What is forced alignment? Matching supplied text to audio timing
Understand alignment versus recognition through corrected subtitles, including language, dictionaries, missing words, boundaries, offsets, and caption pacing.
Understand the concept
Forced alignment matches supplied transcripts to audio to estimate word or phoneme timing. Unlike recognition, it usually assumes text broadly matches speech. Errors and omissions can distort alignment. Fine timestamps do not verify wording, and captions still need segmentation and listening checks.
Correct text before locating it in audio
If a transcript omits “turn off” from an instruction, remaining words may align poorly. Correct text by listening first. Start-end times do not prove the recording contained a supplied sentence.
MFA pairs audio and transcripts with matching acoustic models and dictionaries. Other methods differ; WhisperX combines VAD and phoneme alignment. MFA-specific input rules are not universal alignment requirements.
Language and segment offsets affect timing
Uncovered names and pronunciation mismatches can harm boundaries. Chinese segmentation and number readings change units. Chunk-relative times need correct global offsets when merging long recordings.
Noise and overlap can shift boundaries. Listen at key words instead of trusting decimal precision. No audio or aligner was run, and paper speedups are not claimed for this environment.
Word timing still needs readable caption segmentation
Word timing helps navigation, but captions need semantic and visual grouping rather than one word per screen. Check long sentences, pauses, and speaker changes. Separate text correction from display formatting.
Test known passages near starts, ends, and pauses and replay final video. This is validation design without scores. Preserve audio and input text for correction; valid time syntax does not establish correct alignment.
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.