It is a different problem from transcription, and easier. Transcription has to work out what was said; alignment already has the text and only has to place it on the timeline. Because the answer is constrained, alignment is accurate to a fraction of a second even where recognition would struggle.
This is the machinery behind captions that highlight word by word as they are spoken. Sentence-level subtitles need only rough timings; a caption that pops each word on the beat needs to know where every word starts and ends, and that is alignment output.
It also enables precise cutting. Knowing the timestamp of a specific word means you can trim a sentence exactly, remove a filler word without an audible seam, or split a long recording at natural boundaries rather than at arbitrary intervals.
In practice
- Feed it a corrected transcript — alignment inherits your typos as spoken words.
- Word-level timing is what animated caption styles consume.
- Music and overlapping speech degrade timing accuracy the same way they degrade transcription.
The mistake to avoid
Assuming captions are late because the alignment is wrong. More often the caption style has a display duration that outlives the word it belongs to.
Go deeper
Timed Captions From Speech: How Auto-Timing Works
How AI turns speech into perfectly timed captions: word-level timestamps, chunking logic, failure modes, and when to override auto-timing manually.
Where you will run into it
- Add Timed Text Overlays to a Video — Different words at different moments — you set the clock.
- Add Captions to a Video — Speech in, styled subtitles out — no manual timing.
- AI Caption Generator — Drop a video, get timed captions. Free, on your device, no upload.
Related terms
Speech-to-text
Speech-to-text meaning: converting spoken audio into written text, the transcript captions, translation, and search all depend on.
Lipsync
Lipsync meaning: driving a face mouth from an audio track so speech reads as spoken, not dubbed over the top.
AI dubbing
AI dubbing meaning: replacing spoken audio with another language, usually keeping the speaker voice and optionally re-syncing lips.
Voice Isolation
Voice isolation pulls speech away from traffic, room noise, and background music so only the voice remains, and it is not full stem separation.
Text-to-speech
Text-to-speech converts written text into spoken audio using a synthetic voice you choose before generating.
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