Three families of error
Subtitle problems fall into three broad families: what the text says, when it appears, and how it looks on screen. Sorting errors this way is useful because each family is found with a different kind of check. Text errors show up when you read. Timing errors show up when you watch with sound. Layout errors show up when you look at the picture and the text together.
Text errors
Misheard or wrong words. The most obvious error is a word that differs from what was said. Sound-alike swaps are typical, especially in automatic output, where a rare word is replaced with a common one that sounds similar. Spot them by reading each line for sense: if a sentence is grammatical but odd, play the audio.
Omissions. Words or whole sentences are missing. Some omission is deliberate, since subtitles usually condense speech, but dropping a negative (“not”), a number or a key fact changes the meaning. Watch particularly for lost negatives.
Additions and invented text. Occasionally extra words appear that nobody said. Automated tools sometimes produce text during silence or music, which is easy to miss unless you compare against the audio.
Meaning errors in translation. A literal translation of an idiom, a false friend between two languages or a misread joke can produce subtitles that are fluent but wrong. Only a reviewer who knows both languages will reliably catch these.
Names and specialist terms. Inconsistent or incorrect spelling of names and terms is among the most frequent faults. Searching the file for each key name is the quickest check.
Spelling, grammar and punctuation. Typos, missing apostrophes, wrong homophones and inconsistent capitalization. A spell-check helps, but it will not flag a correctly spelled wrong word.
Inconsistency. The same thing written differently in different places: “OK” and “okay,” numerals and spelled-out numbers, varying hyphenation. These are signs that no style guide or glossary was followed.
Number and symbol mistakes. Wrong digits, misplaced decimal points and inconsistent handling of dates, times and units. Because numbers carry specific information, check them against the audio every time. Rules for number formatting vary between style guides, so consistency within the file matters.
Speaker confusion. Dialogue that appears to come from the wrong person, or missing speaker identification when two people talk in quick succession.
Timing errors
Late or early cues. Text that arrives noticeably after the words, or before them. A short offset is tolerated more easily than a long one, but a viewer who relies on the text will feel it.
Progressive drift. The subtitles start in sync but slide further out as the video plays. This is often the sign of a frame-rate mismatch or an edit made to the video after the subtitles were timed. Checking the start, middle and end of a file is a quick test, and sync drift is explained in more detail elsewhere.
Too short on screen. A cue that disappears before it can be read. Count how much text there is and compare it with the time shown: a long line on screen for a split second is a warning sign. Poor display duration and high reading speed usually go together.
Too long on screen. Text that lingers well after the speaker has stopped, or carries over into the next scene.
Missing gaps. When cue gaps are too small or absent, successive subtitles blur together and the viewer cannot tell that the text has changed. Overlapping cues are a related fault.
Crossing shot changes. A subtitle that starts just before a cut, or ends just after one, can cause visual flicker. It is a polish issue more than a fault in meaning.
Layout and presentation errors
Too many lines or too long lines. Text that fills much of the screen or runs past the limits in the style guide. Most guides keep to two lines, and a three-line cue usually signals that it needs to be condensed or split.
Awkward line breaks. A break between an article and its noun, or in the middle of a name, forces the viewer to re-read. Read the cue aloud: if you stumble at the break, so will the viewer.
Covering important picture content. Subtitles that sit over on-screen text, a speaker’s mouth or an important graphic.
Poor contrast or tiny text. Light text over a bright background, or a size that is hard to read on a phone. Subtitle legibility is easy to test by viewing on a small screen.
Inconsistent styling. Colors, italics or positions that change without a reason. Italics for off-screen voices or foreign words are common conventions, but only if applied consistently.
Missing non-speech information. For captions meant for viewers who are deaf or hard of hearing, relevant sounds or music may be absent. Whether this is expected depends on what type of subtitles the project promised.
Technical errors
Some faults sit in the file rather than in the viewing experience. Garbled accented characters point to a character encoding problem. A file that will not load, or that shows nothing, may be in the wrong format for the player, a question covered under file formats. A subtitle track labeled with the wrong language is also surprisingly common.
How to find them efficiently
A single pass will not catch everything, because the eye cannot track text, timing and layout at once. Reviewers commonly make several passes: one reading the text alone, one watching with sound for timing, and one checking visual presentation. Playing the file in the same player or on the same devices that audiences will use finds problems that never show in an editing tool.
Not every flaw is equally serious. A wrong number in a safety instruction matters far more than a slightly awkward line break. When there are many issues, fix meaning errors first, then timing, then polish.
Finally, remember that listing errors is a tool for noticing, not a score. A file with few errors can still be hard to follow, and a file with some minor ones may serve its audience well. Judging overall quality means weighing what the errors do to the viewer’s understanding.