09,600
Wait.
4
00:00:11,000 --> 00:00:19,200
MARY: Nothing. It does not matter now.
5
00:00:21,000 --> 00:00:23,000
The quick brown fox jumps over the lazy dog every single morning.
What the report finds
Cues read faster than the limit — 2 found
2 | 00:00:04.000 | 00:00:07.400 | 39.1 CPS | 20 CPS | Netflix English Timed Text Style Guide (USA) — Reading speed: 20 characters per second for adult content
5 | 00:00:21.000 | 00:00:23.000 | 32.5 CPS | 20 CPS | (the same sentence)
Lines longer than the limit — 2 found
2 | 75 characters per line | 42 characters per line | Netflix Timed Text Style Guide: General Requirements — Line length: maximum 42 characters per line (43–44 only in rare exceptions)
5 | 65 characters per line | 42 characters per line | (the same sentence)
Cues below the minimum duration — 1 found
3 | 00:00:09.000 | 00:00:09.600 | 600 ms | 834 ms | Netflix Timed Text Style Guide: General Requirements — Duration: minimum duration 5/6 second (20 frames at 24fps)
Cues above the maximum duration — 1 found
4 | 00:00:11.000 | 00:00:19.200 | 8200 ms | 7000 ms | Netflix Timed Text Style Guide: General Requirements — Duration: maximum duration 7 seconds
Cues with two speakers and no name — Not applicable. This document says nothing about this, so there is no requirement to check against
Not checked by this page: Line length: maximum 2 lines per subtitle eventFour sections, four different figures, all from one document — and the last line, which is the one that separates a thorough report from a confident one. The two-line rule is a real line in the guide and no page on this site checks it, so it is listed rather than dropped. Cue 2 fails on three counts at once, and that is normal: a cue with two lines of dialogue at 40-odd characters each is over the reading rate, over the line length and inside the duration rules. Each finding quotes the sentence it was measured against, so you can see which part of the guide to look at when deciding what to change.
Every figure approached but not exceeded
Subtitles
1
00:00:01,000 --> 00:00:04,000
Sphinx of black quartz, judge my vow now.
2
00:00:05,000 --> 00:00:05,834
Yes.
3
00:00:07,000 --> 00:00:14,000
No.
4
00:00:16,000 --> 00:00:18,000
This cue holds exactly forty characters.
What the report finds
Cues read faster than the limit — Nothing found.
Lines longer than the limit — Nothing found.
Cues below the minimum duration — Nothing found.
Cues above the maximum duration — Nothing found.Each cue sits exactly on a boundary and none is reported. The last one is forty characters in two seconds: twenty characters per second on the nose, and the comparison is strictly greater than the limit. The short cue is 834 milliseconds, exactly the stated minimum. The long one is exactly seven seconds. This is what makes the difference between a report that reads clean and a page that reports flapping edges: move any of those cues by a single character or a single frame and findings appear.
Frame-based subtitles, where a duration only exists once a frame rate is given
Subtitles
{1}{1}30
{30}{48}Where were you last night?
{300}{540}I was working late, and I did not want to call you at that hour.
What the report finds
File: episode.sub
Format: MicroDVD
Cues: 2
Frame rate: 30
Cues read faster than the limit — 1 found
1 | 00:00:01.000 → 00:00:01.600 | 43.3 CPS | 20 CPS
Cues below the minimum duration — 1 found
1 | 600 ms | 834 ms
Cues above the maximum duration — 1 found
2 | 00:00:10.000 → 00:00:18.000 | 8000 ms | 7000 ms
Lines longer than the limit — 1 found
2 | 64 characters per line | 42 characters per lineMicroDVD stores frame numbers, not times, so every figure on this page depends on the frame rate in the panel — 30 in this example, which is what turns the first cue into 600 milliseconds and the second into eight seconds. The rate is printed at the top of the report, because a report that measured durations without saying which frame rate produced them would be unreadable a week later. The same file at 25 frames per second reports different durations and can reach a different verdict, which is not a defect: it is what frame-based files mean, and the first line of the file, which in MicroDVD declares a frame rate, is not counted as a cue.
Frequently asked questions
Which Netflix figures does this page apply to one file at a time?
Four. Twenty characters per second for adult content, from the English Timed Text Style Guide; a maximum of 42 characters per line, a minimum cue duration of five sixths of a second and a maximum of seven seconds, all from the General Requirements page. The guide states a fifth rule — at most two lines per subtitle event — and no page here checks it, so the report lists it under what it did not check instead of leaving it out.
What is the Netflix rule the report lists as not checked?
A maximum of two lines in a subtitle event. It is a real line in the General Requirements page and it is absent from this report's tables, so it is named in the closing section with the sentence it appears in. An unreported check that nobody mentions is the kind of gap that only shows up when a reviewer asks why a three-line cue was not flagged; one line of output is cheaper than that.
Netflix counts characters per second. Why does the same file get a different reading speed on the Ofcom page?
Because the two documents measure different things: Netflix counts characters, Ofcom counts words separated by whitespace. Neither page converts into the other's unit, since the conversion needs an assumed average word length and would produce a figure no document states. Both measurements are correct for the document they come from, and a file can be inside one and outside the other. If you are answerable to both, run both and treat each report against its own document.
Why does the Netflix minimum cue duration read 834 milliseconds rather than 800?
Because the guide states five sixths of a second, qualified as twenty frames at 24 frames per second, and that is 833.33 milliseconds repeating. Rounded up to the nearest whole millisecond, the limit is 834, which is what this report compares against, so a cue of exactly 834 milliseconds is inside it. The alternative transcription of the same rule that circulates as 0.8 seconds is 33 milliseconds stricter and would report cues the guide allows. The report prints the limit it used on every finding.
Does the Netflix Timed Text Style Guide say anything about identifying who is speaking?
Not in the pages this check applies. The speaker section of this report reads that the document says nothing about this, so there is no requirement to check against. Identification is stated as a duty by WCAG 2.2 Success Criterion 1.2.2 and by the FCC caption quality rules, and both of those have pages of their own. A Netflix report that showed a clean speaker table would be implying the guide had a rule where it has none.
Do the Netflix figures carry the same weight as a regulation?
No. They are a delivery specification a content owner states for the material it accepts, and the report labels every one of them as guidance in the row that says how the sentence is stated. That is worth having on the page: a figure that reads like a legal threshold when it is a contractual one changes what people do with the report, and the difference is invisible unless the report says which it is.
What the check looks for
- The report describes a file, not a service. The Netflix Timed Text Style Guide is a delivery specification that a content owner sets for material it accepts; it is not legislation, and passing or failing these checks is not a statement about legal compliance anywhere. Nothing here concludes that your subtitles comply with anything. What the report states is how many cues measured the way this page measures them, which sentence each figure was read from, and what the page did not check.
- The figures here are the ones published at the time of writing, and each finding carries the day the sentence was last verified with a link to the page it came from. Published specifications change; the report tells you which version it measured against, and the document itself is the authority.
References
- Netflix English Timed Text Style Guide (USA) — reading speed: 20 characters per second for adult content, 17 for children's content. This is the source of the characters-per-second limit this page applies.
- Netflix Timed Text Style Guide: General Requirements — line length, maximum 42 characters per line, with 43 to 44 only in rare exceptions; duration, minimum five sixths of a second (20 frames at 24fps) and maximum seven seconds; and the maximum of two lines per subtitle event that this page reports as unchecked.