Turn an SRT File into a Voiceover That Stays in Sync

An SRT file is a list of numbered blocks, each with a start time, an end time and a line of text. That makes it a perfect blueprint for a voiceover: you already know exactly when each sentence should be heard. The difficulty is that spoken language does not care about your timestamps. A line that takes two seconds to read on screen may take four seconds to say aloud, and a voiceover that runs long on every line drifts further out of sync as the video goes on.

How speed fitting works

SRT to Audio generates each subtitle separately and measures how long it runs. If the audio is longer than its time slot, the speaking rate is increased until it fits; if it is much shorter, it can be slowed slightly. You set the minimum and maximum rate, so a line is never squeezed beyond what you consider natural. When even the maximum rate cannot make a line fit, that is a sign to edit the text — not to push the speed higher.

Prepare the subtitles before you generate

Subtitles written for reading are often too dense for listening. A few minutes of cleanup saves a lot of regeneration later.

• Merge fragments. Two blocks that split one sentence in half produce an odd pause in the middle. Join them.
• Cut filler. Reading subtitles tolerate repetition; a voice reading them does not. Trim “you know”, “so, basically” and repeated words.
• Spell out what should be spoken: numbers, abbreviations, units and symbols. “3 km” and “three kilometres” sound different.
• Remove sound descriptions like [music] or (laughs) unless you use them as speaker or emotion tags on purpose.

One voice or several

For a single narrator, pick one voice and you are done. For interviews, dialogues or explainers with two presenters, prefix lines with speaker tags such as [A] and [B]. Each tag can then be given its own voice — a stock voice, your cloned voice, or a designed one — and the whole file is voiced in one pass.

Translating while you voice

If the subtitles are in one language and the voiceover should be in another, turn on translation before generating. The tool translates each block, keeps the original timing and then voices the translation. Translated lines are often longer than the source — Vietnamese and Spanish typically run longer than English — so review the overflow lines and shorten them in the translated SRT. A glossary keeps product names and recurring terms consistent across the whole file.

Check, export, and re-use

1. Generate a short section first and play it against the video.
2. Fix any line that sounds rushed by editing the text, not by raising the maximum speed.
3. Generate the full file and download the MP3.
4. Download the edited or translated SRT as well — it now matches the audio exactly and doubles as on-screen subtitles.

Limits to keep in mind: the tool accepts .srt files up to 2 MB, and each run is billed by characters at the rate of the voice you choose. VocaTTS does not transcribe video, so you need an SRT to start with — most editing tools and video platforms can export one.