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.
Related terms
Speech-to-text
Speech-to-text converts spoken audio into written text, producing the transcript that captions, translation and search all depend on.
Lipsync
Lipsync generation drives a face's mouth from an audio track, so the speech reads as spoken rather than dubbed over the top.
AI dubbing
AI dubbing replaces a video's spoken audio with another language, usually keeping the original speaker's voice and optionally re-syncing their mouth.
Voice isolation
Voice isolation separates speech from everything else in a recording — traffic, room noise, music — and keeps only the voice.
Text-to-speech
Text-to-speech converts written text into spoken audio using a synthetic voice you choose before generating.
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