How to Run a Quality Check on a Finished Subtitle File

What a subtitle QC pass is, and what to gather first

QC is not translation and not transcript proofreading. By the time a file reaches QC, someone has already produced and edited it. The QC pass checks the finished deliverable as a viewer will experience it, with the picture, at normal speed, in the actual file format. Correcting the underlying transcript word by word is a separate job, covered in how to proofread an AI transcript, and checking a dubbed voice track has its own AI dubbing quality checklist.

Before starting, collect:

• The exact video version the subtitles are for, with its duration and frame rate.
• The subtitle file and its version number or date.
• The style guide or delivery spec, if one exists: line length, cue duration limits, italics policy, number format.
• A glossary of names, products and technical terms in each language.
• For translated files, a fluent reviewer, or at least the source-language file for reference.

A checker who did not produce the file catches more. Fresh eyes notice what the author reads past.

Text accuracy

Watch with sound and read every cue. For each, ask whether it says what was said, or for a translation, whether it means what was meant.

• Names of people, places, companies and products spelled correctly and consistently.
• Numbers, dates, prices and units right, and converted where the style guide says so.
• Negations intact. A dropped "not" reverses the meaning and is easy to miss.
• No missing speech. Look for gaps where someone talks and no cue appears.
• No invented text, such as a phrase repeated in a silent passage or a stock sign-off that nobody said.
• Spelling, grammar and punctuation in the subtitle language.
• Translations that keep tone and register: a casual remark should not become stiff, and a formal statement should not become slang.

Timing and reading speed

Timing problems are the ones viewers notice first. Check that each cue appears close to when its speech starts and disappears soon after it ends, with no cue staying up over a shot of someone else speaking. Watch the opening, a section in the middle and the last few minutes in particular, because a file that starts in sync can drift.

Reading speed matters as much as sync: a cue can be perfectly timed and still flash past too quickly to read. Many subtitle tools display characters per second for each cue, so sort by that column and look at the fastest ones first. How recognized timestamps become cues, what reading-speed limits style guides commonly use, and how to repair drift are covered in subtitle timestamp alignment; QC only needs to find the cues that break your chosen limits.

Segmentation and line breaks

Check how text is divided into cues and lines. A good cue holds a unit of sense; a poor one splits a name, separates an article from its noun or ends mid-phrase so the viewer must hold a fragment in memory. Look for:

• Lines longer than your style guide or platform allows.
• Cues that break inside a phrase when a nearby pause would be better.
• Very short cues that blink on and off, and very long ones that cover several sentences.
• Two-line cues with awkward shapes, where one line is a single word.

The principles behind good divisions are explained in subtitle segmentation. In QC, flag the worst offenders and decide whether they block release.

Consistency

Consistency issues rarely change meaning, but they make a file feel careless, and across a series they confuse viewers.

• The same term translated the same way throughout, matching the glossary.
• Names and titles in one form: not "Dr Patel" in one cue and "Doctor Patel" in the next unless the speaker changes.
• One number style, one date style, one quotation-mark style.
• Italics, dashes and capitalization used to one convention, if the style guide allows them at all.
• Formality consistent, for languages with formal and informal address.

Technical validity

A file that fails to load is a critical failure no matter how good the text is. Check the file itself, ideally in a subtitle editor that reports errors:

• Cues numbered in order with no gaps or duplicates (for SRT).
• Every timestamp well formed, with end times after start times.
• No overlapping cues, unless the format and platform allow them deliberately.
• No cue extending past the end of the video.
• The right encoding, normally UTF-8, with accented and non-Latin characters displaying correctly.
• The correct file extension and a file name that follows the platform's or client's convention.

If the file refuses to load anywhere, the causes and fixes are in SRT file not working.

Playback on the target platform

Desktop subtitle editors render text their own way. The real test is the player your audience uses. Upload or attach the file where it will be published, privately if possible, and watch a few minutes at the start, middle and end. Check that:

• The file is accepted and assigned the right language.
• Text is readable at the platform's size and does not collide with its interface controls.
• Long lines wrap acceptably, or are not wrapped at all if the platform refuses them.
• Characters display correctly, especially for right-to-left and non-Latin scripts.
• Timing still matches after the platform's processing.

Repeat on a phone if a large share of your audience watches on phones. Attaching files to common platforms is covered in how to add subtitles to a video.

Severity levels and the sign-off record

Not every issue needs to block release. Grading each one keeps QC proportionate and gives everyone the same language for decisions.

Critical

Changes or reverses meaning, offensive or legally risky error, missing or wrong-language section, file fails to load. Blocks release

Major

Wrong name or number, cue noticeably out of sync, cue too fast to read, line that breaks the platform. Fix before release unless explicitly accepted

Minor

Punctuation, small style inconsistency, slightly awkward line break. Fix if time allows

Preference

Reviewer would phrase it differently but the cue is correct. Note only

Close the pass with a short record kept beside the file: file name and version, language, video version and duration, checker's name, date, count of issues by severity, what was fixed, what was accepted and why, and a decision (pass, pass with notes, or fail). When the file changes later, the record shows which version was approved.

Common QC mistakes and limits

• Checking the text in a document without the video, which hides every timing and segmentation problem.
• Checking at double speed to save time. Reading speed problems only show at normal speed.
• Testing in a desktop player only and finding on release that the platform rejects the file.
• Letting the person who made the file sign it off alone.
• Treating every issue as equal, so either nothing ships or nothing gets fixed.
• Expecting QC to rescue a poor file. If critical issues keep appearing, stop and send the file back for proper editing rather than patching cue by cue.

QC also cannot verify a translation into a language nobody on the team reads. In that case, the honest record says the language was checked technically and for timing only, and a fluent reviewer is still needed.

Running QC on mydubly subtitle files

mydubly's SRT and VTT files are UTF-8 with a byte order mark, numbered in order, with one single-line cue per recognized speech segment, in the spoken language or the target language. A few checks deserve extra attention with them:

• Cue boundaries follow recognized speech segments, not sense units, so look for cues that break mid-phrase and for long single lines that need splitting for your platform.
• The files contain recognized speech only, with no italics, sound tags, speaker labels or positioning; if your spec requires any of these, they must be added by hand, and captions for accessibility use should be reviewed by a person.
• For a dubbed job, the target-language subtitles follow the dubbed lines, so check them against the dubbed video rather than the original.
• mydubly cannot re-import an edited file, so make corrections in a subtitle editor and keep the edited file as the master.

The subtitle generator page shows the file structure, and AI video translation explains what a translated job returns.

Next step: write your QC record template once

Turn the seven checks and the severity table into a one-page template your team reuses for every file and language. The first time takes an hour; after that, every QC pass ends with a record that shows exactly what was approved.