Subtitle Quality Checklist: What to Check Before You Deliver
Most subtitle problems that reach a client or an audience could have been caught in ten minutes of checking. The challenge is knowing what to check, because a subtitle file can fail in four different ways: the words can be wrong, the timing can be wrong, the layout can be hard to read, or the file itself can be technically broken. This checklist walks through all four, in the order that saves the most time, and finishes with the most common file errors and what causes them.
How to use this checklist
Work through the sections in order. Fix technical problems first, because a broken file can make every later check misleading. Then proofread the text, then check timing and layout while playing the video. Doing text and timing in separate passes is faster and more reliable than trying to do both at once.
1. Technical checks on the file
- The file is saved as UTF-8 and special characters look correct when you open it in a plain text editor.
- The extension matches the real format: an SRT is named .srt, a WebVTT file is named .vtt.
- In SRT, entries are separated by a blank line, numbered in order, and use a comma before the milliseconds.
- In WebVTT, the file starts with the line WEBVTT and uses a period before the milliseconds.
- Every entry's start time is before its end time.
- The file opens and plays in at least two different players or editors.
If you are unsure whether a file is valid, run it through a converter: if our SRT to VTT or VTT to SRT tool reports that it cannot find valid subtitle entries, something is structurally wrong with the file.
2. Text checks
- Spelling and grammar are correct, including names, places and brand names. Spell each name the same way every time.
- Punctuation and capitalization follow one consistent style.
- Numbers, dates, units and currencies follow one convention across the whole file.
- Speaker changes are marked consistently, for example with a dash at the start of each speaker's line.
- Sound descriptions and music notes use one consistent format, and are present only if the audience needs them.
- Filler words and false starts are handled according to the style the client asked for, not at random.
A fast way to proofread the words is to take the timing out of the way. Use the SRT to TXT tool to get a clean transcript, paste it into a word processor or spell-checker, correct the text, and then make the same fixes in the subtitle file. Reading plain text also makes repeated words, missing words and inconsistent names much easier to spot than reading line by line in an editor.
3. Timing checks
- The first, middle and last subtitles are in sync with the audio.
- No subtitle appears before the words are spoken or stays long after they have ended.
- No two subtitles overlap in time, and consecutive subtitles have a short gap.
- No subtitle flashes by too quickly to read; reading speed stays within the agreed limit.
- No subtitle is on screen for far longer than it takes to read it.
- Subtitles do not straddle hard cuts when it can be avoided.
To check duration and reading speed across a whole file at once, convert it with the SRT to CSV tool and apply the spreadsheet formulas from our guide to subtitle reading speed. Sorting by characters per second brings the worst offenders straight to the top.
4. Layout checks
- No subtitle has more than two lines.
- Lines stay within the maximum length of your guideline, commonly about 42 characters.
- Line breaks fall at natural grammatical points, and the top line is no longer than the bottom line.
- Text does not cover important on-screen graphics, titles or faces more than necessary.
- Italics and other formatting are used consistently and render correctly in the target player.
5. Delivery checks
- The file format is exactly what was requested: SRT, WebVTT, or something else.
- The file name identifies the language, for example movie.en.srt and movie.es.srt, so players and platforms can match each file to the right language.
- If the subtitles are burned in, a clean version without them is archived.
- The final delivered file is the one you checked, not an earlier copy.
Common SRT errors and what causes them
| What you see | Likely cause | How to fix it |
|---|---|---|
| No subtitles appear at all | Wrong timestamp format (a period instead of a comma in SRT, or a single dash in the arrow), or the file has the wrong extension | Check one timestamp line against a known good file: 00:00:04,000 --> 00:00:06,500. |
| Two or more subtitles merge into one | A missing blank line between entries | Make sure each entry is followed by exactly one blank line. |
| Accents or special characters are wrong | The file is not saved as UTF-8 | Re-save the file as UTF-8 (see our guide to subtitle encoding problems). |
| Subtitles appear in the wrong order | Entries are not sorted by start time | Sort the entries by time and renumber them. |
| Text is cut off or runs off the screen | Too many characters on a line, or too many lines | Shorten the text or add line breaks at natural points. |
| The player skips some subtitles | A start time that is later than its end time, or overlapping entries | Correct the timestamps so each entry starts before it ends and does not overlap the next. |
A 10-minute pre-delivery routine
- 1Open the file in a text editor and confirm it is UTF-8 and well-formed.
- 2Extract the text with SRT to TXT and spell-check it.
- 3Export to CSV, calculate duration and characters per second, and fix the fastest lines.
- 4Watch the first minute, a section in the middle and the last minute with the subtitles on.
- 5Check line lengths and breaks on the longest subtitles.
- 6Save with the correct file name, and test in a second player.
Frequently asked questions
- How long should a subtitle quality check take?
- For a short video, the routine in this guide takes about ten minutes. Longer content takes proportionally longer, but doing the technical and text checks first prevents most of the rework later.
- Is it enough to run an automatic spell-check?
- A spell-check catches typos but not wrong words that are spelled correctly, misspelled names that the dictionary does not know, or mistakes in timing and layout. Use it as one step, not the whole check.
- Should the file name include the language?
- Yes, it helps. A name such as movie.en.srt makes the language clear to people and often lets players and platforms detect it automatically when the subtitle sits next to the video file.
- What is the quickest way to test that a subtitle file is valid?
- Play it in two different players. A file that works in both is very likely valid, and one that fails in either deserves a closer look at its timestamps and structure.