Subtitle Quality Checklist: Timing, Length and Readability

Subtitle QA should produce evidence, not a vague “looks good.” Combine automated checks with playback review. Automation finds malformed timestamps and excessive line length; a human determines whether a punchline appears early, a name is wrong, or captions cover essential graphics.

File integrity

• File opens as the declared format and encoding.
• Cue identifiers are unique where required.
• Every start precedes its end.
• Cues are ordered and no timestamp is negative.
• Blank separators, headers, and millisecond punctuation are valid.
• No replacement characters (�) or suspicious mojibake remain.

Use the UTF-8 repair guide if text is corrupted and SRT vs VTT if the delivery format is uncertain.

Text accuracy

Verify names, numbers, commands, URLs, and terminology against authoritative references. Search for double spaces, repeated punctuation, empty cues, untranslated source fragments, and inconsistent capitalization. Confirm that cleanup did not delete intentional repetition.

Timing

Check cue lead-in and tail against speech, gaps between cues, overlaps, shot changes, and synchronization at the beginning, middle, and end. Equal error suggests offset; growing error suggests drift. Follow the timing guide rather than nudging random cues.

Example failure:

20
00:01:10,000 --> 00:01:10,800
This complete sentence cannot be read in eight-tenths of a second.

Valid syntax is not acceptable timing. Extend, compress text, or resegment based on audio and neighboring cues.

Length and readability

Apply the client’s line-length, line-count, duration, and reading-speed limits. Treat automatic flags as review items. A URL or product token may justify an exception; a routine sentence usually does not.

Break at syntax boundaries. Avoid separating names, articles and nouns, prepositions and objects, or numbers and units. Review splitting long subtitles for practical examples.

Visual placement

Test captions on the actual player and on mobile. Confirm they do not cover lower-thirds, burned-in text, faces, or essential UI. If WebVTT positioning is used, verify fallback behavior. Do not assume editor preview matches every delivery player.

Accessibility content

For captions, confirm meaningful sound effects, music, and unclear speakers are identified consistently. Do not add unsupported speaker names. For translation subtitles, avoid overloading lines with unnecessary sound descriptions unless required.

Translation QA

Review meaning in context, terminology consistency, grammar, reading speed, and cue segmentation. Ensure timestamps and placeholders survived the workflow. Translate SRT without breaking timestamps describes structural checks.

Delivery package

Include final file, language and locale, format, frame rate if relevant, source video version, style guide, change notes, and known exceptions. Retain the source and validation report.

Playback sampling plan

Watch the opening two minutes, every known problem area, rapid dialogue, speaker changes, graphics-heavy sections, a middle sample, and the ending. For short videos, watch the entire program. Mute once to test whether the text stands alone, then listen to verify alignment and transcription.

This checklist is the QA gate in the complete YouTube subtitle workflow, after timing and translation and before TTS, dubbing, or publication.