Subtitles drift progressively out of sync: how do you distinguish timebase and segment offsets?
For progressive subtitle drift, record offsets near the beginning, middle and end and distinguish fixed shifts, proportional drift and jumps after splices. Repeated global shifting does not repair an incorrect speed ratio.
Start troubleshooting here
For progressive subtitle drift, record offsets near the beginning, middle and end and distinguish fixed shifts, proportional drift and jumps after splices. Repeated global shifting does not repair an incorrect speed ratio. Check actual media duration, segment starts and subtitle timebase before choosing a correction that aligns the whole timeline rather than only the first sentence.
Measure sync near the beginning, middle and end
This applies when the start is correct but the end is far off or all cues shift after one segment. Preserve original subtitles and transcription audio and check whether silence was removed or speed changed afterward. Compare with the final video timeline, not another audio version of different duration. Identical filenames can still refer to different edits.
Separate fixed offset, accumulated drift and segment jumps
At clear words, record actual and subtitle times and inspect whether differences are constant or grow with duration. Check restoration of segment start offsets and retained gaps at concatenation. Subtitle formats use explicit time units; frames and seconds cannot be interchanged, and changing a frame-rate label may not transform time correctly.
Restore subtitle positions using the correct timebase
Apply a fixed shift only for constant offsets. For proportional drift, first correct media speed or time conversion; for segment jumps, inspect local starts. Afterward, validate cue start/end order, negative times and ordering. Do not repair only the first cue for an attractive preview. Preserve originals to compare and reverse incorrect transforms.
Replay the whole timeline and inspect cue boundaries
Replay different positions from start to end and inspect every splice, checking text against speech without abnormal overlap or lingering cues. Check pauses, the final sentence and the target player. Success means whole-timeline synchronization, not parseable subtitles. Automatic word timestamps still need verification against the actual media.
This article adjusted no private subtitles or measured a particular offset; it describes diagnosis. Time precision and frame-rate treatment vary by export tool. If original audio changed without edit records, realignment may be necessary. One linear transform cannot repair a complex timeline with independently varying segment speeds.
Checked sources
These sources support the concepts and methods described here. Examples and test scope are labeled separately; check the version of the tools you use.