Subtitle QC checklist: what to check before you deliver

Updated 17 October 2026. Written by the team behind Subtidy.

In short: subtitle QC is a rule check, a watch-through and a test in the place the file is going. The rule check covers line length, lines per subtitle, reading speed, duration, gaps and overlaps. Software can find all of these from the file alone and fix most of them. The watch-through covers what needs the picture and the sound: sync to speech, shot changes, line breaks, spelling and meaning. Then test the file where it will play, and run the rule check again after every edit.

Run the rule check on your file See it on a sample

Which subtitle QC checks can be automated?

Anything that can be measured from the text and the timestamps. Anything that needs the picture, the sound or an understanding of the words still needs a person.

Check	Can software find it?	Does Subtidy fix it?	What still needs a person
Characters per line	Yes, from the file	Yes, rewraps the lines	Moving a break that splits a phrase
Lines per subtitle	Yes, from the file	Yes, splits the cue	Checking where the split falls
Reading speed	Yes, from the file	Partly, adds time from free space	Shortening text when there is no time left
Minimum and maximum duration	Yes, from the file	Yes	Cues with no free time around them
Overlaps and minimum gap	Yes, from the file	Yes	Nothing
Short gaps that should be closed	Yes, from the file	No	Closing them in your editor
Cue order, numbering, empty cues	Yes, from the file	Yes	Nothing
Text encoding	Partly	Reads UTF-8, UTF-16 and Windows-1252, saves UTF-8	Checking accents and right-to-left text in the target app
Drift after a frame rate change	Yes, against the video	Pro, converts the frame rate	Measuring the drift first
Sync to speech	Only with the audio	No	Watching with sound
Shot changes	Only with the video	No	Watching the picture
Covering on-screen text	Only with the video	No	Watching the picture
Line breaks by meaning	No	No	Reading each subtitle
Spelling, names and terms	Partly, with a spell checker	No	Proofreading
Translation and meaning	No	No	A translator or reviewer

So the order matters. Let software do the arithmetic first, then spend the watch-through on judgement.

Step 1: get the spec

Every check depends on the limits the client or platform sets. Before you start, ask for:

Characters per line and lines per subtitle.
Maximum reading speed, in characters per second or words per minute, and how characters are counted.
Minimum and maximum time on screen.
The minimum gap between subtitles, and whether short gaps must be closed.
Rules for shot changes.
File format, encoding and frame rate.
House style: italics, dashes for speaker changes, numbers, sound labels for SDH.

If there is no written spec, ask which platform the subtitles are for and use that platform's published guide. Two of the most detailed are Netflix's and the BBC's:

Rule	Netflix, English	BBC
Characters per line	42	37 on broadcast (Teletext); online, 68% of the width of 16:9 video
Lines per subtitle	2	2 for 16:9, up to 3 for 9:16
Reading speed	20 CPS adult, 17 CPS children's	160 to 180 words per minute
Time on screen	5/6 of a second to 7 seconds	About 0.3 seconds per word as a minimum
Gaps	At least 2 frames; gaps under half a second closed to 2 frames	A gap left in a pause should be at least 1 second, preferably 1.5
Sync	In time on the first frame of speech, or within 1 or 2 frames	Subtitles appear when speech starts

Netflix publishes separate guides for each language, with their own limits. Subtidy is not affiliated with Netflix or the BBC.

Step 2: run the rule check and fix what software can

Open the subtitle file in a checker that uses your limits. In Subtidy, pick Streaming, Broadcast or Social vertical, or set custom limits with Pro.
Apply the automatic fixes: line rebalancing, splitting overfull cues, closing overlaps, keeping the minimum gap, and extending fast or short cues into free time. Subtidy does all of these in one pass and never rewrites your words.
Read the before and after counts. Every cue that still fails a rule is one you have to edit by hand, usually because the text is too long for the time available.
Note the cues whose timing moved. Subtidy can start a cue up to 300 ms early to make room for reading, which a strict spec may not accept, so check those during the watch-through.

More on what gets fixed, with a worked example: SRT fixer.

Step 3: watch it with picture and sound

Each subtitle appears when the speech starts. Netflix asks for the first frame of speech, or within one or two frames of it. The BBC says subtitles should appear at speech onset.
Each subtitle stays until the line is finished, and does not hang on into an unrelated shot.
Shot changes are respected. Both Netflix and the BBC have detailed rules for subtitles that start, end or cross near a shot change.
Short gaps are closed if the spec asks for it. Netflix closes gaps under half a second to two frames.
Text that still reads too fast is condensed, keeping the meaning and the speaker's voice.
Line breaks fall at natural points, never between an article and its noun or a first name and a last name. See line breaks.
Subtitles do not cover on-screen text or the speaker's mouth. Move them if they do.
Spelling, names and terms are right and consistent across episodes. Netflix recommends keeping a table of key names and phrases.
Speaker changes and sound labels follow the house style.

Step 4: test it where it is going

Format and file name match the spec. For Netflix, check the current delivery specification.
It imports. Open it in Premiere Pro, DaVinci Resolve, YouTube or the client's platform and check that every subtitle appears.
Characters display correctly, including accents and right-to-left text such as Urdu and Arabic.
Timing matches the final cut. Check one line near the start and one near the end. If the error grows through the programme, it is a frame rate problem; see subtitles drifting out of sync.
Burned-in subtitles stay in the safe area: inside title safe for 16:9, and clear of the app buttons for vertical video.

Step 5: check again after every edit

Every manual fix can break another rule. Shortening a line changes its reading speed, and moving an in time to a shot change can create an overlap. Run the rule check on the final file before you export it. It should report no problems, or only ones you have chosen to accept and can explain to the client.

The checklist, to copy

Plain text, for a delivery note or a job sheet.

Subtitle QC before delivery
[ ] Spec: characters per line, lines, reading speed, min and max duration, gap, shot change rules, format, encoding, frame rate
[ ] Rule check run with the spec's limits
[ ] Automatic fixes applied: line breaks, splits, overlaps, gaps, reading time
[ ] Cues still failing a rule edited by hand
[ ] Watched with sound: subtitles appear with the speech
[ ] Shot changes respected
[ ] Short gaps closed, if the spec asks
[ ] Line breaks at natural points
[ ] Nothing covers on-screen text or the speaker's mouth
[ ] Spelling, names and terms checked and consistent
[ ] Speaker changes and sound labels in house style
[ ] Imported into the target app, every subtitle shows
[ ] Accents and right-to-left text display correctly
[ ] Timing matches the final cut at the start and the end
[ ] Burned-in subtitles inside the safe area
[ ] Rule check run again on the final file

Run the rule check on your file

Subtidy checks and fixes SRT, WebVTT and ASS files in your browser and shows the problems before and after. Free for one file at a time, with SRT export. Nothing is uploaded.

Open with Streaming Broadcast Social vertical

Sources

Netflix Partner Help Center, English (USA) Timed Text Style Guide, updated 19 December 2025.
Netflix Partner Help Center, Timed Text Style Guide: General Requirements.
Netflix Partner Help Center, Timed Text Style Guide: Subtitle Timing Guidelines, updated 4 July 2025.
BBC, Subtitle Guidelines, version 1.2.5, March 2026: sections 3 Line breaks, 4 Timing, 5 Synchronisation, 6 Matching shots and 10.1 Vertical positioning.