Why edits break subtitles
A subtitle file is a list of cues, each tied to a start and end time on the video’s timeline. The text does not know what is on screen; it only knows when to appear. If the picture changes and the timeline moves, the cues stay where they were and are suddenly wrong.
Re-edits are routine: a shorter version for social video, a new introduction, a corrected scene, a different ending or a version with an added logo sequence. In most cases much of the existing work can be reused, but it needs to be adjusted with care rather than copied across.
Identify what kind of change it is
The right fix depends on the type of edit. Most fall into a few groups.
Overall shift. Something has been added or removed at the very start, such as a new logo sequence. Every cue moves by the same amount. This is the simplest case: apply one offset to the whole file.
Insert or removal in the middle. Material has been added or cut partway through. Cues before the change stay put. Cues after it shift by the length of the change. Cues that overlap the edit point may need splitting, trimming or rewriting.
Reordered scenes. Sections have been moved. Each moved block has to be shifted separately, and any cues that depended on what came just before them, such as a sentence completed after a cut, need reading again.
Many small trims. The pace has been tightened throughout. Shifts differ from place to place, so a single offset will not work, and it is often easier to retime section by section.
Speed or frame-rate change. The whole video plays slightly faster or slower, or has been converted between frame rates. Timings must be scaled, not just shifted. The result of missing this is steady sync drift, which grows as the video plays. Frame rates matter here, so confirm both the old and the new rate.
Compare the old and new versions
Begin by comparing the two cuts side by side. Note each point where they diverge and write down the old timecode, the new timecode and what changed. This list of changes is the heart of the job. Even a rough list is far better than finding differences by chance while watching.
Several editing tools can export a change list from the video edit itself, and it is worth asking the editor for one. If none exists, watch both versions through once and mark the differences by hand.
Update the cues
With the change list in hand:
- Apply any global offset or scaling first.
- Work through the file from the first change to the last, shifting the cues after each edit point.
- Check each cue that touches an edit. A subtitle that runs across a cut may now cover a different scene and should be trimmed or split.
- Delete cues for removed material and write new ones for added material.
- Reread the text around each change to confirm sentences still make sense.
Cues near cuts deserve extra thought because syncing subtitles to shot changes is part of good timing. A cut that was not there before may now sit in the middle of a cue, and the cue may need to end on the cut or start after it.
Check gaps and durations
Shifting and trimming can leave cues too short, too long or crowded together. Look at the display duration of each affected cue and at cue gaps. A cue that was comfortable before may now leave too little reading time if the speech was tightened. Reading speed should be rechecked wherever the dialogue was shortened.
Translations follow the master
If the project has several languages, update the source-language file first, then pass each language the same list of changes. Translators then handle only new or altered text, and unchanged cues are retimed in the same way as the master. A translation memory can help with repeated or carried-over wording. Keep a note of which master version each language file matches, and follow sensible version control so you can tell old from new.
Watch the whole video again
Spot checks are not enough after a re-edit. Play the entire video with the subtitles, preferably in the final player. Look for cues that are early or late, text left over from removed scenes, and cues that now describe something that no longer happens. Fix what you find, then ask someone else to review the result.
When starting again is easier
If a re-edit is extensive, with most scenes moved, trimmed or replaced, reusing the cues may take longer than rebuilding the timing. A rough guide is to reuse the text but redo the spotting. The words and translations remain valuable even when the times do not.
Prevent repeat work
The best saving comes before subtitling starts: wait for a locked picture where possible, and tell the subtitler honestly when further changes are likely. Where changes are expected, ask the editor to keep the sequence of scenes stable and send a change list with each new cut.